#include #include "common.h" #include "operations.h" using vips::VImage; namespace sharp { /* Alpha composite src over dst Assumes alpha channels are already premultiplied and will be unpremultiplied after */ VImage Composite(VImage src, VImage dst) { using sharp::HasAlpha; // Split src into non-alpha and alpha VImage srcWithoutAlpha = src.extract_band(0, VImage::option()->set("n", src.bands() - 1)); VImage srcAlpha = src[src.bands() - 1] * (1.0 / 255.0); // Split dst into non-alpha and alpha channels VImage dstWithoutAlpha; VImage dstAlpha; if (HasAlpha(dst)) { // Non-alpha: extract all-but-last channel dstWithoutAlpha = dst.extract_band(0, VImage::option()->set("n", dst.bands() - 1)); // Alpha: Extract last channel dstAlpha = dst[dst.bands() - 1] * (1.0 / 255.0); } else { // Non-alpha: Copy reference dstWithoutAlpha = dst; // Alpha: Use blank, opaque (0xFF) image dstAlpha = VImage::black(dst.width(), dst.height()).invert(); } // // Compute normalized output alpha channel: // // References: // - http://en.wikipedia.org/wiki/Alpha_compositing#Alpha_blending // - https://github.com/jcupitt/ruby-vips/issues/28#issuecomment-9014826 // // out_a = src_a + dst_a * (1 - src_a) // ^^^^^^^^^^^ // t0 VImage t0 = srcAlpha.linear(-1.0, 1.0); VImage outAlphaNormalized = srcAlpha + dstAlpha * t0; // // Compute output RGB channels: // // Wikipedia: // out_rgb = (src_rgb * src_a + dst_rgb * dst_a * (1 - src_a)) / out_a // ^^^^^^^^^^^ // t0 // // Omit division by `out_a` since `Compose` is supposed to output a // premultiplied RGBA image as reversal of premultiplication is handled // externally. // VImage outRGBPremultiplied = srcWithoutAlpha + dstWithoutAlpha * t0; // Combine RGB and alpha channel into output image: return outRGBPremultiplied.bandjoin(outAlphaNormalized * 255.0); } /* * Stretch luminance to cover full dynamic range. */ VImage Normalize(VImage image) { // Get original colourspace VipsInterpretation typeBeforeNormalize = image.interpretation(); if (typeBeforeNormalize == VIPS_INTERPRETATION_RGB) { typeBeforeNormalize = VIPS_INTERPRETATION_sRGB; } // Convert to LAB colourspace VImage lab = image.colourspace(VIPS_INTERPRETATION_LAB); // Extract luminance VImage luminance = lab[0]; // Find luminance range VImage stats = luminance.stats(); double min = stats(0, 0)[0]; double max = stats(1, 0)[0]; if (min != max) { // Extract chroma VImage chroma = lab.extract_band(1, VImage::option()->set("n", 2)); // Calculate multiplication factor and addition double f = 100.0 / (max - min); double a = -(min * f); // Scale luminance, join to chroma, convert back to original colourspace VImage normalized = luminance.linear(f, a).bandjoin(chroma).colourspace(typeBeforeNormalize); // Attach original alpha channel, if any if (HasAlpha(image)) { // Extract original alpha channel VImage alpha = image[image.bands() - 1]; // Join alpha channel to normalised image return normalized.bandjoin(alpha); } else { return normalized; } } return image; } /* * Gamma encoding/decoding */ VImage Gamma(VImage image, double const exponent) { if (HasAlpha(image)) { // Separate alpha channel VImage imageWithoutAlpha = image.extract_band(0, VImage::option()->set("n", image.bands() - 1)); VImage alpha = image[image.bands() - 1]; return imageWithoutAlpha.gamma(VImage::option()->set("exponent", exponent)).bandjoin(alpha); } else { return image.gamma(VImage::option()->set("exponent", exponent)); } } /* * Gaussian blur (use sigma <0 for fast blur) */ VImage Blur(VImage image, double const sigma) { if (sigma < 0.0) { // Fast, mild blur - averages neighbouring pixels VImage blur = VImage::new_matrixv(3, 3, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0); blur.set("scale", 9.0); return image.conv(blur); } else { // Slower, accurate Gaussian blur return image.gaussblur(sigma); } } /* * Sharpen flat and jagged areas. Use radius of -1 for fast sharpen. */ VImage Sharpen(VImage image, int const radius, double const flat, double const jagged) { if (radius == -1) { // Fast, mild sharpen VImage sharpen = VImage::new_matrixv(3, 3, -1.0, -1.0, -1.0, -1.0, 32.0, -1.0, -1.0, -1.0, -1.0); sharpen.set("scale", 24.0); return image.conv(sharpen); } else { // Slow, accurate sharpen in LAB colour space, with control over flat vs jagged areas return image.sharpen( VImage::option()->set("radius", radius)->set("m1", flat)->set("m2", jagged) ); } } } // namespace sharp