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Refactor internal 'resize' to more apt 'pipeline'
Refactor 'composite' C to C++ 'operations'
This commit is contained in:
Lovell Fuller
191
src/operations.cc
Executable file
191
src/operations.cc
Executable file
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#include <vips/vips.h>
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#include "operations.h"
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namespace sharp {
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/*
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Composite images `src` and `dst` with premultiplied alpha channel and output
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image with premultiplied alpha.
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*/
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int Composite(VipsObject *context, VipsImage *srcPremultiplied, VipsImage *dstPremultiplied, VipsImage **outPremultiplied) {
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if (srcPremultiplied->Bands != 4 || dstPremultiplied->Bands != 4)
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return -1;
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// Extract RGB bands:
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VipsImage *srcRGBPremultiplied;
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if (vips_extract_band(srcPremultiplied, &srcRGBPremultiplied, 0, "n", srcPremultiplied->Bands - 1, NULL))
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return -1;
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vips_object_local(context, srcRGBPremultiplied);
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VipsImage *dstRGBPremultiplied;
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if (vips_extract_band(dstPremultiplied, &dstRGBPremultiplied, 0, "n", dstPremultiplied->Bands - 1, NULL))
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return -1;
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vips_object_local(context, dstRGBPremultiplied);
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// Extract alpha bands:
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VipsImage *srcAlpha;
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if (vips_extract_band(srcPremultiplied, &srcAlpha, srcPremultiplied->Bands - 1, "n", 1, NULL))
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return -1;
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vips_object_local(context, srcAlpha);
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VipsImage *dstAlpha;
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if (vips_extract_band(dstPremultiplied, &dstAlpha, dstPremultiplied->Bands - 1, "n", 1, NULL))
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return -1;
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vips_object_local(context, dstAlpha);
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// Compute normalized input alpha channels:
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VipsImage *srcAlphaNormalized;
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if (vips_linear1(srcAlpha, &srcAlphaNormalized, 1.0 / 255.0, 0.0, NULL))
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return -1;
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vips_object_local(context, srcAlphaNormalized);
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VipsImage *dstAlphaNormalized;
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if (vips_linear1(dstAlpha, &dstAlphaNormalized, 1.0 / 255.0, 0.0, NULL))
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return -1;
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vips_object_local(context, dstAlphaNormalized);
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//
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// Compute normalized output alpha channel:
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//
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// References:
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// - http://en.wikipedia.org/wiki/Alpha_compositing#Alpha_blending
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// - https://github.com/jcupitt/ruby-vips/issues/28#issuecomment-9014826
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//
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// out_a = src_a + dst_a * (1 - src_a)
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// ^^^^^^^^^^^
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// t0
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// ^^^^^^^^^^^^^^^^^^^
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// t1
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VipsImage *t0;
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if (vips_linear1(srcAlphaNormalized, &t0, -1.0, 1.0, NULL))
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return -1;
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vips_object_local(context, t0);
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VipsImage *t1;
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if (vips_multiply(dstAlphaNormalized, t0, &t1, NULL))
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return -1;
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vips_object_local(context, t1);
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VipsImage *outAlphaNormalized;
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if (vips_add(srcAlphaNormalized, t1, &outAlphaNormalized, NULL))
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return -1;
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vips_object_local(context, outAlphaNormalized);
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//
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// Compute output RGB channels:
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//
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// Wikipedia:
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// out_rgb = (src_rgb * src_a + dst_rgb * dst_a * (1 - src_a)) / out_a
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// ^^^^^^^^^^^
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// t0
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//
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// Omit division by `out_a` since `Compose` is supposed to output a
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// premultiplied RGBA image as reversal of premultiplication is handled
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// externally.
