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.bmp

BMP test images

Uncompressed bitmaps with exactly the header variant you need: classic 24-bit, 32-bit with an alpha mask, 8-bit palette, and top-down rows.

Open the .bmp generator

Or start from a preset

What is a BMP image?

Short answer

BMP is the Windows bitmap format: a file header, a DIB header (BITMAPINFOHEADER or a later version), an optional palette, then pixel rows padded to 4 bytes, usually stored from the bottom row up.

Readers often assume 24-bit, bottom-up rows. A negative height (top-down), a BITMAPV4 header with bit masks, or a palette image catches those assumptions.

Anatomy of a BMP image

  • BMSignature, file size and pixel data offset
  • BITMAPINFOHEADER40 bytes: size, bit depth, compression
  • BITMAPV4HEADER108 bytes: adds RGBA bit masks
  • palette256 entries for 8-bit images
  • rowsBGR(A), padded to 4 bytes, bottom-up unless height is negative

What you can generate

  • 24-bit BGR
  • 32-bit BGRA with a BITMAPV4 alpha mask
  • 8-bit grayscale palette
  • Top-down rows (negative height)
  • Odd widths that need row padding

How to make one

  1. Open the BMP image generator, or start from a preset above.
  2. Set the size and switch on the edge cases you need; the preview and size estimate follow every change.
  3. Generate, then download. The file is made in your browser, and the same preset and seed always give you the same file.

Questions

Yes. BMP is uncompressed, so the size shown in step 2 is the exact size of the file.

The classic 40-byte header has no alpha mask, so many readers ignore the fourth byte. BITMAPV4 declares it.

Related formats