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Add support for clipping/cutting out (#435) (#448)

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USAGE: overlayWith('overlayimage.png', { cutout: true } )
This commit is contained in:
Kleis Auke Wolthuizen
2016-06-25 17:48:01 +02:00
committed by Lovell Fuller
parent f1ead06645
commit 2e9cd83ed2
21 changed files with 167 additions and 10 deletions
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59
src/operations.cc
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@@ -81,6 +81,65 @@ namespace sharp {
return outRGBPremultiplied.bandjoin(outAlphaNormalized * 255.0);
}
/*
Cutout src over dst with given gravity.
*/
VImage Cutout(VImage mask, VImage dst, const int gravity) {
using sharp::CalculateCrop;
using sharp::HasAlpha;
using sharp::MaximumImageAlpha;
bool maskHasAlpha = HasAlpha(mask);
if (!maskHasAlpha && mask.bands() > 1) {
throw VError("Overlay image must have an alpha channel or one band");
}
if (!HasAlpha(dst)) {
throw VError("Image to be overlaid must have an alpha channel");
}
if (mask.width() > dst.width() || mask.height() > dst.height()) {
throw VError("Overlay image must have same dimensions or smaller");
}
// Enlarge overlay mask, if required
if (mask.width() < dst.width() || mask.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(), mask.width(), mask.height(), gravity);
// Embed onto transparent background
std::vector<double> background { 0.0, 0.0, 0.0, 0.0 };
mask = mask.embed(left, top, dst.width(), dst.height(), VImage::option()
->set("extend", VIPS_EXTEND_BACKGROUND)
->set("background", background)
);
}
// we use the mask alpha if it has alpha
if(maskHasAlpha) {
mask = mask.extract_band(mask.bands() - 1, VImage::option()->set("n", 1));;
}
// Split dst into an optional alpha
VImage dstAlpha = dst.extract_band(dst.bands() - 1, VImage::option()->set("n", 1));
// we use the dst non-alpha
dst = dst.extract_band(0, VImage::option()->set("n", dst.bands() - 1));
// the range of the mask and the image need to match .. one could be
// 16-bit, one 8-bit
int dstMax = MaximumImageAlpha(dst.interpretation());
int maskMax = MaximumImageAlpha(mask.interpretation());
// combine the new mask and the existing alpha ... there are
// many ways of doing this, mult is the simplest
mask = dstMax * ((mask / maskMax) * (dstAlpha / dstMax));
// append the mask to the image data ... the mask might be float now,
// we must cast the format down to match the image data
return dst.bandjoin(mask.cast(dst.format()));
}
/*
* Stretch luminance to cover full dynamic range.
*/