Brief Review — GAN-CLS-INT: Generative Adversarial Text to Image Synthesis
Proposes Matching-Aware Discriminator (GAN-CLS), Learning with Manifold Interpolation (GAN-INT), & Combined One (GAN-CLS-INT)
Generative Adversarial Network (GAN)
Image Synthesis: 2014 … 2019 [SAGAN]
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- A novel deep architecture and GAN formulation are proposed to effectively bridge these advances in text and image modeling, translating visual concepts from characters to pixels.
1. Proposed GAN for Text to Image Synthesis
- In the generator G, the noise prior z is first sampled. The text query t using text encoder φ, then concatenated to the noise vector z. A synthetic image ^x is generated.
- In the discriminator D, at the near end, the description embedding is replicated spatially and a depth concatenation is performed.
1.1. Matching-Aware Discriminator (GAN-CLS)
- In naive GAN, the discriminator observes two kinds of inputs: real images with matching text, and synthetic images with arbitrary text. Therefore, it must implicitly separate two sources of error: unrealistic images (for any text), and realistic images of the wrong class that mismatch the conditioning information.
- Based on the intuition that this may complicate learning dynamics, the GAN training algorithm is modified to separate these error sources.
A third type of input is added, which consists of real images with mismatched text, which the discriminator must learn to score as fake, i.e. code line 8 as shown in the Algorithm 1 above.
1.2. Learning With Manifold Interpolation (GAN-INT)
A large amount of additional text embeddings can be generated by simply interpolating between embeddings of training set captions.
- Critically, these interpolated text embeddings need not correspond to any actual human-written text, so there is no additional labeling cost.
- This can be viewed as adding an additional term to the generator objective to minimize:
- β=0.5 works well.
And GAN-INT can be combined with GAN-CLS as GAN-CLS-INT.
1.3. Inverting the Generator for Style Transfer
If the text encoding φ(t) captures the image content (e.g. flower shape and colors), then in order to generate a realistic image the noise sample z should capture style factors such as background color and pose. With a trained GAN, one may wish to transfer the style of a query image onto the content of a particular text description.
- To achieve this, one can train a convolutional network to invert G to regress from samples ^x ← G(z, φ(t)) back onto z. A simple squared loss is used to train the style encoder:
- where S is the style encoder network.
- With a trained generator and style encoder, style transfer from a query image x onto text t proceeds as follows:
- where ^x is the result image and s is the predicted style.
2.1. Bird Images
GAN and GAN-CLS get some color information right, but the images do not look real. However, GAN-INT and GAN-INT-CLS show plausible images that usually match all or at least part of the caption.
2.2. Flower Images
- All four methods can generate plausible flower images that match the description. Maybe this dataset is easier.
2.3. Interpolating Two Sentences
Interpolations can accurately reflect color information, such as a bird changing from blue to red while the pose and background are invariant.
2.4. Style Transfer
Style transfer preserves detailed background information such as a tree branch upon which the bird is perched.