Engaging Image Captioning Via Personality

by   Kurt Shuster, et al.

Standard image captioning tasks such as COCO and Flickr30k are factual, neutral in tone and (to a human) state the obvious (e.g., "a man playing a guitar"). While such tasks are useful to verify that a machine understands the content of an image, they are not engaging to humans as captions. With this in mind we define a new task, Personality-Captions, where the goal is to be as engaging to humans as possible by incorporating controllable style and personality traits. We collect and release a large dataset of 201,858 of such captions conditioned over 215 possible traits. We build models that combine existing work from (i) sentence representations (Mazare et al., 2018) with Transformers trained on 1.7 billion dialogue examples; and (ii) image representations (Mahajan et al., 2018) with ResNets trained on 3.5 billion social media images. We obtain state-of-the-art performance on Flickr30k and COCO, and strong performance on our new task. Finally, online evaluations validate that our task and models are engaging to humans, with our best model close to human performance.


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1 Introduction

If we want machines to communicate with humans, they must be able to capture our interest, which means spanning both the ability to understand and the ability to be engaging, in particular to display emotion and personality as well as conversational function (Jay & Janschewitz, 2007; Jonczyk & Jończyk, 2016; Scheutz et al., 2006; Kampman et al., 2019).

Communication grounded in images is naturally engaging to humans (Hu et al., 2014)

, and yet the majority of studies in the machine learning community have so far focused on function only: standard image captioning

(Pan et al., 2004) requires the machine to generate a sentence which factually describes the elements of the scene in a neutral tone. Similarly, visual question answering (Antol et al., 2015) and visual dialogue (Das et al., 2017) require the machine to answer factual questions about the contents of the image, either in single turn or dialogue form. They assess whether the machine can perform basic perception over the image which humans take for granted. Hence, they are useful for developing models that understand content, but are not useful as an end application unless the human cannot see the image, e.g. due to visual impairment (Gurari et al., 2018).

Standard image captioning tasks simply state the obvious, and are not considered engaging captions by humans. For example, in the COCO (Chen et al., 2015) and Flickr30k (Young et al., 2014) tasks, some examples of captions include “a large bus sitting next to a very tall building” and “a butcher cutting an animal to sell”, which describe the contents of those images in a personality-free, factual manner. However, humans consider engaging and effective captions ones that “avoid stating the obvious”, as shown by advice to human captioners outside of machine learning.111https://www.photoup.net/how-to-write-more-engaging-photo-captions/ For example, “If the bride and groom are smiling at each other, don’t write that they are smiling at each other. The photo already visually shows what the subject is doing. Rephrase the caption to reflect the story behind the image”. Moreover, it is considered that “conversational language works best. Write the caption as though you are talking to a family member or friend”.222https://www.poynter.org/news/6-tips-writing-photo-captions These instructions for human captioners to engage human readers seem to be in direct opposition to standard captioning datasets.

In this work we focus on image captioning that is engaging for humans by incorporating personality. As no large dataset exists that covers the range of human personalities, we build and release a new dataset, Personality-Captions, with 201,858 captions, each conditioned on one of 215 different possible personality traits. We show that such captions are far more engaging to humans than traditional ones.

We then develop model architectures that can simultaneously understand image content and provide engaging captions for humans. To build strong models, we consider both retrieval and generative variants, and leverage state-of-the-art modules from both the vision and language domains. For image representations, we employ the work of Mahajan et al. (2018) that uses a ResNeXt architecture trained on 3.5 billion social media images which we apply to both. For text, we use a Transformer sentence representation following (Mazaré et al., 2018) trained on 1.7 billion dialogue examples. Our generative model gives a new state-of-the-art on caption generation on COCO, and our retrieval architecture, TransResNet, yields the highest known hits@1 score on the Flickr30k dataset. To make the models more engaging to humans, we then adapt those same architectures to the Personality-Captions task by conditioning the input image on the given personality traits, giving strong performance on our new task. In particular, when compared to human captions, annotators preferred our retrieval model’s captions over human ones 49.5% of the time, where the difference is not statistically significant.

Standard captioning output: A plate with a sandwich and salad on it.
Our model with different personality traits:
Sweet That is a lovely sandwich.
Dramatic This sandwich looks so delicious! My goodness!
Anxious I’m afraid this might make me sick if I eat it.
Sympathetic I feel so bad for that carrot, about to be consumed.
Arrogant I make better food than this
Optimistic It will taste positively wonderful!
Money-minded I would totally pay $100 for this plate.
Figure 1: Comparison of a standard captioning model compared to our TransResNet model’s predictions on the same image conditioned on various personality traits. Our model is trained on the new Personality-Captions dataset which covers 215 different personality traits. The standard captioning system used for comparison is the best COCO UpDown model described in Section 4.2.

2 Related Work

A large body of work has focused on developing image captioning datasets and models that work on them. In this paper we also perform experiments on the COCO (Chen et al., 2015) and Flickr30k (Young et al., 2014) datasets, comparing to a range of models, including both generative models such as in (Vinyals et al., 2015; Xu et al., 2015; Anderson et al., 2018) and retrieval based such as in (Gu et al., 2017; Faghri et al., 2017; Nam et al., 2016). These setups measure the ability of models to understand the content of an image, but do not address more natural human communication.

