From cca66b9ec4e494c1d919bff0f71a820d8afab1fa Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 20:24:48 +0200 Subject: Adding upstream version 1.2.2. Signed-off-by: Daniel Baumann --- src/display/grayscale.cpp | 83 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 83 insertions(+) create mode 100644 src/display/grayscale.cpp (limited to 'src/display/grayscale.cpp') diff --git a/src/display/grayscale.cpp b/src/display/grayscale.cpp new file mode 100644 index 0000000..904d238 --- /dev/null +++ b/src/display/grayscale.cpp @@ -0,0 +1,83 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/** \file + * Provide methods to calculate grayscale values (e.g. convert rgba value to grayscale rgba value) + */ + +/* + * Author: + * Johan Engelen + * + * Copyright (C) 2011 Author + * + * Released under GNU GPL v2+, read the file 'COPYING' for more information. + */ + +#include "display/grayscale.h" +#include "color.h" + +namespace Grayscale { + +/* Original values from Johan: +const float red_factor = 0.3; +const float green_factor = 0.59; +const float blue_factor = 0.11; +*/ + +// Values below are from the SVG specification +const float red_factor = 0.2125; +const float green_factor = 0.7154; +const float blue_factor = 0.0721; + +guint32 process(guint32 rgba) { + return process(SP_RGBA32_R_U(rgba), SP_RGBA32_G_U(rgba), SP_RGBA32_B_U(rgba), SP_RGBA32_A_U(rgba)); +} + +guint32 process(unsigned char r, unsigned char g, unsigned char b, unsigned char a) { + + /** To reduce banding in gradients, this calculation is tweaked a bit + * by outputting blue+1 or red+1 or both. The luminance is calculated + * times 4. Then last two bits are used to determine if red and/or blue + * can be increased by one. Then these two bits are discarded. + * So the output color it still looks gray, but has more than 256 steps. + * The assumption is that the eye is most sensitive to green, then red, then blue. + * (hope this trick works :-) Johan) + */ + + guint32 luminance = ( red_factor * (r << 3) + + green_factor * (g << 3) + + blue_factor * (b << 3) ); + unsigned blue_plus_one = (luminance & 0x01) ? 1 : 0; + unsigned red_plus_one = (luminance & 0x02) ? 1 : 0; + unsigned green_plus_one = (luminance & 0x04) ? 1 : 0; + luminance = luminance >> 3; + + if (luminance >= 0xff) { + return SP_RGBA32_U_COMPOSE(0xff, 0xff, 0xff, a); + } else { + return SP_RGBA32_U_COMPOSE(luminance + red_plus_one, luminance + green_plus_one, luminance + blue_plus_one, a); + } +} + +unsigned char luminance(unsigned char r, unsigned char g, unsigned char b) { + guint32 luminance = ( red_factor * r + + green_factor * g + + blue_factor * b ); + if (luminance > 0xff) { + luminance = 0xff; + } + + return luminance & 0xff; +} + +}; + +/* + Local Variables: + mode:c++ + c-file-style:"stroustrup" + c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +)) + indent-tabs-mode:nil + fill-column:99 + End: +*/ +// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:fileencoding=utf-8:textwidth=99 : -- cgit v1.2.3