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Prevent aliasing by using dynamic values for shrink(-on-load)

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Lovell Fuller
2017-05-13 18:46:39 +01:00
parent 48f69f3d88
commit e398b471e1
6 changed files with 18 additions and 1 deletions
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13
src/pipeline.cc
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@@ -242,6 +242,12 @@ class PipelineWorker : public Nan::AsyncWorker {
shrink_on_load = 2;
}
}
// Help ensure a final kernel-based reduction to prevent shrink aliasing
if (shrink_on_load > 1 && (xresidual == 1.0 || yresidual == 1.0)) {
shrink_on_load = shrink_on_load / 2;
xfactor = xfactor * 2;
yfactor = yfactor * 2;
}
if (shrink_on_load > 1) {
// Reload input using shrink-on-load
vips::VOption *option = VImage::option()->set("shrink", shrink_on_load);
@@ -285,6 +291,13 @@ class PipelineWorker : public Nan::AsyncWorker {
std::swap(xresidual, yresidual);
}
}
// Help ensure a final kernel-based reduction to prevent shrink aliasing
if ((xshrink > 1 || yshrink > 1) && (xresidual == 1.0 || yresidual == 1.0)) {
xshrink = xshrink / 2;
yshrink = yshrink / 2;
xresidual = xresidual / 2.0;
yresidual = yresidual / 2.0;
}
// Ensure we're using a device-independent colour space
if (sharp::HasProfile(image)) {