About

Bitmap files (.bmp) use uncompressed pixel data, resulting in file sizes often 10× to 50× larger than modern formats. A 1920×1080 24-bit BMP consumes approximately 6.2MB, while equivalent WebP at quality q=80 typically requires 150−300KB. This converter uses your browser's native WebP encoder, processing entirely client-side with zero server uploads. Note: conversion quality depends on browser implementation; Chrome and Firefox produce optimal results, while Safari's WebP support varies by version.

WebP employs VP8 lossy compression with predictive coding and discrete cosine transforms, achieving superior compression ratios compared to JPEG at equivalent perceptual quality. For archival BMP files from legacy systems, scanning equipment, or screenshot tools, conversion to WebP reduces storage requirements by 85−95% while maintaining visual fidelity. The quality parameter q controls the quantization level: values below 50 introduce visible artifacts in gradients and text edges.

Formulas

The conversion process maps raw bitmap pixel data through WebP's VP8 lossy encoder. File size reduction depends on image complexity and quality setting:

Compression Ratio = Size_BMP − Size_WebPSize_BMP × 100%

Where Size_BMP represents the original bitmap file size in bytes, and Size_WebP is the output WebP blob size. The quality parameter q maps linearly to the encoder's quantization level:

q_encoder = q_user100

BMP uncompressed size can be calculated from dimensions and bit depth:

Size_BMP = W × H × bpp8 + Header

Where W = width in pixels, H = height in pixels, bpp = bits per pixel (24 for RGB, 32 for RGBA), and Header = 54−138 bytes depending on BMP version.

Reference Data

Format	Compression	Typical Size (1080p)	Transparency	Animation	Browser Support	Best Use Case
BMP	None (Raw)	6.2MB	Limited (32-bit)	No	Universal	Legacy systems, raw capture
WebP (Lossy)	VP8 DCT	150−300KB	Yes (Alpha)	Yes	95%+ modern	Web images, photos
WebP (Lossless)	Predictive	1.5−3MB	Yes (Alpha)	Yes	95%+ modern	Graphics, screenshots
JPEG	DCT 8×8	200−500KB	No	No	Universal	Photographs
PNG	DEFLATE	2−5MB	Yes (Alpha)	No	Universal	Graphics, transparency
GIF	LZW	500KB−2MB	1-bit only	Yes	Universal	Simple animations
AVIF	AV1 Intra	80−150KB	Yes (Alpha)	Yes	~85% modern	Next-gen web images
TIFF	Optional LZW	6−20MB	Yes	No	Limited	Print, archival
BMP Bit Depth Variants
1-bit BMP	None	253KB	No	No	Universal	Monochrome scans
4-bit BMP	None	1.0MB	No	No	Universal	16-color palettes
8-bit BMP	None	2.1MB	No	No	Universal	256-color indexed
16-bit BMP	None	4.1MB	No	No	Universal	High-color legacy
24-bit BMP	None	6.2MB	No	No	Universal	True color standard
32-bit BMP	None	8.3MB	Yes (Alpha)	No	Universal	RGBA with alpha
WebP Quality Guidelines
Quality 100	Minimal lossy	400−600KB	Near-lossless, archival quality
Quality 80−90	Balanced	150−300KB	Recommended for photographs
Quality 60−75	Aggressive	80−150KB	Web thumbnails, previews
Quality 30−50	High compression	30−80KB	Low-bandwidth, visible artifacts
Quality <30	Extreme	<30KB	Not recommended, severe degradation
Compression Ratio Benchmarks (24-bit BMP to WebP q=80)
Photograph	95−98% reduction		Complex textures compress well
Screenshot (UI)	90−95% reduction		Sharp edges, flat colors
Digital Art	85−92% reduction		Gradients may show banding
Scanned Document	88−94% reduction		Text edges remain sharp at q≥75
Medical Imaging	Not recommended		Use lossless formats for diagnostics

Frequently Asked Questions

WebP lossy compression uses DCT (Discrete Cosine Transform) and predictive coding that approximates pixel values rather than storing them exactly. At quality settings below 90, you may notice softening in high-frequency details like text edges or fine textures. For pixel-perfect conversion, WebP lossless mode is required, though browser Canvas API only exposes lossy encoding. If exact fidelity is critical, consider PNG as an intermediate format.

The converter checks for WebP support using canvas.toBlob() feature detection. Safari versions before 14 (macOS Big Sur) lack WebP encoding support and will display an error. Chrome, Firefox, and Edge have supported WebP encoding since 2014-2018. If unsupported, the tool offers PNG fallback encoding which is universally supported.

Yes. The Canvas API preserves alpha channel data when loading 32-bit BMP files. WebP fully supports 8-bit alpha transparency, and the encoder maintains this during conversion. The resulting WebP file will have proper transparency without the file size overhead of PNG.

The tool limits input to 50MB to prevent browser memory issues. However, practical limits depend on your device's RAM. A 50MB BMP at 24-bit depth represents approximately 8500×8500 pixels. Devices with less than 4GB RAM may struggle with files exceeding 30MB. Conversion happens entirely in browser memory, requiring roughly 3× the file size in available RAM.

Compression efficiency varies by image content. Photos with complex textures achieve 95-98% reduction, while screenshots with sharp edges and flat colors may only reach 85-92%. Additionally, browser WebP encoders may differ from standalone tools like cwebp. Chrome's encoder tends to produce slightly larger files than Google's reference implementation at equivalent quality settings.

No. BMP files rarely contain EXIF data (it's not part of the standard specification). When present in non-standard BMPs, the Canvas API strips all metadata during rendering. The output WebP contains only pixel data. For workflows requiring metadata preservation, use dedicated tools like ImageMagick or ExifTool post-conversion.