BMP to GLCD Bitmap Converter: Tools and Tips for Embedded Displays

What “BMP to GLCD bitmap” means

GLCDs (graphic LCDs) typically require monochrome or specific byte-packed bitmap formats where each byte represents 8 vertical or horizontal pixels, depends on controller (e.g., KS0108, ST7920, SSD1306). Converting a standard BMP (bitmap image file) involves resizing, color reduction, dithering, and packing bits into the target memory/byte order.

Common tools

• ImageMagick (command-line): convert, resize, threshold, and export raw bitmaps.
• GIMP: edit, convert to indexed/greyscale, export raw or as C arrays with plugins.
• LCD Image Converter (Windows): GUI tool that outputs C arrays for many controllers and supports fonts.
• bmp2glcd / bmp2c / custom scripts: small utilities (C, Python) that map BMP pixels into byte-packed arrays.
• Python libraries: Pillow for reading BMPs + custom packing scripts to produce .c/.h arrays.
• Platform-specific plugins: IDE extensions for embedded frameworks (Arduino libraries often include converters).

Steps for reliable conversion

1. Target specs: identify display resolution, color depth (monochrome/greyscale), and controller byte order (vertical vs horizontal bit orientation).
2. Resize/Crop: scale the BMP to the display resolution; preserve aspect with padding if needed.
3. Color reduction: convert to 1-bit (threshold) or desired palette; apply dithering (Floyd–Steinberg) if needed for better perceived detail.
4. Pixel packing: arrange bits per controller convention (e.g., each byte = 8 vertical pixels for SSD1306; some expect rows of 8 horizontal pixels).
5. Byte order and endianness: ensure correct scan order (left-to-right, top-to-bottom) and bit significance (LSB vs MSB first).
6. Output format: generate C arrays, hex dumps, or raw binary matching the target toolchain.

Useful command examples

• Resize and threshold with ImageMagick:

Code
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magick input.bmp -resize 128x64! -colorspace Gray -threshold 50% output.bmp 

• Extract pixels with Python (Pillow) and pack vertical bytes (example outline):

Code
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from PIL import Image im = Image.open(‘output.bmp’).convert(‘1’)

 
pack bits per 8 vertical pixels into bytes for SSD1306-style displays…
 

Tips and pitfalls

• Verify controller convention: using the wrong packing (vertical vs horizontal) yields transposed or garbled images.
• Test with simple patterns first (checkerboard, single pixel) to confirm byte/bit ordering.
• Use dithering for photos; for icons, use manual touch-up to improve legibility.
• Remember page addressing: displays with page-based RAM need data sent per page (usually 8 rows).
• When memory is tight, compress bitmaps (RLE) or store in PROGMEM/flash rather than RAM.
• Watch for BMP header differences (BMP versions) if writing custom readers.

Quick checklist before flashing

• Resolution matches display.
• Monochrome conversion and dithering acceptable.
• Bit/byte packing matches controller.
• Data stored in correct memory section (flash vs RAM).
• Test small images first.

If you want, I can generate a ready-to-use Python script that converts a BMP into a C array for a specific controller (tell me controller and resolution).