A number of works have tried to induce more engaging captions for human readers. One area of study is to make the caption personalized to the reader, e.g. by using user level features such as location and age (Denton et al., 2015) or knowledge of the reader’s active vocabulary (Park et al., 2017). Our work does not address this issue. Another research direction is to attempt to produce amusing captions either through wordplay (puns) (Chandrasekaran et al., 2017) or training on data from humour websites (Yoshida et al., 2018). Our work focuses on a general set of personality traits, not on humour. Finally, closer to our work are approaches that attempt to model the style of the caption. Some methods have tried to learn style in an unsupervised fashion, as a supervised dataset like we have built in this work was not available. As a result, evaluation was more challenging in those works, see e.g. Mathews et al. (2018). Others such as You et al. (2018) have used small datasets like SentiCap (Mathews et al., 2016) with 800 images to inject sentiment into captions. Gan et al. (2017) collect a somewhat bigger dataset with 10,000 examples, FlickrStyle10K, but only covers two types of style (romantic and humorous). In contrast, our models are trained on the Personality-Captions dataset that has 215 traits and 200,000 images.

Split train valid test
Number of Examples 186,858 5,000 10,000
Number of Personality Types 215 215 215
Vocabulary Size 35559 5557 8137
Average Tokens per Caption 11.6 11.2 11.4
Table 1: Personality-Captions dataset statistics.

Our work can also be linked to the more general area of human communication, separate from just factual captioning, in particular image grounded conversations between humans (Mostafazadeh et al., 2017) or dialogue in general where displaying personality is important (Zhang et al., 2018). In those tasks, simple word overlap based automatic metrics are shown to perform weakly (Liu et al., 2016) due to the intrinsically more diverse outputs in the tasks. As in those domains, we thus also perform human evaluations in this work to measure the engagingness of our setup and models.

In terms of modeling, image captioning performance is clearly boosted with any advancements in image or text encoders, particularly the former. In this work we make use of the latest advancements in image encoding by using the work of Mahajan et al. (2018)

which provides state-of-the-art performance on Imagenet image classification, but has so far not been applied to captioning. For text encoding we use the latest advances in attention-based representations using Transformers

(Vaswani et al., 2017); in particular, their use in retrieval models for dialogue by large-scale pretraining (Mazaré et al., 2018) is adapted here for our captioning tasks.

3 Personality-Captions

The Personality-Captions dataset is a large collection of (image, personality trait, caption) triples that we collected using crowd-workers, made available in ParlAI (http://parl.ai).

We considered 215 possible personality traits which were constructed by selecting a subset from a curated list of 638 traits333http://ideonomy.mit.edu/essays/traits.html that we deemed suitable for our captioning task. The traits are categorized into three classes: positive (e.g., sweet, happy, eloquent, humble, perceptive, witty), neutral (e.g., old-fashioned, skeptical, solemn, questioning) and negative (e.g., anxious, childish, critical, fickle, frivolous). Examples of traits that we did not use are allocentric, insouciant, flexible, earthy and invisible, due to the difficulty of their interpretation with respect to captioning an image.

We use a randomly selected set of the images from the YFFC100M Dataset444https://multimediacommons.wordpress.com/yfcc100m-core-dataset/; Thomee et al. (2016) to build our training, validation and test sets, selecting for each chosen image a random personality trait from our list.

In each annotation round, an annotator is shown an image along with a trait. The annotators are then asked to write an engaging caption for the image in the context of the personality trait. It was emphasized that the personality trait describes a trait of the author of the caption, not properties of the content of the image. See Section D in the appendix for the exact instructions given to annotators.

4 Models

We consider two classes of models for caption prediction: retrieval models and generative models. Retrieval models produce a caption by considering any caption in the training set as a possible candidate response. Generative models generate word-by-word novel sentences conditioned on the image and personality trait (using a beam). Both approaches require an image encoder.

4.1 Image Encoders

We build both types of model on top of pretrained image features, and compare the performance of two types of image encoders. The first is a residual network with 152 layers described in (He et al., 2015) trained on Imagenet (Russakovsky et al., 2014)

to classify images among 1000 classes, which we refer to in the rest of the paper as

ResNet152 features. We used the implementation provided in the torchvision project (Marcel & Rodriguez, 2010). The second is a ResNeXt d (Xie et al., 2016) trained on 3.5 billion Instagram pictures following the procedure described by Mahajan et al. (2018), which we refer to in the rest of the paper as ResNeXt-IG-3.5B

. The authors provided the weights of their trained model to us. Both networks embed images in a 2048-dimensional vector which is the input for most of our models. In some of the caption generation models that make use of attention, we keep the spatial extent of the features by adapting activation before the last average pooling layer, and thus extract features with


4.2 Caption generation models

We re-implemented three widely used previous/current state-of-the-art methods (Vinyals et al., 2015; Xu et al., 2015; Anderson et al., 2018) for image captioning as representatives of caption generation models. We refer them as ShowTell, ShowAttTell and UpDown respectively.

Image and Personality Encoders

We extract the image representation using the aforementioned image encoders. The ShowTell model uses image features with 2048 dimensions and the other models use image features with dimensions. In the case where we augment our models with personality traits, we learn an embedding for each trait, which is concatenated with each input of the decoder.

