How would your summer season vacation’s pictures look had Edvard Munch painted them? (Maybe it’s higher to not know).
Let’s take a extra comforting instance: How would a pleasant, summarly river panorama look if painted by Katsushika Hokusai?
Fashion switch on photos isn’t new, however acquired a lift when Gatys, Ecker, and Bethge(Gatys, Ecker, and Bethge 2015) confirmed learn how to efficiently do it with deep studying.
The primary thought is easy: Create a hybrid that may be a tradeoff between the content material picture we need to manipulate, and a type picture we need to imitate, by optimizing for maximal resemblance to each on the identical time.
If you happen to’ve learn the chapter on neural type switch from Deep Studying with R, chances are you’ll acknowledge a few of the code snippets that observe.
Nevertheless, there is a vital distinction: This publish makes use of TensorFlow Keen Execution, permitting for an crucial approach of coding that makes it straightforward to map ideas to code.
Identical to earlier posts on keen execution on this weblog, this can be a port of a Google Colaboratory pocket book that performs the identical activity in Python.
As common, please be sure you have the required bundle variations put in. And no want to repeat the snippets – you’ll discover the entire code among the many Keras examples.
Conditions
The code on this publish will depend on the newest variations of a number of of the TensorFlow R packages. You possibly can set up these packages as follows:
set up.packages(c("tensorflow", "keras", "tfdatasets"))You must also ensure that you’re operating the very newest model of TensorFlow (v1.10), which you’ll set up like so:
library(tensorflow)
install_tensorflow()There are extra necessities for utilizing TensorFlow keen execution. First, we have to name tfe_enable_eager_execution() proper originally of this system. Second, we have to use the implementation of Keras included in TensorFlow, quite than the bottom Keras implementation.
Conditions behind us, let’s get began!
Enter photos
Right here is our content material picture – exchange by a picture of your personal:
# In case you have sufficient reminiscence in your GPU, no must load the photographs
# at such small measurement.
# That is the dimensions I discovered working for a 4G GPU.
img_shape <- c(128, 128, 3)
content_path <- "isar.jpg"
content_image <- image_load(content_path, target_size = img_shape[1:2])
content_image %>%
image_to_array() %>%
`/`(., 255) %>%
as.raster() %>%
plot()
And right here’s the type mannequin, Hokusai’s The Nice Wave off Kanagawa, which you’ll obtain from Wikimedia Commons:
We create a wrapper that masses and preprocesses the enter photos for us.
As we will probably be working with VGG19, a community that has been educated on ImageNet, we have to rework our enter photos in the identical approach that was used coaching it. Later, we’ll apply the inverse transformation to our mixture picture earlier than displaying it.
load_and_preprocess_image <- perform(path) {
img <- image_load(path, target_size = img_shape[1:2]) %>%
image_to_array() %>%
k_expand_dims(axis = 1) %>%
imagenet_preprocess_input()
}
deprocess_image <- perform(x) {
x <- x[1, , ,]
# Take away zero-center by imply pixel
x[, , 1] <- x[, , 1] + 103.939
x[, , 2] <- x[, , 2] + 116.779
x[, , 3] <- x[, , 3] + 123.68
# 'BGR'->'RGB'
x <- x[, , c(3, 2, 1)]
x[x > 255] <- 255
x[x < 0] <- 0
x[] <- as.integer(x) / 255
x
}Setting the scene
We’re going to use a neural community, however we received’t be coaching it. Neural type switch is a bit unusual in that we don’t optimize the community’s weights, however again propagate the loss to the enter layer (the picture), as a way to transfer it within the desired course.
We will probably be considering two sorts of outputs from the community, similar to our two objectives.
Firstly, we need to preserve the mix picture much like the content material picture, on a excessive stage. In a convnet, higher layers map to extra holistic ideas, so we’re selecting a layer excessive up within the graph to check outputs from the supply and the mix.
Secondly, the generated picture ought to “appear like” the type picture. Fashion corresponds to decrease stage options like texture, shapes, strokes… So to check the mix in opposition to the type instance, we select a set of decrease stage conv blocks for comparability and mixture the outcomes.
content_layers <- c("block5_conv2")
style_layers <- c("block1_conv1",
"block2_conv1",
"block3_conv1",
"block4_conv1",
"block5_conv1")
num_content_layers <- size(content_layers)
num_style_layers <- size(style_layers)
get_model <- perform() {
vgg <- application_vgg19(include_top = FALSE, weights = "imagenet")
vgg$trainable <- FALSE
style_outputs <- map(style_layers, perform(layer) vgg$get_layer(layer)$output)
content_outputs <- map(content_layers, perform(layer) vgg$get_layer(layer)$output)
model_outputs <- c(style_outputs, content_outputs)
keras_model(vgg$enter, model_outputs)
}Losses
When optimizing the enter picture, we’ll take into account three kinds of losses. Firstly, the content material loss: How completely different is the mix picture from the supply? Right here, we’re utilizing the sum of the squared errors for comparability.
content_loss <- perform(content_image, goal) {
k_sum(k_square(goal - content_image))
}Our second concern is having the kinds match as intently as doable. Fashion is often operationalized because the Gram matrix of flattened characteristic maps in a layer. We thus assume that type is said to how maps in a layer correlate with different.
