1Upload the BMP images you want resized — work from the largest original you have rather than from a copy you already shrank once.
2Type a target width, a target height or a percentage, and leave the aspect-ratio lock on unless you deliberately want stretching.
3Run the resize; every file in the batch is taken to the same target in a single pass.
4Download the resized BMP file, or the whole set together as one archive.
Resize BMP FAQ
How does Resize BMP change the dimensions?
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Concretely, the pixels are resampled with a Lanczos filter and written back losslessly, so the only thing you lose is the detail that genuinely cannot fit in fewer pixels; nothing is added by the encoder on top. You give it a target width, a target height or a percentage, and it works from the original rather than from a previously resized copy.
Can I keep the aspect ratio, or force exact dimensions?
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Both. Lock the ratio and one dimension is derived from the other, which is what you want almost always. Unlock it and you get exactly the numbers you typed, at the cost of stretching — useful for a fixed slot, wrong for a photograph.
Does the source format affect the result of a resize?
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It does. BMP is essentially raw uncompressed RGB rows with a small header, so it is perfectly lossless and enormous — often 10-20x the size of the same image as PNG. That is what decides whether shrinking the file is purely a question of pixels or also a question of re-encoding.
Is there anything specific to BMP I should watch for?
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Yes — because nothing is compressed, a BMP is fast to read and edit but punishing to upload, and it carries no metadata to preserve. Worth checking before you resize a file you will not be able to regenerate.
What is the most common mistake when resizing BMP images?
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Upscaling. Enlarging cannot invent detail that was never captured, so the result is a soft version of the original at a bigger size. Always resize down from the largest source you have, and resize once rather than in stages.
What dimensions should I actually target?
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Match the slot it will live in. A full-width web hero rarely needs more than 1920 pixels wide, a content image 1200, a thumbnail 400, and doubling those numbers covers high-DPI screens. Anything beyond that is bytes nobody sees.
What can I upload to Resize BMP?
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PNG, BMP and TIFF are the lossless raster formats this handles directly, and lossy sources (JPG, WebP, GIF) work too if you want them in the same batch. Multi-page TIFFs are detected and handled page by page.
Is there a file size limit on Resize BMP?
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Yes: free accounts process images up to 5 MB each; lossless sources hit that ceiling sooner than photographs do, because nothing has been thrown away yet. If you are over it, converting to PNG first is often enough on its own — a BMP is routinely ten to twenty times the size of the identical image as PNG.
Will Resize BMP lower the quality of my BMP images?
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No. A lossless source round-trips bit-exactly, so unless you explicitly ask for a lossy output format the pixels that come back are the pixels that went in. That is the whole reason to keep working in this family while you are still editing.
Can I run Resize BMP on several BMP images at once?
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Yes — upload the set and they process in parallel under one set of settings. Lossless files are larger, so a big batch is bound by your upload speed rather than by the processing itself.
Does the alpha channel survive?
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Yes. PNG and TIFF carry a full 8-bit alpha channel and it is preserved end to end. It is only flattened if you deliberately target a format that has no alpha, in which case transparent pixels are composited onto white.
Does Resize BMP cost anything?
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No. Resize BMP runs free without an account and adds no watermark. Files are removed from the workers shortly after you download, and nothing about the image is retained.