Caption Decoders

The ShowTell model first applies a linear projection to reduce image features into a feature vector with 512 dimensions. Similar to Vinyals et al. (2015), this embedding is the input for a LSTM model that generates the output sequence. In ShowAttTell, while the overall architecture is similar to Xu et al. (2015), we adopt the modification suggested by Rennie et al. (2017) and input the attention-derived image features to the cell node of the LSTM. Finally, we use the UpDown model exactly as described in Anderson et al. (2018).

Training and Inference

We perform a two-stage training strategy to train such caption generation models as proposed by Rennie et al. (2017). In the first stage, we train the model to optimize the standard cross-entropy loss. In the second stage, we perform policy gradient with reinforce to optimize the non-differentiable reward function (CIDEr score in our case). During inference, we apply beam search (beam size=2) to decode the caption.

4.3 Caption retrieval models

We define a simple yet powerful retrieval architecture, named TransResNet. It works by projecting the image, personality, and caption in the same space using image, personality, and text encoders.

Image and Personality Encoders

The representation of an image is obtained by using the 2048-dimensional output of the image encoder described in Sec. 4.1

as input to a multi-layer perceptron with ReLU activation units and a final layer of 500 dimensions. To take advantage of personality traits in the

Personality-Captions task, we embed each trait to a 500-dimensional vector to obtain its representation . Image and personality representations are then summed.

Caption Encoders

Each caption is encoded into a vector of the same size using a Transformer architecture (Vaswani et al., 2017), followed by a two layer perceptron. We try two sizes of Transformer: a larger architecture (4 layers, 300 hidden units, 6 attention heads) and a smaller one (2 layers, 300 hidden units, 4 attention heads). We consider either training from scratch or pretraining our models. We either pretrain only the word embeddings, i.e. where we initialize word vectors trained using fastText (Bojanowski et al., 2016) trained on Wikipedia, or pretrain the entire encoder. For the latter, we follow the setup described in Mazaré et al. (2018): we train two encoders on a next-utterance retrieval task on a dataset of dialogs containing 1.7 billion pairs of utterances, where one encodes the context and another the candidates for the next utterance, their dot product indicates the degree of match, and they are trained with negative log-likelihood and -negative sampling. We then initialize our system using the weights of the candidate encoder only, and then train on our task.

For comparison, we also consider a simple bag-of-words encoder (pretrained or not). In this case, is the sum of the 300-dimensional word embeddings of the caption.

In each case, given an input image and personality trait and a candidate caption , the score of the final combination is then computed as .

Figure 2: Our architecture TransResNet, used for our retrieval models.
Training and Inference

Given a pair , and a set of candidates , at inference time the predicted caption is the candidate that maximizes the score . At training time we pass a set of scores through a softmax and train to maximize the log-likelihood of the correct responses. We use mini-batches of 500 training examples; for each example, we use the captions of the other elements of the batch as negatives. Our overall TransResNet architecture is detailed in Figure 2.

5 Experiments

We first test our architectures on traditional caption datasets to assess their ability to factually describe the contents of images in a neutral tone. We then apply the same architectures to Personality-Captions to assess their ability to produce engaging captions conditioned on personality. The latter is tested with both automatic metrics and human evaluation of engagingness.

5.1 Automatic evaluation on Traditional Caption Datasets

Generative Models

For our generative models, we test the quality of our implementations of existing models (ShowTell, ShowAttTell and UpDown) as well as the quality of our image encoders, where we compare ResNet152 and ResNeXt-IG-3.5B. We report performance on the COCO caption dataset (Lin et al., 2014). We evaluate BLEU (Papineni et al., 2002), ROUGE-L (Lin, 2004), CIDEr (Vedantam et al., 2015) and SPICE (Anderson et al., 2016) and compare model’s performances to state-of-the-art models under  Karpathy & Fei-Fei (2015)’s setting.

The results are shown in Table 3. Models trained with ResNeXt-IG-3.5B features consistently outperform their counterparts with ResNet152 features, demonstrating the effectiveness of ResNeXt-IG-3.5B beyond the original image classification and detection results in Mahajan et al. (2018). More importantly, our best model (UpDown) either outperforms or is competitive with state-of-the-art single model performance (Anderson et al., 2018) across most metrics (especially CIDEr).

