f96b6ab29c
## Summary * **What is the goal of this PR?** Replace simple threshold-based grayscale quantization with ordered dithering using a 4x4 Bayer matrix. This eliminates color banding artifacts and produces smoother gradients on e-ink display. * **What changes are included?** - Add 4x4 Bayer dithering matrix for 16-level threshold patterns - Modify `grayscaleTo2Bit()` function to accept pixel coordinates and apply position-based dithering - Replace simple `grayscale >> 6` threshold with ordered dithering algorithm that produces smoother gradients ## Additional Context * Bayer matrix approach: The 4x4 Bayer matrix creates a repeating pattern that distributes quantization error spatially, effectively simulating 16 levels of gray using only 4 actual color levels (black, dark gray, light gray, white). * Cache invalidation: Existing cached `cover.bmp` files will need to be deleted to see the improved rendering, as the converter only runs when the cache is missing.
60 lines
1.3 KiB
C++
60 lines
1.3 KiB
C++
#pragma once
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#include <FS.h>
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enum class BmpReaderError : uint8_t {
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Ok = 0,
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FileInvalid,
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SeekStartFailed,
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NotBMP,
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DIBTooSmall,
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BadPlanes,
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UnsupportedBpp,
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UnsupportedCompression,
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BadDimensions,
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ImageTooLarge,
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PaletteTooLarge,
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SeekPixelDataFailed,
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BufferTooSmall,
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OomRowBuffer,
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ShortReadRow,
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};
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class Bitmap {
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public:
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static const char* errorToString(BmpReaderError err);
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explicit Bitmap(File& file) : file(file) {}
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~Bitmap();
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BmpReaderError parseHeaders();
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BmpReaderError readRow(uint8_t* data, uint8_t* rowBuffer, int rowY) const;
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BmpReaderError rewindToData() const;
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int getWidth() const { return width; }
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int getHeight() const { return height; }
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bool isTopDown() const { return topDown; }
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bool hasGreyscale() const { return bpp > 1; }
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int getRowBytes() const { return rowBytes; }
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private:
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static uint16_t readLE16(File& f);
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static uint32_t readLE32(File& f);
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File& file;
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int width = 0;
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int height = 0;
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bool topDown = false;
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uint32_t bfOffBits = 0;
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uint16_t bpp = 0;
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int rowBytes = 0;
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uint8_t paletteLum[256] = {};
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// Floyd-Steinberg dithering state (mutable for const methods)
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mutable int16_t* errorCurRow = nullptr;
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mutable int16_t* errorNextRow = nullptr;
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mutable int lastRowY = -1; // Track row progression for error propagation
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};
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