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?
Model switch on photos is just not new, however acquired a lift when Gatys, Ecker, and Bethge(Gatys, Ecker, and Bethge 2015) confirmed how you can efficiently do it with deep studying.
The principle thought is easy: Create a hybrid that may be a tradeoff between the content material picture we wish to manipulate, and a type picture we wish to imitate, by optimizing for maximal resemblance to each on the identical time.
When you’ve learn the chapter on neural type switch from Deep Studying with R, it’s possible you’ll acknowledge a number of the code snippets that observe.
Nevertheless, there is a crucial distinction: This publish makes use of TensorFlow Keen Execution, permitting for an crucial approach of coding that makes it simple to map ideas to code.
Similar to earlier posts on keen execution on this weblog, it is a port of a Google Colaboratory pocket book that performs the identical process in Python.
As common, please be sure to have the required package deal 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 is determined by the newest variations of a number of of the TensorFlow R packages. You may set up these packages as follows:
set up.packages(c("tensorflow", "keras", "tfdatasets"))You also needs to make sure that you might be 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 initially of this system. Second, we have to use the implementation of Keras included in TensorFlow, somewhat 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 individual:
# In case you have sufficient reminiscence in your GPU, no must load the photographs
# at such small dimension.
# That is the scale 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 Kanagawawhich you’ll obtain from Wikimedia Commons:
style_path <- "The_Great_Wave_off_Kanagawa.jpg"
style_image <- image_load(content_path, target_size = img_shape(1:2))
style_image %>%
image_to_array() %>%
`/`(., 255) %>%
as.raster() %>%
plot()
We create a wrapper that masses and preprocesses the enter photos for us.
As we will likely be working with VGG19, a community that has been skilled 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 <- operate(path) {
img <- image_load(path, target_size = img_shape(1:2)) %>%
image_to_array() %>%
k_expand_dims(axis = 1) %>%
imagenet_preprocess_input()
}
deprocess_image <- operate(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), with a view to transfer it within the desired route.
We will likely be serious about two sorts of outputs from the community, akin to our two targets.
Firstly, we wish to maintain the mixture picture much like the content material picture, on a excessive stage. In a convnet, higher layers map to extra holistic ideas, so we’re choosing a layer excessive up within the graph to check outputs from the supply and the mixture.
Secondly, the generated picture ought to “appear like” the type picture. Model corresponds to decrease stage options like texture, shapes, strokes… So to check the mixture in opposition to the type instance, we select a set of decrease stage conv blocks for comparability and combination 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 <- operate() {
vgg <- application_vgg19(include_top = FALSE, weights = "imagenet")
vgg$trainable <- FALSE
style_outputs <- map(style_layers, operate(layer) vgg$get_layer(layer)$output)
content_outputs <- map(content_layers, operate(layer) vgg$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 varieties of losses. Firstly, the content material loss: How totally different is the mixture picture from the supply? Right here, we’re utilizing the sum of the squared errors for comparability.
content_loss <- operate(content_image, goal) {
k_sum(k_square(goal - content_image))
}Our second concern is having the types match as intently as attainable. Model is usually operationalized because the Gram matrix of flattened function maps in a layer. We thus assume that type is expounded to how maps in a layer correlate with different.
We subsequently compute the Gram matrices of the layers we’re serious about (outlined above), for the supply picture in addition to the optimization candidate, and examine them, once more utilizing the sum of squared errors.
gram_matrix <- operate(x) {
options <- k_batch_flatten(k_permute_dimensions(x, c(3, 1, 2)))
gram <- k_dot(options, k_transpose(options))
gram
}
style_loss <- operate(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 mixture picture to look overly pixelated, thus we’re including in a regularization part, the whole variation within the picture:
total_variation_loss <- operate(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 how you can 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’d like 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, cross that enter to the mannequin, and get again a listing 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’d like the content material output at batch place 2.
Within the under feedback, please be aware that the sizes of dimensions 2 and three will differ in the event you’re loading photos at a distinct dimension.
get_feature_representations <-
operate(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(operate(batch) batch(1, , , ))
content_features <-
model_outputs((num_style_layers + 1):(num_style_layers + num_content_layers)) %>%
map(operate(batch) batch(2, , , ))
checklist(style_features, content_features)
}Computing the losses
On each iteration, we have to cross the mixture picture via the mannequin, receive 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 needless to say the precise numbers presuppose you’re working with 128×128 photos.
compute_loss <-
operate(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)
}
# complete 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 we’ve got the losses, acquiring the gradients of the general loss with respect to the enter picture is only a matter of calling tape$gradient on the GradientTape. Be aware that the nested name to compute_lossand thus the decision of the mannequin on our mixture picture, occurs contained in the GradientTape context.
compute_grads <-
operate(mannequin, loss_weights, init_image, gram_style_features, content_features) {
with(tf$GradientTape() %as% tape, {
scores <-
compute_loss(mannequin,
loss_weights,
init_image,
gram_style_features,
content_features)
})
total_loss <- scores((1))
checklist(tape$gradient(total_loss, init_image), scores)
}Coaching section
Now it’s time to coach! Whereas the pure continuation of this sentence would have been “… the mannequin,” the mannequin we’re coaching right here is just not VGG19 (that one we’re simply utilizing as a software), however a minimal setup of simply:
- a
Variablethat holds our to-be-optimized picture - the loss features we outlined above
- an optimizer that may apply the calculated gradients to the picture variable (
tf$practice$AdamOptimizer)
Under, we get the type options (of the type picture) and the content material function (of the content material picture) simply as soon as, then iterate over the optimization course of, saving the output each 100 iterations.
In distinction to the unique article and the Deep Studying with R e book, however following the Google pocket book as an alternative, we’re not utilizing L-BFGS for optimization, however Adam, as our objective right here is to supply a concise introduction to keen execution.
Nevertheless, you possibly can plug in one other optimization methodology in the event you wished, changing
optimizer$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 <- operate(content_path, style_path) {
mannequin <- get_model()
stroll(mannequin$layers, operate(layer) layer$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, operate(function) gram_matrix(function))
init_image <- load_and_process_image(content_path)
init_image <- tf$contrib$keen$Variable(init_image, dtype = "float32")
optimizer <- tf$practice$AdamOptimizer(learning_rate = 1,
beta1 = 0.99,
epsilon = 1e-1)
c(best_loss, best_image) %<-% checklist(Inf, NULL)
loss_weights <- checklist(style_weight, content_weight)
start_time <- Sys.time()
global_start <- Sys.time()
norm_means <- c(103.939, 116.779, 123.68)
min_vals <- -norm_means
max_vals <- 255 - norm_means
for (i in seq_len(num_iterations)) {
# dim(grads) == (1, 128, 128, 3)
c(grads, all_losses) %<-% compute_grads(mannequin,
loss_weights,
init_image,
gram_style_features,
content_features)
c(loss, style_score, content_score, variation_score) %<-% all_losses
optimizer$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)},
complete 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), essential = 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 begin 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 needs to be sophisticated. Moreover to being simple to understand, keen execution additionally enables you to add debugging output, and step via the code line-by-line to examine on tensor shapes.
Till subsequent time in our keen execution collection!
Gatys, Leon A., Alexander S. Ecker, and Matthias Bethge. 2015. “A Neural Algorithm of Creative Model.” CoRR abs/1508.06576. http://arxiv.org/abs/1508.06576.