Image Personality Generated comment
Anxious I love cats but i always get so scared that they will scratch me.
Happy That cat looks SO happy to be outside.
Vague That’s a nice cat. Or is it a lion?
Dramatic That cat looks so angry; it might claw your eyes out!
Charming Awww, sweet kitty. You are so handsome!
Sentimental The arena reminded me of my childhood.
Argumentative I dislike the way the arena has been arranged
Cultured The length of this stadium coincides rather lovely with the width.
Sweet It was such a nice day at the game. These fans are the best.
Romantic Basking at the game with my love
Skeptical So many fireworks, there is no way they set them all off at one
High-spirited Those are the most beautiful fireworks I have ever seen!
Cultured Fireworks have been used in our celebrations for centuries.
Arrogant fireworks are overrated and loud
Humble I’m so grateful for whoever invented fireworks!
Romantic A charming home that will call you back to days gone by.
Anxious This house and this street just makes me feel uneasy.
Creative I could write a novel about this beautiful old home!
Sweet What a cute little neighborhood!
Money-minded Call APR now to get your house renovated!
Table 2: Predictions from our best TransResNet model on the Personality-Captions valid set.
Method Image Encoder BLEU1 BLEU4 ROUGE-L CIDEr SPICE
Adaptive (Lu et al., 2017) ResNet 74.2 32.5 - 108.5 19.5
Att2in (Rennie et al., 2017) ResNet - 33.3 55.3 111.4 -
NBT (Lu et al., 2018) ResNet 75.5 34.7 - 107.2 20.1
UpDown (Anderson et al., 2018) ResNet FRCNN 79.8 36.3 56.9 120.1 21.4
ShowTell (Our) ResNet152 75.2 31.5 54.2 103.9 18.4
ShowAttTell (Our) ResNet152 76.5 32.4 55.1 109.7 19.2
UpDown (Our) ResNet152 77.0 33.9 55.6 112.7 19.6
ShowTell (Our) ResNeXt-IG-3.5B 78.2 35.0 56.6 119.9 20.8
ShowAttTell (Our) ResNeXt-IG-3.5B 78.8 35.6 57.1 121.8 20.6
UpDown (Our) ResNeXt-IG-3.5B 79.3 36.4 57.5 124.0 21.2
Table 3: Generative model performance on COCO caption using the test split of  (Karpathy & Fei-Fei, 2015)
Text Pre- Flickr30k COCO
Model training R@1 R@5 R@10 R@1 R@5 R@10
UVS (Kiros et al., 2014) - 23.0 50.7 62.9 43.4 75.7 85.8
Embedding Net (Wang et al., 2018) - 40.7 69.7 79.2 50.4 79.3 69.4
sm-LSTM (Huang et al., 2016) - 42.5 71.9 81.5 53.2 83.1 91.5
VSE++ (ResNet, FT) (Faghri et al., 2017) - 52.9 80.5 87.2 64.6 90.0 95.7
GXN (i2t+t2i) (Gu et al., 2017) - 56.8 - 89.6 68.5 - 97.9
TransResNet model variants:
 Transformer, ResNet152 Full 10.3 27.3 38.8 21.7 45.6 58.9
 Bag of words ResNeXt-IG-3.5B None 50.0 81.1 90.0 51.6 85.3 93.4
 Transformer ResNeXt-IG-3.5B None 55.6 83.2 90.5 64.0 90.6 96.3
 Bag of words ResNeXt-IG-3.5B Word 58.6 87.2 92.9 54.7 87.1 94.5
 Transformer ResNeXt-IG-3.5B Word 68.4 90.6 95.3 67.3 91.7 96.5
Table 4: Retrieval model performance on Flickr30k and COCO caption using the splits of  (Karpathy & Fei-Fei, 2015). COCO caption performance is measured on the 1k image test split.
Retrieval Models

We compare our retrieval architecture, TransResNet, to existing models reported in the literature on the COCO caption and Flickr30k tasks. We evaluate retrieval metrics R@1, R@5, R@10, and compare our model performance to state-of-the-art models under the setting of (Karpathy & Fei-Fei (2015)). The results are given in Table 4 (for more details, see Tables 7 and 10 in the appendix for COCO and Flickr30k, respectively). For our model, we see large improvements using ResNeXt-IG-3.5B compared to Resnet152, and stronger performance with a Transformer-based text encoding compared to a bag-of-words encoding. Pretraining the text encoder also helps substantially (see Appendix A for more analysis of pretraining of our systems). Our best models are competitive on COCO and are state-of-the-art on Flickr30k by a large margin (68.4 R@1 for our model vs. 56.8 R@1 for the previous state-of-the-art).

5.2 Automatic evaluations on Personality-Captions

Generative models

We first train the aforementioned caption generation models without using the personality traits. This setting is similar to standard image captioning, and Table 5 shows that the three caption generation models that we considered are ranked in the same order, with the UpDown model being the most effective. The best results are again obtained using the ResNeXt-IG-3.5B features. Adding the embedding of the personality trait allows our best model to reach a CIDEr score of 22.0, showing the importance of modeling personality in our new task.

Note that all scores are lower than for the COCO captioning task. Indeed standard image captioning tries to produce text descriptions that are semantically equivalent to the image, whereas Personality-Captions captures how a human responds to a given image when speaking to another human when both can see the image – which is rarely to simply state its contents. Hence, Personality-Captions has intrinsically more diverse outputs, similar to results found in other human communication tasks (Liu et al., 2016). For that reason we perform human evaluation in Section 5.3 in addition to automatic evaluations.

Method Image Encoder Encoder BLEU1 BLEU4 ROUGE-L CIDEr SPICE
ShowTell ResNet152 Yes 12.4 1.4 13.2 14.5 1.6
ShowAttTell ResNet152 Yes 15.3 1.3 13.1 15.2 3.4
UpDown ResNet152 Yes 15.4 1.4 14.6 16.9 4.9
ShowTell ResNeXt-IG-3.5B No 15.2 0.9 13.3 14.4 4.6
ShowAttTell ResNeXt-IG-3.5B No 13.8 0.9 13.1 17.6 5.4
UpDown ResNeXt-IG-3.5B No 14.3 1.0 13.5 18.0 7.0
ShowTell ResNeXt-IG-3.5B Yes 14.2 1.2 14.5 15.4 2.2
ShowAttTell ResNeXt-IG-3.5B Yes 15.0 1.4 14.6 18.8 5.9
UpDown ResNeXt-IG-3.5B Yes 15.6 1.6 15.0 22.0 7.3
Table 5: Generative model caption performance on the Personality-Captions test set.
Retrieval models

Similarly we compare the effect of various configurations of our retrieval model, TransResNet. The models are evaluated in terms of R@1, where for each sample there are 100 candidates to rank: 99 randomly chosen candidates from the test set plus the true label.

