201 lines
7.4 KiB
C++
201 lines
7.4 KiB
C++
/*
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Support function for Floyd-Steinberg dithering of an 8bit grey-scale BMP image
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on a Monochrome display:
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https://en.wikipedia.org/wiki/Floyd%E2%80%93Steinberg_dithering
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Bitmap format:
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https://en.wikipedia.org/wiki/BMP_file_format
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Example for https://github.com/Bodmer/TFT_eSPI
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The MIT License (MIT)
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Copyright (c) 2015 by Bodmer
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in all
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copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYBR_DATUM HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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SOFTWARE.
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Note: drawFSBmp() is a simplified function and does not handle all possible
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BMP file header variants. It works OK with 8 bit per pixel grey-scale images
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generated by MS Paint and IrfanView.
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*/
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// https://github.com/Bodmer/TFT_eSPI
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//====================================================================================
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// Draw an 8 bit grey-scale bitmap (*.BMP) on a Monochrome display using dithering
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//====================================================================================
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// Uses RAM for buffers (3 * width + 4) ( 532 bytes for 176 pixels)
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// Image must be stored in ESP8266 or ESP32 SPIFFS
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// Quantisation error distribution for pixel X
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// (This is for bottum up drawing of the BMP)
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// |-------|-------|-------|
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// | +3/16 | +5/16 | +1/16 |
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// |-------|-------|-------|
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// | | X | +7/16 |
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// |-------|-------|-------|
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//
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void drawFSBmp(const char *filename, int16_t x, int16_t y) {
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if ((x >= frame.width()) || (y >= frame.height())) return;
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fs::File bmpFS;
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// Open requested file
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bmpFS = SPIFFS.open( filename, "r");
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if (!bmpFS)
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{
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Serial.print("File not found");
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return;
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}
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uint32_t seekOffset, dib_size;
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uint16_t w, h, row, col, num_colors;
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uint8_t r, g, b;
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if (read16(bmpFS) == 0x4D42) // Check it is a valid bitmap header
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{
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read32(bmpFS);
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read32(bmpFS);
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seekOffset = read32(bmpFS); // Pointer to image start
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dib_size = read32(bmpFS); // DIB header size, typically 40 bytes
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w = read32(bmpFS); // Get width and height of image
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h = read32(bmpFS);
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// Check it is 1 plane and 8 bits per pixel and no compression
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if ((read16(bmpFS) == 1) && (read16(bmpFS) == 8) && (read32(bmpFS) == 0))
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{
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read32(bmpFS); // Throw away image size
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read32(bmpFS); // Throw away x pixels per meter
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read32(bmpFS); // Throw away y pixels per meter
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num_colors = read32(bmpFS); // Number of colours in colour table (usually 256)
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uint8_t pixel_color[num_colors]; // Lookup table for grey-scale
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bmpFS.seek(14 + dib_size); // Seek to start of colour table
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// Capture the colour lookup table
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for (uint16_t i = 0; i < num_colors; i++)
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{
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uint32_t abgr = read32(bmpFS); // Assume 4 byte, RGB colours in LS 3 bytes
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pixel_color[i] = (uint8_t) abgr; // For grey-scale R, G, B are same value
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}
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bmpFS.seek(seekOffset); // Seek to start of image
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uint16_t padding = (4 - (w & 3)) & 3; // Calculate the BMP line padding
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// Create an zero an 8 bit pixel line buffer
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uint8_t* lineBuffer = ( uint8_t*) calloc(w , sizeof(uint8_t));
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// Create a 16 bit signed line buffer for the quantisation error
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// Diffusion spreads to x-1 and x+1 so w + 2 avoids a bounds check
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int16_t* qerrBuffer = ( int16_t*) calloc((w + 2)<<1, sizeof(uint8_t));
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y += h - 1; // Start from bottom (assumes bottum up!)
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// Draw row by row from bottom up
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for (row = 0; row < h; row++) {
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// Read a row of pixels
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bmpFS.read(lineBuffer, w);
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// Prep variables
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uint16_t dx = 0;
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uint8_t* bptr = lineBuffer;
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int16_t* qptr = qerrBuffer + 1; // + 1 because diffusion spreads to x-1
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// Lookup color, add quantisation error, clip and clear error buffer
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while(dx < w)
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{
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int16_t depixel = pixel_color[(uint8_t)*bptr] + *qptr;
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if (depixel >255) depixel = 255; // Clip pixel to 0-255
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else if (depixel < 0) depixel = 0;
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*bptr++ = (uint8_t) depixel; // Save new value, inc pointer
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*qptr++ = 0; // Zero error, inc pointer
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dx++; // Next pixel
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}
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dx = 0; // Reset varaibles to start of line
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bptr = lineBuffer;
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qptr = qerrBuffer + 1;
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int32_t qerr = 0;
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int32_t qerr16 = 0;
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// Push the pixel row to screen
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while(dx < w)
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{
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// Add 7/16 of error (error = 0 on first entry)
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int16_t pixel = *bptr + (qerr>>1) - qerr16;
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// Do not clip here so quantisation error accumulates correctly?
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// Draw pixel (black or white) and determine new error
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if (pixel < 128) { frame.drawPixel(x + dx, y, INK); qerr = pixel; }
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else qerr = pixel - 255;
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// Diffuse into error buffer for next pixel line
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qerr16 = qerr>>4; // 1/16 of error
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*(qptr - 1) += (qerr>>2) - qerr16; // Add 3/16 of error
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*(qptr ) += (qerr>>2) + qerr16; // Add 5/16 of error
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*(qptr + 1) += qerr16; // Add 1/16 of error
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bptr++; // Move along pixel and error buffers
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qptr++;
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dx++; // Move coordinate along
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}
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y--;
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// Read any line padding (saves a slow seek)
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if (padding) bmpFS.read(lineBuffer, padding);
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}
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free(lineBuffer);
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free(qerrBuffer);
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}
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else Serial.println("BMP format not recognized.");
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}
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bmpFS.close();
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}
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//====================================================================================
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// Read a 16 bit value from the filing system
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//====================================================================================
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uint16_t read16(fs::File &f) {
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uint16_t result;
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((uint8_t *)&result)[0] = f.read(); // LSB
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((uint8_t *)&result)[1] = f.read(); // MSB
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return result;
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}
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//====================================================================================
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// Read a 32 bit value from the filing system
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//====================================================================================
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uint32_t read32(fs::File &f) {
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uint32_t result;
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((uint8_t *)&result)[0] = f.read(); // LSB
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((uint8_t *)&result)[1] = f.read();
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((uint8_t *)&result)[2] = f.read();
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((uint8_t *)&result)[3] = f.read(); // MSB
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return result;
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}
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// TODO: Add support for colour images by converting RGB to grey-scale
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// grey = (R+G+B)/3
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