About

Bitmap files (.bmp) store pixel data uncompressed. A 1920×1080 image at 24-bit color depth occupies roughly 5.93 MB of raw data. That is 50× larger than the equivalent JPEG at 80% quality. Sending uncompressed bitmaps across networks wastes bandwidth. Storing them wastes disk space. This tool decodes the BMP on your device, re-encodes it into a lossy or lossless format, and lets you control the quality-to-size tradeoff directly. No data leaves your browser.

The compression factor depends on image content. Photographs with smooth gradients compress well under JPEG or WebP lossy encoding. Graphics with sharp edges and flat color regions benefit from PNG lossless compression. This tool reports the exact byte reduction so you can make an informed decision. Note: converting a BMP to lossy JPEG below quality 60% introduces visible artifacts around high-contrast edges. For archival work, prefer PNG or WebP lossless.

Formulas

The raw size of an uncompressed bitmap is calculated from its pixel grid and bit depth:

S_raw = W × H × D8

Where W = width in pixels, H = height in pixels, D = bit depth (typically 24 or 32 bits). BMP files also include a 54-byte header plus optional padding per row to align to 4-byte boundaries.

The compression ratio is:

R = S_original − S_compressedS_original × 100%

Where S_original = original file size in bytes, S_compressed = output file size in bytes. A ratio of 90% means the output is 10% of the original size.

When resizing by a scale factor k:

W_new = round(W × k), H_new = round(H × k)

Where k ∈ (0, 1] for downscaling. The canvas uses bilinear interpolation by default for smooth downsampling.

Reference Data

Format	Type	Compression	Transparency	Max Colors	Typical Ratio vs BMP	Best For
BMP	Uncompressed	None (RLE optional)	No (32-bit alpha rare)	16.7M	1:1	Raw pixel editing
JPEG	Lossy	DCT-based	No	16.7M	10:1 - 50:1	Photographs
PNG	Lossless	DEFLATE	Yes (alpha channel)	16.7M + alpha	2:1 - 5:1	Graphics, screenshots
WebP Lossy	Lossy	VP8-based	Yes	16.7M	15:1 - 60:1	Web delivery
WebP Lossless	Lossless	Predictive + LZ77	Yes	16.7M + alpha	3:1 - 8:1	Web graphics
BMP RLE8	Lossless	Run-Length Encoding	No	256	1.5:1 - 3:1	Simple 8-bit images
TIFF	Both	LZW / ZIP / None	Yes	16.7M+	1:1 - 5:1	Print, archival
GIF	Lossless (indexed)	LZW	1-bit	256	3:1 - 10:1	Simple animations
AVIF	Both	AV1-based	Yes	16.7M+	20:1 - 80:1	Next-gen web delivery
JPEG XL	Both	VarDCT / Modular	Yes	16.7M+	15:1 - 70:1	Future replacement
ICO	Lossless	PNG or BMP	Yes	16.7M	Varies	Favicons
SVG	Vector	XML text	Yes	Unlimited	N/A (vector)	Icons, logos

Frequently Asked Questions

BMP stores every pixel's color value without compression. A 1920×1080 image at 24-bit depth uses exactly 1920 × 1080 × 3 = 6,220,800 bytes of pixel data plus a 54-byte header and row padding. JPEG applies Discrete Cosine Transform (DCT) to 8×8 pixel blocks, discarding high-frequency detail the human eye barely perceives. This typically achieves 10:1 to 50:1 compression. PNG uses DEFLATE (LZ77 + Huffman coding) losslessly, achieving 2:1 to 5:1 on typical images.

Yes. JPEG is a lossy format. At quality 85-95%, artifacts are generally imperceptible to the human eye. Below quality 60%, blocking artifacts appear around sharp edges. Each re-save of a JPEG introduces generational loss. If you need pixel-perfect fidelity, convert to PNG or WebP lossless instead. This tool lets you preview the result before downloading so you can judge the tradeoff.

For photographs: WebP lossy at quality 75-80% typically produces files 25-35% smaller than equivalent-quality JPEG. For graphics with flat colors: PNG often beats JPEG because JPEG's DCT creates artifacts on sharp edges while PNG's DEFLATE handles repetitive patterns efficiently. WebP lossless beats PNG by roughly 20-25% on average according to Google's comparative studies.

32-bit BMP files have an alpha channel. If you convert to JPEG, the alpha channel is discarded and transparent pixels render as black or white (depending on canvas background). To preserve transparency, choose PNG or WebP as the output format. This tool composites against a white background when JPEG is selected.

Browsers cannot encode BMP output natively. The Canvas API supports toBlob() for JPEG, PNG, and WebP only. To reduce BMP size without format change, you would need RLE encoding or external tools. This tool converts to a compressed format, which is the practical solution. If you need BMP specifically, resize the image to reduce pixel count, then use an external BMP encoder.

Significantly. Halving both dimensions (scale factor 0.5) reduces pixel count by 75%. Combined with lossy encoding, you can achieve 95%+ file size reduction. However, downscaling is destructive and irreversible. Always keep the original file. The tool shows the output dimensions before you download.

No. All processing occurs locally in your browser using the Canvas API and Blob API. The image is loaded into an HTML5 Canvas element, re-encoded client-side, and the result is generated as a downloadable Blob URL. No network requests are made. You can verify this by disconnecting from the internet and using the tool.