We due to this fact compute the Gram matrices of the layers we’re considering (outlined above), for the supply picture in addition to the optimization candidate, and evaluate them, once more utilizing the sum of squared errors.
gram_matrix <- perform(x) {
options <- k_batch_flatten(k_permute_dimensions(x, c(3, 1, 2)))
gram <- k_dot(options, k_transpose(options))
gram
}
style_loss <- perform(gram_target, mixture) {
gram_comb <- gram_matrix(mixture)
k_sum(k_square(gram_target - gram_comb)) /
(4 * (img_shape[3] ^ 2) * (img_shape[1] * img_shape[2]) ^ 2)
}Thirdly, we don’t need the mix picture to look overly pixelated, thus we’re including in a regularization part, the whole variation within the picture:
total_variation_loss <- perform(picture) {
y_ij <- picture[1:(img_shape[1] - 1L), 1:(img_shape[2] - 1L),]
y_i1j <- picture[2:(img_shape[1]), 1:(img_shape[2] - 1L),]
y_ij1 <- picture[1:(img_shape[1] - 1L), 2:(img_shape[2]),]
a <- k_square(y_ij - y_i1j)
b <- k_square(y_ij - y_ij1)
k_sum(k_pow(a + b, 1.25))
}The tough factor is learn how to mix these losses. We’ve reached acceptable outcomes with the next weightings, however be happy to mess around as you see match:
content_weight <- 100
style_weight <- 0.8
total_variation_weight <- 0.01Get mannequin outputs for the content material and elegance photos
We want the mannequin’s output for the content material and elegance photos, however right here it suffices to do that simply as soon as.
We concatenate each photos alongside the batch dimension, go that enter to the mannequin, and get again an inventory of outputs, the place each ingredient of the checklist is a 4-d tensor. For the type picture, we’re within the type outputs at batch place 1, whereas for the content material picture, we want the content material output at batch place 2.
Within the beneath feedback, please notice that the sizes of dimensions 2 and three will differ in the event you’re loading photos at a unique measurement.
get_feature_representations <-
perform(mannequin, content_path, style_path) {
# dim == (1, 128, 128, 3)
style_image <-
load_and_process_image(style_path) %>% k_cast("float32")
# dim == (1, 128, 128, 3)
content_image <-
load_and_process_image(content_path) %>% k_cast("float32")
# dim == (2, 128, 128, 3)
stack_images <- k_concatenate(checklist(style_image, content_image), axis = 1)
# size(model_outputs) == 6
# dim(model_outputs[[1]]) = (2, 128, 128, 64)
# dim(model_outputs[[6]]) = (2, 8, 8, 512)
model_outputs <- mannequin(stack_images)
style_features <-
model_outputs[1:num_style_layers] %>%
map(perform(batch) batch[1, , , ])
content_features <-
model_outputs[(num_style_layers + 1):(num_style_layers + num_content_layers)] %>%
map(perform(batch) batch[2, , , ])
checklist(style_features, content_features)
}Computing the losses
On each iteration, we have to go the mix picture by the mannequin, get hold of the type and content material outputs, and compute the losses. Once more, the code is extensively commented with tensor sizes for simple verification, however please remember that the precise numbers presuppose you’re working with 128×128 photos.
compute_loss <-
perform(mannequin, loss_weights, init_image, gram_style_features, content_features) {
c(style_weight, content_weight) %<-% loss_weights
model_outputs <- mannequin(init_image)
style_output_features <- model_outputs[1:num_style_layers]
content_output_features <-
model_outputs[(num_style_layers + 1):(num_style_layers + num_content_layers)]
# type loss
weight_per_style_layer <- 1 / num_style_layers
style_score <- 0
# dim(style_zip[[5]][[1]]) == (512, 512)
style_zip <- transpose(checklist(gram_style_features, style_output_features))
for (l in 1:size(style_zip)) {
# for l == 1:
# dim(target_style) == (64, 64)
# dim(comb_style) == (1, 128, 128, 64)
c(target_style, comb_style) %<-% style_zip[[l]]
style_score <- style_score + weight_per_style_layer *
style_loss(target_style, comb_style[1, , , ])
}
# content material loss
weight_per_content_layer <- 1 / num_content_layers
content_score <- 0
content_zip <- transpose(checklist(content_features, content_output_features))
for (l in 1:size(content_zip)) {
# dim(comb_content) == (1, 8, 8, 512)
# dim(target_content) == (8, 8, 512)
c(target_content, comb_content) %<-% content_zip[[l]]
content_score <- content_score + weight_per_content_layer *
content_loss(comb_content[1, , , ], target_content)
}
# whole variation loss
variation_loss <- total_variation_loss(init_image[1, , ,])
style_score <- style_score * style_weight
content_score <- content_score * content_weight
variation_score <- variation_loss * total_variation_weight
loss <- style_score + content_score + variation_score
checklist(loss, style_score, content_score, variation_score)
}Computing the gradients
As quickly as now we have the losses, acquiring the gradients of the general loss with respect to the enter picture is only a matter of calling tape$gradient on the GradientTape. Be aware that the nested name to compute_loss, and thus the decision of the mannequin on our mixture picture, occurs contained in the GradientTape context.