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//
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VipsImage *t2;
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if (vips_multiply(dstRGBPremultiplied, t0, &t2, NULL))
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return -1;
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vips_object_local(context, t2);
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VipsImage *outRGBPremultiplied;
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if (vips_add(srcRGBPremultiplied, t2, &outRGBPremultiplied, NULL))
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return -1;
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vips_object_local(context, outRGBPremultiplied);
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// Denormalize output alpha channel:
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VipsImage *outAlpha;
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if (vips_linear1(outAlphaNormalized, &outAlpha, 255.0, 0.0, NULL))
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return -1;
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vips_object_local(context, outAlpha);
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// Combine RGB and alpha channel into output image:
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VipsImage *joined;
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if (vips_bandjoin2(outRGBPremultiplied, outAlpha, &joined, NULL))
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return -1;
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// Return a reference to the composited output image
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*outPremultiplied = joined;
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return 0;
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}
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/*
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* Premultiply alpha channel of `image`.
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*/
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int Premultiply(VipsObject *context, VipsImage *image, VipsImage **out) {
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VipsImage *imagePremultiplied;
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#if (VIPS_MAJOR_VERSION >= 9 || (VIPS_MAJOR_VERSION >= 8 && VIPS_MINOR_VERSION >= 1))
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if (vips_premultiply(image, &imagePremultiplied, NULL))
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return -1;
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#else
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VipsImage *imageRGB;
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if (vips_extract_band(image, &imageRGB, 0, "n", image->Bands - 1, NULL))
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return -1;
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vips_object_local(context, imageRGB);
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VipsImage *imageAlpha;
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if (vips_extract_band(image, &imageAlpha, image->Bands - 1, "n", 1, NULL))
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return -1;
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vips_object_local(context, imageAlpha);
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VipsImage *imageAlphaNormalized;
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if (vips_linear1(imageAlpha, &imageAlphaNormalized, 1.0 / 255.0, 0.0, NULL))
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return -1;
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vips_object_local(context, imageAlphaNormalized);
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VipsImage *imageRGBPremultiplied;
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if (vips_multiply(imageRGB, imageAlphaNormalized, &imageRGBPremultiplied, NULL))
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return -1;
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vips_object_local(context, imageRGBPremultiplied);
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if (vips_bandjoin2(imageRGBPremultiplied, imageAlpha, &imagePremultiplied, NULL))
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return -1;
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#endif
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// Return a reference to the premultiplied output image
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*out = imagePremultiplied;
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return 0;
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}
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/*
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* Unpremultiply alpha channel of `image`.
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*/
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int Unpremultiply(VipsObject *context, VipsImage *image, VipsImage **out) {
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VipsImage *imageUnpremultiplied;
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#if (VIPS_MAJOR_VERSION >= 9 || (VIPS_MAJOR_VERSION >= 8 && VIPS_MINOR_VERSION >= 1))
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if (vips_unpremultiply(image, &imageUnpremultiplied, NULL))
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return -1;
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#else
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VipsImage *imageRGBPremultipliedTransformed;
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if (vips_extract_band(image, &imageRGBPremultipliedTransformed, 0, "n", image->Bands - 1, NULL))
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return -1;
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vips_object_local(context, imageRGBPremultipliedTransformed);
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VipsImage *imageAlphaTransformed;
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if (vips_extract_band(image, &imageAlphaTransformed, image->Bands - 1, "n", 1, NULL))
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return -1;
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vips_object_local(context, imageAlphaTransformed);
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VipsImage *imageAlphaNormalizedTransformed;
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if (vips_linear1(imageAlphaTransformed, &imageAlphaNormalizedTransformed, 1.0 / 255.0, 0.0, NULL))
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return -1;
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vips_object_local(context, imageAlphaNormalizedTransformed);
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VipsImage *imageRGBUnpremultipliedTransformed;
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if (vips_divide(imageRGBPremultipliedTransformed, imageAlphaNormalizedTransformed, &imageRGBUnpremultipliedTransformed, NULL))
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return -1;
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vips_object_local(context, imageRGBUnpremultipliedTransformed);
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if (vips_bandjoin2(imageRGBUnpremultipliedTransformed, imageAlphaTransformed, &imageUnpremultiplied, NULL))
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return -1;
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#endif
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// Return a reference to the unpremultiplied output image
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*out = imageUnpremultiplied;
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return 0;
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}
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} // namespace sharp
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