BmpToRaw: Quick Guide to Converting BMP Images to RAW

Optimizing Image Quality with BmpToRaw SettingsConverting BMP images to RAW format can be straightforward, but maintaining or improving image quality during conversion requires careful attention to settings, workflow, and the characteristics of both formats. This article explains how to get the best results when using BmpToRaw: what each setting does, trade-offs to consider, recommended workflows, and practical tips for different use cases (photography, computer vision, printing, embedded systems).

What BmpToRaw does and when to use it

BmpToRaw is a conversion tool (CLI or library) that reads BMP (Bitmap) files — which store pixel data, color depth, and optional metadata — and outputs RAW images, typically a byte-for-byte representation of pixel values without headers or compression. RAW outputs are commonly used in embedded systems, custom graphics pipelines, and machine-vision applications where minimal overhead and predictable memory layout matter.

Use BmpToRaw when you need:

Fast, predictable pixel arrays for low-level processing.
Storage for pixel data with no file-format parsing overhead.
Inputs for devices or APIs that expect plain pixel buffers.

Key concepts that affect image quality

Bit depth and color channels: BMP supports 1, 4, 8, 16, 24, and 32 bpp variants. RAW must match or intentionally change bit depth (e.g., 24 bpp BMP -> 16 bpp RAW). Downsampling bit depth loses color fidelity.
Color space and gamma: BMP typically stores pixels in sRGB or device-dependent space. RAW has no embedded color profile; interpreting software must assume or be told the color space.
Endianness and byte order: Especially for ⁄₃₂-bit per channel data, ensure the byte order matches the target system.
Row padding and stride: BMP rows are often aligned to 4-byte boundaries. RAW usually expects tightly packed rows unless specified otherwise.
Alpha channel handling: 32 bpp BMP may include alpha; decide whether to preserve, premultiply, or discard it.
Dithering and quantization: When reducing bit depth, controlled dithering can reduce banding.

Important BmpToRaw settings and how they affect quality

Bit depth conversion

Setting: target bit depth (e.g., 8, 16, 24, 32 bpp)
Effect: Converting to a lower bit depth reduces color precision and dynamic range.
Recommendation: Keep the same bit depth when possible. If reducing, use dithering (see below).

Channel order / Pixel format

Setting: RGB, BGR, RGBA, BGRA, grayscale
Effect: Incorrect channel order causes swapped colors; mismatched alpha handling can produce transparency artifacts.
Recommendation: Match your downstream consumer’s expected order. For interoperability, use RGB for RGB images and explicitly state byte order for multibyte channels.

Byte order (endianness)

Setting: little-endian vs big-endian for multi-byte channels
Effect: Wrong endianness produces scrambled color values.
Recommendation: Use little-endian on most modern platforms (x86), but confirm for embedded/ARM targets.

Row alignment / stride

Setting: pad rows to 4 bytes (BMP default) or use tight packing
Effect: Extra padding can lead to misinterpreted pixels if downstream expects no padding.
Recommendation: Prefer tightly packed rows (no padding) unless the target requires alignment.

Color space tag

Setting: specify sRGB, linear, or none
Effect: Without a color space tag, downstream may assume wrong gamma causing washed-out or overly contrasty images.
Recommendation: Explicitly label RAW data as sRGB if converting from standard BMPs, or provide gamma information.

Alpha handling mode

Setting: preserve, premultiply, discard, or separate alpha plane
Effect: Premultiplying affects compositing; discarding loses transparency.
Recommendation: Preserve alpha where needed; prefer separate alpha plane for compositing control.

Dithering and quantization

Setting: none, ordered, Floyd–Steinberg, or custom
Effect: Dithering reduces banding when decreasing bit depth, at cost of added noise.
Recommendation: Use Floyd–Steinberg for best visual results when reducing color precision.

Gamma correction and linearization

Setting: apply gamma correction before conversion
Effect: Linearizing pixels before processing (e.g., downsampling or resizing) maintains more accurate results.
Recommendation: For any resampling or filtering, linearize (remove sRGB gamma), process, then reapply gamma.

Practical workflows

1) Preserve quality for archival or editing

Keep same bit depth and channels (e.g., 24 bpp -> 24 bpp).
Use tight packing, preserve alpha, tag as sRGB.
Avoid lossy quantization or change of color space.

2) Prepare images for embedded display (memory-constrained)

Choose a target bit depth that balances memory vs quality (e.g., 16 bpp RGB565).
Use Floyd–Steinberg dithering to minimize banding.
Convert color order and endianness to match the device.

Example command-line workflow:


BmpToRaw --input image.bmp --output image.raw --format RGB565 --dither floyd-steinberg --endian little --packed

3) Computer vision / ML preprocessing

Prefer single-channel grayscale or normalized float arrays.
Linearize sRGB -> convert to linear light, then normalize per-channel mean/std.
Use tight packing and document channel order.

4) Printing or high-fidelity display

Keep higher bit depth (prefer 32-bit float per channel if supported).
Preserve color profile or convert to the printer’s color space before dumping RAW pixel data.

Examples of conversions and expected visual changes

24 bpp BMP -> 24 bpp RAW (RGB): visually identical if channel order and stride match.
24 bpp BMP -> 16 bpp RAW (RGB565) + dithering: slight color banding minimized; reduced color gamut.
32 bpp BMP (with alpha) -> 24 bpp RAW: alpha discarded, background blending may be required beforehand.
sRGB BMP -> linear RAW (float32): better for image processing; appears darker if viewed without reapplying gamma.

Troubleshooting checklist

Colors look wrong: check channel order (RGB vs BGR) and endianness.
Image shifted or noise: check row stride/padding.
Washed/dark images: confirm color space/gamma assumptions.
Strange transparency: verify alpha handling (premultiplied vs straight).
Unexpected banding after bit reduction: enable dithering.

Performance and file-size considerations

RAW files are typically larger than compressed formats because they lack compression; choose lower bit depth or custom packing to save space.
For batch conversions, enable multi-threading if BmpToRaw supports it; process large images in tiled chunks to reduce memory use.
For streaming to hardware, match the device’s preferred pixel format to avoid runtime conversions.

Recommended default settings (balanced quality and compatibility)

Bit depth: same as source where possible (e.g., 24 bpp for standard BMP).
Channel order: RGB (confirm target).
Endianness: little-endian.
Row packing: tightly packed (no padding).
Color space: sRGB tag.
Alpha: preserve as separate alpha plane.
Dithering: Floyd–Steinberg when reducing bit depth.

Final notes

Careful choice of BmpToRaw settings preserves image fidelity and ensures predictable behavior in downstream systems. Always document the chosen format (bit depth, channel order, endianness, color space, stride) alongside the RAW file so consumers interpret bytes correctly. Small steps like correct gamma handling and dithering when quantizing produce large improvements in perceived quality.