compute_grads <-
perform(mannequin, loss_weights, init_image, gram_style_features, content_features) {
with(tf$GradientTape() %as% tape, {
scores <-
compute_loss(mannequin,
loss_weights,
init_image,
gram_style_features,
content_features)
})
total_loss <- scores[[1]]
checklist(tape$gradient(total_loss, init_image), scores)
}Coaching section
Now it’s time to coach! Whereas the pure continuation of this sentence would have been “… the mannequin,” the mannequin we’re coaching right here isn’t VGG19 (that one we’re simply utilizing as a device), however a minimal setup of simply:
- a
Variablethat holds our to-be-optimized picture - the loss capabilities we outlined above
- an optimizer that can apply the calculated gradients to the picture variable (
tf$prepare$AdamOptimizer)
Beneath, we get the type options (of the type picture) and the content material characteristic (of the content material picture) simply as soon as, then iterate over the optimization course of, saving the output each 100 iterations.
In distinction to the unique article and the Deep Studying with R e book, however following the Google pocket book as a substitute, we’re not utilizing L-BFGS for optimization, however Adam, as our objective right here is to supply a concise introduction to keen execution.
Nevertheless, you possibly can plug in one other optimization methodology in the event you needed, changing
optimizer$apply_gradients(checklist(tuple(grads, init_image)))
by an algorithm of your selection (and naturally, assigning the results of the optimization to the Variable holding the picture).
run_style_transfer <- perform(content_path, style_path) {
mannequin <- get_model()
stroll(mannequin$layers, perform(layer) layer$trainable = FALSE)
c(style_features, content_features) %<-%
get_feature_representations(mannequin, content_path, style_path)
# dim(gram_style_features[[1]]) == (64, 64)
gram_style_features <- map(style_features, perform(characteristic) gram_matrix(characteristic))
init_image <- load_and_process_image(content_path)
init_image <- tf$contrib$keen$Variable(init_image, dtype = "float32")
optimizer <- tf$prepare$AdamOptimizer(learning_rate = 1,
beta1 = 0.99,
epsilon = 1e-1)
c(best_loss, best_image) %<-% checklist(Inf, NULL)
loss_weights <- checklist(style_weight, content_weight)
start_time <- Sys.time()
global_start <- Sys.time()
norm_means <- c(103.939, 116.779, 123.68)
min_vals <- -norm_means
max_vals <- 255 - norm_means
for (i in seq_len(num_iterations)) {
# dim(grads) == (1, 128, 128, 3)
c(grads, all_losses) %<-% compute_grads(mannequin,
loss_weights,
init_image,
gram_style_features,
content_features)
c(loss, style_score, content_score, variation_score) %<-% all_losses
optimizer$apply_gradients(checklist(tuple(grads, init_image)))
clipped <- tf$clip_by_value(init_image, min_vals, max_vals)
init_image$assign(clipped)
end_time <- Sys.time()
if (k_cast_to_floatx(loss) < best_loss) {
best_loss <- k_cast_to_floatx(loss)
best_image <- init_image
}
if (i %% 50 == 0) {
glue("Iteration: {i}") %>% print()
glue(
"Complete loss: {k_cast_to_floatx(loss)},
type loss: {k_cast_to_floatx(style_score)},
content material loss: {k_cast_to_floatx(content_score)},
whole variation loss: {k_cast_to_floatx(variation_score)},
time for 1 iteration: {(Sys.time() - start_time) %>% spherical(2)}"
) %>% print()
if (i %% 100 == 0) {
png(paste0("style_epoch_", i, ".png"))
plot_image <- best_image$numpy()
plot_image <- deprocess_image(plot_image)
plot(as.raster(plot_image), foremost = glue("Iteration {i}"))
dev.off()
}
}
}
glue("Complete time: {Sys.time() - global_start} seconds") %>% print()
checklist(best_image, best_loss)
}Able to run
Now, we’re prepared to start out the method:
c(best_image, best_loss) %<-% run_style_transfer(content_path, style_path)In our case, outcomes didn’t change a lot after ~ iteration 1000, and that is how our river panorama was wanting:
… undoubtedly extra inviting than had it been painted by Edvard Munch!
Conclusion
With neural type switch, some fiddling round could also be wanted till you get the outcome you need. However as our instance reveals, this doesn’t imply the code must be sophisticated. Moreover to being straightforward to know, keen execution additionally enables you to add debugging output, and step by the code line-by-line to verify on tensor shapes.
Till subsequent time in our keen execution collection!