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Avoid (un)premultiplication for overlay image without alpha channel

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Add 'premultiplied' boolean attribute to output info, helps test
This commit is contained in:
Lovell Fuller
2017-03-25 16:52:09 +00:00
parent 301bfbd271
commit 1169afbe90
11 changed files with 109 additions and 104 deletions
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71
src/operations.cc
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@@ -29,67 +29,32 @@ using vips::VError;
namespace sharp {
/*
Alpha composite src over dst with given gravity.
Assumes alpha channels are already premultiplied and will be unpremultiplied after.
Composite overlayImage over image at given position
Assumes alpha channels are already premultiplied and will be unpremultiplied after
*/
VImage Composite(VImage src, VImage dst, const int gravity) {
if (IsInputValidForComposition(src, dst)) {
// Enlarge overlay src, if required
if (src.width() < dst.width() || src.height() < dst.height()) {
// Calculate the (left, top) coordinates of the output image within the input image, applying the given gravity.
int left;
int top;
std::tie(left, top) = CalculateCrop(dst.width(), dst.height(), src.width(), src.height(), gravity);
// Embed onto transparent background
std::vector<double> background { 0.0, 0.0, 0.0, 0.0 };
src = src.embed(left, top, dst.width(), dst.height(), VImage::option()
VImage Composite(VImage image, VImage overlayImage, int const left, int const top) {
if (HasAlpha(overlayImage)) {
// Alpha composite
if (overlayImage.width() < image.width() || overlayImage.height() < image.height()) {
// Enlarge overlay
std::vector<double> const background { 0.0, 0.0, 0.0, 0.0 };
overlayImage = overlayImage.embed(left, top, image.width(), image.height(), VImage::option()
->set("extend", VIPS_EXTEND_BACKGROUND)
->set("background", background));
}
return CompositeImage(src, dst);
}
// If the input was not valid for composition the return the input image itself
return dst;
}
VImage Composite(VImage src, VImage dst, const int x, const int y) {
if (IsInputValidForComposition(src, dst)) {
// Enlarge overlay src, if required
if (src.width() < dst.width() || src.height() < dst.height()) {
// Calculate the (left, top) coordinates of the output image within the input image, applying the given gravity.
int left;
int top;
std::tie(left, top) = CalculateCrop(dst.width(), dst.height(), src.width(), src.height(), x, y);
// Embed onto transparent background
std::vector<double> background { 0.0, 0.0, 0.0, 0.0 };
src = src.embed(left, top, dst.width(), dst.height(), VImage::option()
->set("extend", VIPS_EXTEND_BACKGROUND)
->set("background", background));
return AlphaComposite(image, overlayImage);
} else {
if (HasAlpha(image)) {
// Add alpha channel to overlayImage so channels match
double const multiplier = sharp::Is16Bit(overlayImage.interpretation()) ? 256.0 : 1.0;
overlayImage = overlayImage.bandjoin(
VImage::new_matrix(overlayImage.width(), overlayImage.height()).new_from_image(255 * multiplier));
}
return CompositeImage(src, dst);
return image.insert(overlayImage, left, top);
}
// If the input was not valid for composition the return the input image itself
return dst;
}
bool IsInputValidForComposition(VImage src, VImage dst) {
using sharp::CalculateCrop;
using sharp::HasAlpha;
if (!HasAlpha(src)) {
throw VError("Overlay image must have an alpha channel");
}
if (!HasAlpha(dst)) {
throw VError("Image to be overlaid must have an alpha channel");
}
if (src.width() > dst.width() || src.height() > dst.height()) {
throw VError("Overlay image must have same dimensions or smaller");
}
return true;
}
VImage CompositeImage(VImage src, VImage dst) {
VImage AlphaComposite(VImage dst, VImage src) {
// Split src into non-alpha and alpha channels
VImage srcWithoutAlpha = src.extract_band(0, VImage::option()->set("n", src.bands() - 1));
VImage srcAlpha = src[src.bands() - 1] * (1.0 / 255.0);