Does cropping a BMP reduce quality?

No. Cropping is a pure pixel-window operation — the bytes for the kept region are written to the output unchanged. Because BMP doesn't go through a transform-based encoder (unlike JPG), there is no re-compression artifact added by the crop itself.

How much does cropping shrink a BMP?

File size is roughly proportional to retained pixel count. Cropping to 50% of the area cuts size by about 50%; cropping to a quarter cuts it to about a quarter, plus a fixed ~54-byte header. This is a sharper size lever than any compression option, because the source had no compression to remove.

Can I keep transparency when cropping a BMP?

Only if your input is a 32-bit BMP. The alpha channel was added in BITMAPV3INFOHEADER and formalized in BITMAPV4HEADER — older 24-bit BMPs simply have no alpha to preserve. If you need transparency, crop and export to PNG with BMP to PNG instead.

What bit depth should I pick for the output?

24-bit (the BMP default for color photos) keeps full color fidelity. 8-bit (Recommended) uses an indexed palette of 256 colors and is fine for screenshots, UI graphics, and diagrams — file size drops about 3×. 1-bit (Black & White) is for fax-style or monochrome scans and is the smallest by far. 16-bit is rarely useful unless a specific legacy tool requires it.

Why is my cropped BMP still bigger than the original JPG of the same scene?

Because BMP is uncompressed by default. Even a tightly cropped BMP carries 3 bytes per pixel (24-bit) with no entropy coding, while a JPG of the same dimensions runs through DCT, quantization, and Huffman coding. If size matters more than format compatibility, crop and convert to BMP to JPG or BMP to PNG.

Can I crop a BMP and combine it with image compression?

Yes. Under "Image Compression" pick a Quality Preset, set Target file size (%), enter a Specific file size in MB, or move the Image Quality (%) slider. Combined with a smaller crop area, you can take a 24 MB 4K BMP down by an order of magnitude. If you want pure size reduction without changing dimensions, see Compress BMP.

Will the BMP still open in legacy Windows software after cropping?

Yes — the output uses the standard BITMAPINFOHEADER layout that every Windows version since Windows 3.0 (1990) reads. If your target is a very old or embedded tool that requires a specific bit depth, set Bit Depth explicitly so the output matches what that tool expects.

Can I crop several BMP files at once with the same dimensions?

Yes. Upload a batch and apply the same width, height, and X/Y crop to all of them. Useful for trimming a folder of screenshots that share a fixed UI chrome, or for cropping a sequence of scientific captures to a common region of interest.

Should I crop as BMP or convert to a modern format first?

If the downstream consumer is a legacy Windows app, point-of-sale system, embedded HMI, or a tool that explicitly demands .bmp, keep the output as BMP. For everything else — web, email, mobile, modern documents — crop and convert to PNG (lossless, far smaller) or JPG (smallest, lossy). Adobe and Microsoft both recommend PNG over BMP for general-purpose lossless storage today.

Crop BMP

Crop BMP bitmap images online for free. Trim to exact dimensions with optional compression.

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