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Port ImageMagick's OrderedDither algorithm, and use that instead of
ImageOps' quantize to dither images to the eInk palette. It works much better for our intended purpose, and it's pretty fast.
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@@ -3,7 +3,7 @@ | |
| from __future__ import absolute_import, division, print_function, unicode_literals | ||
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| __license__ = 'GPL v3' | ||
| __copyright__ = '2010-2018, Timothy Legge <[email protected]>, Kovid Goyal <[email protected]> and David Forrester <[email protected]>' | ||
| __copyright__ = '2010-2019, Timothy Legge <[email protected]>, Kovid Goyal <[email protected]> and David Forrester <[email protected]>' | ||
| __docformat__ = 'restructuredtext en' | ||
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| ''' | ||
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@@ -2651,7 +2651,8 @@ def _calculate_kobo_cover_size(self, library_size, kobo_size, expand, keep_cover | |
| # NOTE: Loosely based on Qt's QSize::scaled implementation | ||
| if keep_cover_aspect: | ||
| # NOTE: Py3k wouldn't need explicit casts to return a float | ||
| # NOTE: Unlike Qt, we round to avoid accumulating errors | ||
| # NOTE: Unlike Qt, we round to avoid accumulating errors, | ||
| # as ImageOps will then floor via fit_image | ||
| aspect_ratio = library_size[0] / float(library_size[1]) | ||
| rescaled_width = int(round(kobo_size[1] * aspect_ratio)) | ||
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| /* | ||
| * Copyright 1999-2019 ImageMagick Studio LLC | ||
| * | ||
| * Licensed under the ImageMagick License (the "License"); you may not use | ||
| * this file except in compliance with the License. You may obtain a copy | ||
| * of the License at | ||
| * | ||
| * https://imagemagick.org/script/license.php | ||
| * Unless required by applicable law or agreed to in writing, software | ||
| * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT | ||
| * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the | ||
| * License for the specific language governing permissions and limitations | ||
| * under the License. | ||
| */ | ||
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| #include "imageops.h" | ||
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| // Just in case, as I don't want to deal with MSVC madness... | ||
| #if defined _MSC_VER && _MSC_VER < 1700 | ||
| typedef unsigned __int8 uint8_t; | ||
| #define UINT8_MAX _UI8_MAX | ||
| typedef unsigned __int32 uint32_t; | ||
| #else | ||
| #include <cstdint> | ||
| #endif | ||
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| // Quantize an 8-bit color value down to a palette of 16 evenly spaced colors, using an ordered 8x8 dithering pattern. | ||
| // With a grayscale input, this happens to match the eInk palette perfectly ;). | ||
| // If the input is not grayscale, and the output fb is not grayscale either, | ||
| // this usually still happens to match the eInk palette after the EPDC's own quantization pass. | ||
| // c.f., https://en.wikipedia.org/wiki/Ordered_dithering | ||
| // & https://github.com/ImageMagick/ImageMagick/blob/ecfeac404e75f304004f0566557848c53030bad6/MagickCore/threshold.c#L1627 | ||
| // NOTE: As the references imply, this is straight from ImageMagick, | ||
| // with only minor simplifications to enforce Q8 & avoid fp maths. | ||
| static uint8_t | ||
| dither_o8x8(int x, int y, uint8_t v) | ||
| { | ||
| // c.f., https://github.com/ImageMagick/ImageMagick/blob/ecfeac404e75f304004f0566557848c53030bad6/config/thresholds.xml#L107 | ||
| static const uint8_t threshold_map_o8x8[] = { 1, 49, 13, 61, 4, 52, 16, 64, 33, 17, 45, 29, 36, 20, 48, 32, | ||
| 9, 57, 5, 53, 12, 60, 8, 56, 41, 25, 37, 21, 44, 28, 40, 24, | ||
| 3, 51, 15, 63, 2, 50, 14, 62, 35, 19, 47, 31, 34, 18, 46, 30, | ||
| 11, 59, 7, 55, 10, 58, 6, 54, 43, 27, 39, 23, 42, 26, 38, 22 }; | ||
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| // Constants: | ||
| // Quantum = 8; Levels = 16; map Divisor = 65 | ||
| // QuantumRange = 0xFF | ||
| // QuantumScale = 1.0 / QuantumRange | ||
| // | ||
| // threshold = QuantumScale * v * ((L-1) * (D-1) + 1) | ||
| // NOTE: The initial computation of t (specifically, what we pass to DIV255) would overflow an uint8_t. | ||
| // With a Q8 input value, we're at no risk of ever underflowing, so, keep to unsigned maths. | ||
| // Technically, an uint16_t would be wide enough, but it gains us nothing, | ||
| // and requires a few explicit casts to make GCC happy ;). | ||
| uint32_t t = DIV255(v * ((15U << 6) + 1U)); | ||
| // level = t / (D-1); | ||
| uint32_t l = (t >> 6); | ||
| // t -= l * (D-1); | ||
| t = (t - (l << 6)); | ||
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| // map width & height = 8 | ||
| // c = ClampToQuantum((l+(t >= map[(x % mw) + mw * (y % mh)])) * QuantumRange / (L-1)); | ||
| uint32_t q = ((l + (t >= threshold_map_o8x8[(x & 7U) + 8U * (y & 7U)])) * 17); | ||
| // NOTE: We're doing unsigned maths, so, clamping is basically MIN(q, UINT8_MAX) ;). | ||
| // The only overflow we should ever catch should be for a few black (v = 0xFF) input pixels | ||
| // that get shifted to the next step (i.e., q = 272 (0xFF + 17)). | ||
| return (q > UINT8_MAX ? UINT8_MAX : reinterpret_cast<uint8_t>(q); | ||
| } | ||
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| QImage ordered_dither(const QImage &image) { // {{{ | ||
| ScopedGILRelease PyGILRelease; | ||
| QImage img = image; | ||
| QRgb *row = NULL, *pixel = NULL; | ||
| int y = 0, x = 0, width = img.width(), height = img.height(); | ||
| uint8_t gray = 0, dithered = 0; | ||
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| // We're running behind blend_image, so, we should only ever be fed RGB32 as input... | ||
| if (img.format() != QImage::Format_RGB32) { | ||
| img = img.convertToFormat(QImage::Format_RGB32); | ||
| if (img.isNull()) throw std::bad_alloc(); | ||
| } | ||
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| for (y = 0; y < height; y++) { | ||
| row = reinterpret_cast<QRgb*>(img.scanLine(y)); | ||
| for (x = 0, pixel = row; x < width; x++, pixel++) { | ||
| // We're running behind grayscale_image, so R = G = B | ||
| gray = qRed(*pixel); | ||
| dithered = dither_o8x8(x, y, gray); | ||
| *pixel = qRgb(dithered, dithered, dithered); | ||
| } | ||
| } | ||
| return img; | ||
| } // }}} |
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