Table 6 shows the scores obtained on the test set of Personality-Captions. Again, the impact of using the image encoder trained on billions of images is considerable, we obtain 53.5% for our best ResNeXt-IG-3.5B model, and 34.4% for our best Resnet152 model. Conditioning on the personality traits is also very important (53.5% vs. 38.5% R@1 for the best variants with and without conditioning). Transformer text encoders also outperform bag-of-word embeddings encoders, where pretraining for either type of encoder helps. For Transformers pretraining the whole network performed better than just pretraining the word embeddings, see Appendix A.

Example predictions of our best model, TransResNet (ResNeXt-IG-3.5B), are given in Table 2.

5.3 Human evaluation on Personality-Captions

The goal of Personality-Captions is to be engaging to human readers by emulating human personality traits. We thus test our task and models in a set of human evaluation studies.

Evaluation Setup

Using 500 random images from the YFCC-100M dataset that are not present in Personality-Captions, we obtain captions for them using a variety of methods, as outlined in the sections below, including both human authored captions and model predicted captions. Using a separate set of human annotators, comparisons are then done pairwise: we show each image, with two captions to compare, to five separate annotators and ask them to choose the “more engaging” caption. For experiments where both captions are conditioned on a personality, we show the annotator the personality; otherwise, the personality is hidden. We then report the percentage of the time one method is chosen over the other. The results are summarized in Figure 3.

Figure 3: Human evaluations on Personality-Captions. Engagingness win rates of various pairwise comparisons: human annotations of Personality-Captions vs. traditional captions, vs. Personality-Captions model variants, and models compared against each other.
Text Encoder Pre-training Image Encoder Personality Encoder R@1
Transformer None None Yes 14.5
Transformer Full None Yes 18.1
Transformer Full ResNet152 No 16.6
Bag of Words None ResNet152 Yes 24.2
Transformer None ResNet152 Yes 26.8
Bag of Words Word ResNet152 Yes 28.5
Transformer Full ResNet152 Yes 34.4
Transformer Full ResNeXt-IG-3.5B No 38.5
Bag of Words None ResNeXt-IG-3.5B Yes 38.6
Transformer None ResNeXt-IG-3.5B Yes 42.9
Bag of Words Word ResNeXt-IG-3.5B Yes 45.7
Transformer Full ResNeXt-IG-3.5B Yes 53.5
Table 6: Results for TransResNet retrieval variants on the Personality-Captions test set.
Traditional Human Captions

We compare human authored Personality-Captions captions to human authored traditional neutral (COCO-like) captions. Captions conditioned on a personality were found to be significantly more engaging than those that were neutral captions of the image, with a win rate of 64.5%, which is statistically significant using a binomial two-tailed test.

Human vs. Model Engagingness

We compare the best-performing models from Section 5.2 to human authored Personality-Captions captions. For each test image we condition both human and model on the same (randomly-chosen) personality trait. Our best TransResNet model from Sec. 5.2, using the ResNext-IG-3.5B image features, almost matched human authors, with a win rate of (difference not significant, ). The same model using ResNet152 has a win rate of , showing the importance of strongly performing image features. The best generative model we tried, the UpDown model using ResNext-IG-3.5B image features, performed worse with a win rate of 20.7%, showing the impact of retrieval for engagement.

Model vs. Model engagingness

We also compare our models in a pairwise fashion directly, as measured by human annotators. The results given in Figure 3 (all statistically significant) show the same trends as we observed before: TransResNet with ResNext-IG-3.5B outperforms the same model with ResNet152 features with a win rate of , showing the importance of image features. Additionally, TransResNetwith ResNext-IG-3.5B image features (with no pretraining) also substantially outperforms the UpDown model using ResNext-IG-3.5B with a winrate of .

6 Conclusion

In this work we consider models that can simultaneously understand image content and provide engaging captions for humans. To build strong models, we first leverage the latest advances in image and sentence encoding to create generative and retrieval models that perform well on standard image captioning tasks. In particular, we attain a new state-of-the-art on caption generation on COCO, and introduce a new retrieval architecture, TransResNet, that yields the highest known hits@1 score on the Flickr30k dataset.

To make the models more engaging to humans, we then condition them on a set of controllable personality traits. To that end, we collect a large dataset, Personality-Captions to train such models. Using automatic metrics and human evaluations, we show that our best system is able to produce captions that are close to matching human performance in terms of engagement. We hope our benchmark will encourage further model development, leaving the possibility of superhuman performance coming soon in this domain.


We thank Laurens van der Maaten, Arthur Szlam, Y-Lan Boureau, Pierre-Emmanuel Mazaré, Martin Raison, Alex Lebrun, Emily Dinan, Alexander Miller and Jack Urbanek for advice and discussions.


