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Ensure 16-bit input images embed onto alpha background

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Support gamma correction of images with alpha channel
Favour shrink over affine when reducing by integral factor
This commit is contained in:
Lovell Fuller
2016-01-30 22:23:17 +00:00
parent 41e50770d1
commit 2675b2265b
10 changed files with 70 additions and 15 deletions
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28
src/pipeline.cc
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@@ -43,6 +43,7 @@ using vips::VError;
using sharp::Composite;
using sharp::Normalize;
using sharp::Gamma;
using sharp::Blur;
using sharp::Sharpen;
@@ -425,7 +426,8 @@ class PipelineWorker : public AsyncWorker {
}
// Calculate maximum alpha value based on input image pixel depth
double maxAlpha = (image.format() == VIPS_FORMAT_USHORT) ? 65535.0 : 255.0;
bool is16Bit = (image.format() == VIPS_FORMAT_USHORT);
double maxAlpha = is16Bit ? 65535.0 : 255.0;
// Flatten image to remove alpha channel
if (baton->flatten && HasAlpha(image)) {
@@ -449,8 +451,8 @@ class PipelineWorker : public AsyncWorker {
}
// Gamma encoding (darken)
if (baton->gamma >= 1 && baton->gamma <= 3 && !HasAlpha(image)) {
image = image.gamma(VImage::option()->set("exponent", 1.0 / baton->gamma));
if (baton->gamma >= 1 && baton->gamma <= 3) {
image = Gamma(image, 1.0 / baton->gamma);
}
// Convert to greyscale (linear, therefore after gamma encoding, if any)
@@ -541,10 +543,6 @@ class PipelineWorker : public AsyncWorker {
// Crop/embed
if (image.width() != baton->width || image.height() != baton->height) {
if (baton->canvas == Canvas::EMBED) {
// Add non-transparent alpha channel, if required
if (baton->background[3] < 255.0 && !HasAlpha(image)) {
image = image.bandjoin(VImage::black(image.width(), image.height()).invert());
}
// Scale up 8-bit values to match 16-bit input image
double multiplier = (image.interpretation() == VIPS_INTERPRETATION_RGB16) ? 256.0 : 1.0;
// Create background colour
@@ -557,6 +555,12 @@ class PipelineWorker : public AsyncWorker {
if (baton->background[3] < 255.0 || HasAlpha(image)) {
background.push_back(baton->background[3] * multiplier);
}
// Add non-transparent alpha channel, if required
if (baton->background[3] < 255.0 && !HasAlpha(image)) {
VImage alpha = VImage::new_matrix(image.width(), image.height())
.new_from_image(baton->background[3] * multiplier);
image = image.bandjoin(alpha);
}
// Embed
int left = static_cast<int>(round((baton->width - image.width()) / 2));
int top = static_cast<int>(round((baton->height - image.height()) / 2));
@@ -639,11 +643,17 @@ class PipelineWorker : public AsyncWorker {
// Reverse premultiplication after all transformations:
if (shouldPremultiplyAlpha) {
image = image.unpremultiply(VImage::option()->set("max_alpha", maxAlpha));
// Cast pixel values to integer
if (is16Bit) {
image = image.cast(VIPS_FORMAT_USHORT);
} else {
image = image.cast(VIPS_FORMAT_UCHAR);
}
}
// Gamma decoding (brighten)
if (baton->gamma >= 1 && baton->gamma <= 3 && !HasAlpha(image)) {
image = image.gamma(VImage::option()->set("exponent", baton->gamma));
if (baton->gamma >= 1 && baton->gamma <= 3) {
image = Gamma(image, baton->gamma);
}
// Apply normalization - stretch luminance to cover full dynamic range