Simple program for visualizing gamuts

tools/visualize_color_gamut.cpp

+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "Resources.h"
+
+#include "SkBitmap.h"
+#include "SkCanvas.h"
+#include "SkCodec.h"
+#include "SkColorSpace.h"
+#include "SkCommandLineFlags.h"
+#include "SkForceLinking.h"
+#include "SkImageEncoder.h"
+#include "SkMatrix44.h"
+#include "SkOSFile.h"
+
+__SK_FORCE_IMAGE_DECODER_LINKING;
+
+DEFINE_string2(input, i, "input", "A path to the input image.");
+
+/**
+ *  Loads the triangular gamut as a set of three points.
+ */
+static void load_gamut(SkPoint rgb[], const SkMatrix44& xyz) {
+    // rx = rX / (rX + rY + rZ)
+    // ry = rX / (rX + rY + rZ)
+    // gx, gy, bx, and gy are calulcated similarly.
+    float rSum = xyz.get(0, 0) + xyz.get(0, 1) + xyz.get(0, 2);
+    float gSum = xyz.get(1, 0) + xyz.get(1, 1) + xyz.get(1, 2);
+    float bSum = xyz.get(2, 0) + xyz.get(2, 1) + xyz.get(2, 2);
+    rgb[0].fX = xyz.get(0, 0) / rSum;
+    rgb[0].fY = xyz.get(0, 1) / rSum;
+    rgb[1].fX = xyz.get(1, 0) / gSum;
+    rgb[1].fY = xyz.get(1, 1) / gSum;
+    rgb[2].fX = xyz.get(2, 0) / bSum;
+    rgb[2].fY = xyz.get(2, 1) / bSum;
+}
+
+/**
+ *  Calculates the area of the triangular gamut.
+ */
+float calculate_area(SkPoint abc[]) {
+    SkPoint a = abc[0];
+    SkPoint b = abc[1];
+    SkPoint c = abc[2];
+    return 0.5f * SkTAbs(a.fX*b.fY + b.fX*c.fY - a.fX*c.fY - c.fX*b.fY - b.fX*a.fY);
+}
+
+int main(int argc, char** argv) {
+    SkCommandLineFlags::SetUsage(
+            "Usage: visualize_color_gamut -i <path to input input>\n"
+            "Output: Outputs visualization of the color gamut to image_gamut.png\n");

[jcgregorio, 2016/05/13 13:36:36]

Comment doesn't match actual code, currently writes to "out.png".

[msarett, 2016/05/13 14:02:05]

Thanks!  Fixed this to use output filename passed by a flag.

+    SkCommandLineFlags::Parse(argc, argv);
+    const char* image = FLAGS_input[0];
+
+    SkAutoTUnref<SkData> data(SkData::NewFromFileName(image));
+    if (!data) {
+        SkDebugf("Cannot find input image.\n");
+        return -1;
+    }
+    SkAutoTDelete<SkCodec> codec(SkCodec::NewFromData(data));
+    if (!codec) {
+        SkDebugf("Invalid input image.\n");
+        return -1;
+    }
+
+    // Load a graph of the CIE XYZ color gamut.
+    SkBitmap bitmap;
+    if (!GetResourceAsBitmap("gamut.png", &bitmap)) {
+        SkDebugf("Program failure.\n");
+        return -1;
+    }
+    SkCanvas canvas(bitmap);
+
+    sk_sp<SkColorSpace> colorSpace = sk_ref_sp(codec->getColorSpace());
+    if (!colorSpace) {
+        SkDebugf("Image had no embedded color space information.  Defaulting to sRGB.\n");
+        colorSpace = SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named);
+    }
+
+    // Calculate the points in the gamut from the XYZ values.
+    SkMatrix44 xyz = colorSpace->xyz();
+    SkPoint rgb[4];
+    load_gamut(rgb, xyz);
+
+    // Report the XYZ values.
+    SkDebugf("      X    Y    Z\n");
+    SkDebugf("Red   %.2f %.2f %.2f\n", xyz.get(0, 0), xyz.get(0, 1), xyz.get(0, 2));
+    SkDebugf("Green %.2f %.2f %.2f\n", xyz.get(1, 0), xyz.get(1, 1), xyz.get(1, 2));
+    SkDebugf("Blue  %.2f %.2f %.2f\n", xyz.get(2, 0), xyz.get(2, 1), xyz.get(2, 2));
+
+    // Report the area of the gamut.
+    SkDebugf("Area of Gamut: %g\n", calculate_area(rgb));
+
+    // Now transform the points so they can be drawn on our canvas.  We use 1000 pixels
+    // to represent the space from 0 to 1.  Note that the graph is at an offset of (50, 50).
+    // Also note that y increases as we move down the canvas.
+    rgb[0].fX = 50 + 1000*rgb[0].fX;
+    rgb[0].fY = 50 + 1000*(1 - rgb[0].fY);
+    rgb[1].fX = 50 + 1000*rgb[1].fX;
+    rgb[1].fY = 50 + 1000*(1 - rgb[1].fY);
+    rgb[2].fX = 50 + 1000*rgb[2].fX;
+    rgb[2].fY = 50 + 1000*(1 - rgb[2].fY);
+
+    // Repeat the first point to connect the polygon.
+    rgb[3] = rgb[0];
+
+    SkPaint paint;
+    canvas.drawPoints(SkCanvas::kPolygon_PointMode, 4, rgb, paint);
+
+    // Finally, encode the result to out.png.
+    SkAutoTUnref<SkData> out(SkImageEncoder::EncodeData(bitmap, SkImageEncoder::kPNG_Type, 100));
+    if (!out) {
+        SkDebugf("Failed to encode output.\n");
+        return -1;
+    }
+    SkFILEWStream stream("out.png");

[jcgregorio, 2016/05/13 13:36:36]

Can the output filename be made into a flag?

[msarett, 2016/05/13 14:02:05]

Yes! Done.

+    bool result = stream.write(out->data(), out->size());
+    if (!result) {
+        SkDebugf("Failed to write output.\n");
+        return -1;
+    }
+
+    return 0;
+}