Appendix A Impact of Pretrained Word Embeddings and Text Encoders

Model Text Encoder Caption retrieval
Pretraining R@1 R@5 R@10 Med Rank
1k Images
m-CNN (Ma et al., 2015) 42.8 - 84.1 2.0
UVS (Kiros et al., 2014) 43.4 75.7 85.8 2.0
HM-LSTM (Niu et al., 2017) 43.9 - 87.8 2.0
Order Embeddings (Vendrov et al., 2015) 46.7 - 88.9 2.0
Embedding Net (Wang et al., 2018) 50.4 79.3 69.4 -
DSPE+Fisher Vector (Wang et al., 2016) 50.1 - 89.2 -
sm-LSTM (Huang et al., 2016) 53.2 83.1 91.5 1.0
VSE++ (ResNet, FT) (Faghri et al., 2017) 64.6 90.0 95.7 1.0
GXN (i2t+t2i) (Gu et al., 2017) 68.5 - 97.9 1.0
Engilberge et al. (2018) 69.8 91.9 96.6 1.0
Transformer, Resnet152 Word 21.7 45.6 58.9 7.0
Bag of words, ResNeXt-IG-3.5B None 51.6 85.3 93.4 1.4
Bag of words, ResNeXt-IG-3.5B Word 54.7 87.1 94.5 1.0
Transformer, ResNeXt-IG-3.5B None 63.4 90.6 96.3 1.0
Transformer, ResNeXt-IG-3.5B Word 66.6 90.6 96.3 1.0
Transformer, ResNeXt-IG-3.5B Full 67.3 91.7 96.5 1.0
5k Images
Order Embeddings (Vendrov et al., 2015) 23.3 - 65.0 5.0
VSE++ (ResNet, FT) (Faghri et al., 2017) 41.3 71.1 81.2 2.0
GXN (i2t+t2i) (Gu et al., 2017) 42.0 - 84.7 2.0
Transformer, Resnet152 Word 7.8 21.9 31.2 30.0
Bag of words, ResNeXt-IG-3.5B None 26.6 58.6 73.0 4.0
Bag of words, ResNeXt-IG-3.5B Word 29.7 62.9 75.7 3.0
Transformer, ResNeXt-IG-3.5B None 38.8 71.6 82.7 2.0
Transformer, ResNeXt-IG-3.5B Word 44 73.7 84 2.0
Transformer, ResNeXt-IG-3.5B Full 44.3 74.5 83.9 2.0
Table 7: More detailed results for retrieval model performance on COCO Captions using the splits of  (Karpathy & Fei-Fei, 2015). For our TransResNet models, we compare two types of pretraining: Full indicates a model with a pretrained text encoder, while Word indicates a model with pretrained word embeddings only.
Model Text Encoder Caption retrieval
Pretraining R@1 R@5 R@10 Med Rank
UVS (Kiros et al., 2014) 23.0 50.7 62.9 5.0
UVS (Github) 29.8 58.4 70.5 4.0
Embedding Net (Wang et al., 2018) 40.7 69.7 79.2 -
DAN (Nam et al., 2016) 41.4 73.5 82.5 2.0
sm-LSTM (Huang et al., 2016) 42.5 71.9 81.5 2.0
2WayNet (Eisenschtat & Wolf, 2016) 49.8 67.5 - -
VSE++ (ResNet, FT) (Faghri et al., 2017) 52.9 80.5 87.2 1.0
DAN (ResNet) (Nam et al., 2016) 55.0 81.8 89.0 1.0
GXN (i2t+t2i) (Gu et al., 2017) 56.8 - 89.6 1.0
Transformer, Resnet152 Word 10.3 27.3 38.8 19
Bag of words, ResNeXt-IG-3.5B None 50.0 81.1 90.0 1.5
Transformer, ResNeXt-IG-3.5B None 55.6 83.2 90.5 1.0
Bag of words, ResNeXt-IG-3.5B Word 58.6 87.2 92.9 1.0
Transformer, ResNeXt-IG-3.5B Full 62.3 88.5 94.4 1.0
Transformer, ResNeXt-IG-3.5B Word 68.4 90.6 95.3 1.0
Table 8: Retrieval model performance on Flickr30k using the splits of  (Karpathy & Fei-Fei, 2015). For our models, we compare two types of pretraining: Full indicates a model with a pretrained text encoder, while Word indicates a model with pretrained word embeddings only.
Method Image Encoder Encoder BLEU1 BLEU4 ROUGE-L CIDEr SPICE
no pretraining:
ShowTell ResNeXt-IG-3.5B Yes 14.2 1.2 14.5 15.4 2.2
ShowAttTell ResNeXt-IG-3.5B Yes 15.0 1.4 14.6 18.8 5.9
UpDown ResNeXt-IG-3.5B Yes 15.6 1.6 15.0 22.0 7.3
with word embedding pretraining:
ShowTell ResNeXt-IG-3.5B Yes 15.6 1.4 14.7 17.0 3.0
ShowAttTell ResNeXt-IG-3.5B Yes 15.0 1.5 14.9 18.5 4.8
UpDown ResNeXt-IG-3.5B Yes 16.4 1.6 15.5 21.5 7.5
Table 9: Comparing Generative model caption performance on the Personality-Captions test set: pretrained word embeddings vs. no pretraining. Pretraining makes a very small impact in this case, unlike in our retrieval models.
Text Encoder
Encoder Type Pretraining Image Encoder Personality Encoder R@1
Transformer Full ResNeXt-IG-3.5B Yes 53.5
Transformer Word ResNeXt-IG-3.5B Yes 48.6
Bag of Words Word ResNeXt-IG-3.5B Yes 45.7
Transformer None ResNeXt-IG-3.5B Yes 42.9
Bag of Words None ResNeXt-IG-3.5B Yes 38.6
Transformer Full ResNeXt-IG-3.5B No 38.5
Transformer Full Resnet152 Yes 34.4
Transformer Word Resnet152 Yes 30.2
Bag of Words Word Resnet152 Yes 28.5
Transformer None Resnet152 Yes 26.8
Bag of Words None Resnet152 Yes 24.2
Transformer Full Resnet152 No 16.6
Table 10: Retrieval model performance on Personality-Captions. We compare two types of pretraining: Full indicates a model with a pretrained text encoder, while Word indicates a model with pretrained word embeddings only.

Appendix B Engaging Captions, with no personality conditioning

Engaging-only Captions

Instead of asking to author a caption based on a personality trait, we can ask humans to simply write an “engaging” caption instead, providing them with no personality cue. We found that human annotators overall preferred captions written by those unconditioned on a personality by a slight margin (). To further understand this difference, we split the images into three subsets based on the personality on which the Personality-Captions annotator conditioned their caption, i.e. whether the personality was positive, negative, or neutral. We then examined the engagingness rates of images for each of these subsets. In the set where Personality-Captions annotators were provided with positive personalities, which totaled 185 out of the 500 images, we found that human annotators preferred the captions conditioned on the personality to those that were not. However, in the other two sets, we found that the unconditioned captions were preferred to the negative or neutral ones. For these two subsets, we believe that, without the context of any personality, annotators may have preferred the inherently more positive caption provided by someone who was asked to be engaging but was not conditioned on a personality.

Type of caption A Win Percentage Type of caption B
Human (all) personality captions 45.5 54.5 Human engaging captions
Human (positive) personality captions 51.2 48.8 Human engaging captions

Table 11: Pairwise win rates of various approaches, evaluated in terms of engagingness
Diversity of captions

We found that the captions written via our method were not only more engaging for positive personality traits, but also resulted in more diversity in terms of personality traits. To measure this diversity, we constructed a model that predicted the personality of a given comment. The classifier consists in the same Transformer as described in 4.3, pre-trained on the same large dialog corpus, followed by a softmax over 215 units. We then compare the total number of personality types as predicted by the classifier among each type of human-labeled data: “engaging” captions conditioned on personalities, “engaging” captions not conditioned on personalities, and traditional image captions. That is, we look at each caption given by the human annotators, assign it a personality via the classifier, and then look at the total set of personalities we have at the end for each set of human-labeled data. For example, out of the 500 human-generated traditional captions, the classifier found of all possible positive personalities in this set of captions. As indicated in Table 12, the human annotators who were assigned a personality produce more diverse captions, particularly negatively and neutrally conditioned ones, as compared to human annotators who are just told to be “engaging” or those who are told to write an image caption.

Annotation Task Personality Trait Coverage
Positive Neutral Negative
Given Personalities 100% 100% 99.0%
Traditional Caption 63.0% 83.3% 47.0%
Engaging, No Conditioning 81.5% 91.7% 71.4%
Personality-Captions 82.7% 94.4% 87.8%
Table 12: Caption diversity in human annotation tasks. Personality-Captions provides more diverse personality traits than traditional captions or collecting engaging captions without specifying a personality trait to the annotator, as measured by a personality trait classifier.

Appendix C Comparing Generative and Retrieval Models on COCO

The ultimate test of our generative and retrieval models on Personality-Captions is performed using human evaluations. Comparing them using automatic metrics is typically difficult because retrieval methods perform well with ranking metrics they are optimized for and generative models perform well with word overlap metrics they are optimized for, but neither of these necessarily correlate with human judgements, see e.g. Zhang et al. (2018).

Nevertheless, here we compare our generative and retrieval models directly with automatic metrics on COCO. We computed the BLEU, CIDEr, SPICE, and ROUGE-L scores for our best TransResNet model. The comparison is given in Table 13.

TransResNet 50.6 10.9 38.0 49.1 13.9
ShowTell 78.2 35.0 56.6 119.9 20.8
ShowAttTell 78.8 35.6 57.1 121.8 20.6
UpDown 79.3 36.4 57.5 124.0 21.2
Table 13: Generative and retrieval model performance on COCO caption using the test split of  (Karpathy & Fei-Fei, 2015). All models use ResNeXt-IG-3.5B image features.

Appendix D Human Annotation Setup

Instructions for the annotation task collecting the data for Personality-Captions.

Appendix E Samples from Personality-Captions

Sarcastic Mellow Zany
Yes please sit by me Look at that smooth easy catch of the ball. like ballet. I wish I could just run down this shore!
Contradictory Contemptible Energetic
Love what you did with the place! I can’t believe no one has been taking care of this plant. Terrible About to play the best tune you’ve ever heard in your life. Get ready!
Kind Spirited Creative
they left me a parking spot That is one motor cycle enthusiast!!! Falck alarm, everyone. Just a Falck alarm.
Crazy Morbid Questioning
I drove down this road backwards at 90 miles per hour three times I hope this car doesn’t get into a wreck. Why do people think its cool to smoke cigarettes?
Table 14: Some samples from Personality-Captions. For each sample we asked a person to write a caption that fits both the image and the personality.

Appendix F Examples from Human Evaluation Set

center=10.5cm Image and Pers. Use pers. Captioning Caption No Standard A city on the background, a lake on the front, during a sunset. No Engaging Talk about summer fun! Can I join? :) Yes Human i feel moved by the sunset Yes TransResNet The water at night is a beautiful sight. Spirited Yes UpDown This is a beautiful sunset! No Standard Rose colored soft yarn. No Engaging I really want to untangle that yarn. Yes Human I cannot believe how yummy that looks. Yes TransResNet What is up with all the knitting on my feed Ridiculous Yes UpDown I would love to be a of that fruit! No Standard A beautiful mesa town built into the cliffs. No Engaging That is a strange cave Yes Human It must be very dangerous if children play there Yes TransResNet I hope my kids don’t climb on this. Maternal Yes UpDown I hope this is a beautiful place. No Standard Hockey players competing for control of the hockey puck. No Engaging Great save, goalie!! Yes Human Hockey is a little too barbaric for my taste. Yes TransResNet Hockey players gracefully skate across the ice. Sophisticated Yes UpDown This hockey is like they are a great of the game. No Standard two people walking through a snowy forest. No Engaging Too cold for me. Yes Human I wonder what’s at the finish line for these guys? Yes TransResNet I wonder why they are running. Curious Yes UpDown I wonder what they are a? No Standard Hollywood Tower at Night No Engaging I went to that theme park, but was too scared to get on that ride! Yes Human I am so excited to be here! Yes TransResNet I remember going to disney world, it was one of the best trips I’ve ever done. Happy Yes UpDown This looks like a beautiful view!

Table 15: Example variants of the captions shown to human annotators in the human evaluation tasks in Section 5.3. The first two captions are human annotations not conditioned on a personality; the next three are captions conditioned on the listed personality, and are generated via a human annotator, TransResNet, and UpDown respectively.

Appendix G More examples from TransResNet

center=10.5cm Image Personality Generated comment Sweet I love, love, love these chairs! I want the big one in my house! Vague This chair is either covered in snow or the snow is covered in the chair. Cultured These chairs remind me of the Swedish interior design revolution of the 70’s. Paranoid What if someone fell off those chairs. Overimaginative Those chairs look like they could be in a doll house. Arrogant I’ve seen better sunsets elsewhere. Overimaginative that sunset is so orange it could be a fruit Vague It’s the sunset. Optimistic The sunset makes look forward to a happy tomorrow. Charming The way the sun is hitting the water makes for a romantic evening. Sweet What a cute puppy, reminds me of my friends. Skeptical I don’t think this dog will bite me. Sympathetic poor dog! It looks so hungry :c Vague it’s a dog Wishful I wish that I had a dog as cute as him. Cultured I love a cultural celebration. Skeptical I’m not sure if these are guys in costumes or time travelers. Sweet I love that they are celebrating their traditions and culture. Overimaginative They look like they could be dancers in a fantasy movie with dragons! Sympathetic I feel sorry for him having to wear that Romantic If I was an insect, I would definitely make this my mate. Humble I am grateful that spiders eat these disgusting bugs. Paranoid What is going on? Are these insects dangerous? Creative I made something like this from colored toothpicks once Money-minded how much are those? those looks expensive Happy That is so cool! I I love street art! Optimistic The future is bright for people who can dream in artistic ways. Critical I do believe this taggers verbage is a tad junvenile Charming What a charming wall. Adventurous I think I could create art like that, I will go learn and take action. Dramatic The color of this flower is absolutely astounding. I can’t believe it. Wishful I always wish I could grow these types of flowers. Sweet Beautiful flowers! I would give them to you. Romantic The pink flowers would make a beautiful bouquet for my wife. Happy Oh my, what a lovely purple color of nature’s new sprouts!

Table 16: More example predictions from our best TransResNet model on the Personality-Captions validation set.

center=10.5cm Image Personality Generated comment Adventurous This biking event looks like something that I would try! Vague Those people are riding a bike. Charming I bet a wonderful couple uses this bike to tour the countryside together. Optimistic A hopeful cyclist trying to catch up to the pack Paranoid What if all those bikes just tipped over! Adventurous I am so ready for the conference. Cultured This conference is one of the most important ones in the country. Vague The organization on that table is uncertain. Dramatic OMG!! This ceremony is frightening! Sympathetic I feel bad for these people being so cramped in this room. Old-fashioned Such old fashioned script, a true lost art. Charming I could use these to write to my loved ones. Argumentative Can you even read this through all the jpeg artifacts? Anxious I hope this paper doesnt tear, history will be destroyed. Dramatic Some of the most profound things ever written have been on linen. Happy It finally snowed, it makes me feel awesome Wishful I wish there was enough for snow angels. Boyish Can I go sledding now? Romantic What a beautiful frost! Looks like the perfect place to fall in love! Cultured The white of the snow provides a glistening contrast to the dead trees. Wishful I wish I could have a life as easy as a plant. Money-minded

This plant is probably worth a lot of money

Critical the leaf is ruining the picture Humble This plant is a symbol of life in humble opinion. Just gorgeous! Paranoid If you eat this leaf it definetly will not poison you. Or will it… Romantic This valentine concert is for lovers. Boyish It’s always fun to get down and jam with the boys! Creative musician performing a song of theirs Sweet oh what lovely young musicians Money-minded I wonder how much the musicians have in student loan debt. Skeptical I wonder why the ships are all parked further down the deck. Paranoid I hope those ships don’t sink Happy Look how beautiful the port is at this time of day! :) Arrogant Those boats don’t need to be docked at this time of night Humble We are so lucky to have these boats available locally

Table 17: More example predictions from our best TransResNet model on the Personality-Captions validation set.