BMP to WebP

bars-32x16.bmp is a 24-bit bitmap. The browser decoded it and encoded WebP at quality 80 and again at quality 60. Both downloads are 32 by 16 and about 0.6 KB. Flat red and blue give the encoder almost nothing to cut, so the two qualities land on the same small file. A photographic bitmap will not behave like that. Read the size line on the photograph. The grid does not change. A browser that cannot encode WebP stops instead of renaming a PNG. These bars are opaque, so they do not show whether a transparent BMP pixel, which this 24-bit file does not have, would survive. The bitmap stays on disk.

Keep the bitmap until the WebP opens and the size line on a real photograph is one you want. The bars only prove 32 by 16 and a real WebP container. They are a bad teacher of savings. The page does not upload the bitmap, and it does not rename a PNG when WebP encoding is missing.

Leave the bitmap in the folder until a photographic BMP, not these bars, has shown whether quality 60 is actually smaller. The bars are 32 by 16 and about 0.6 KB at both settings. That match is the grid check. It is not a savings claim. The browser wrote a real WebP. If encoding WebP is missing, the page stops. The uncompressed bitmap remains the file an old program can still open.

A photographic bitmap is the file that teaches quality. These bars do not. They are 32 by 16, red then blue, and both WebP settings landed near 0.6 KB. That tells you the container is WebP and the grid survived. It does not tell you how many kilobytes a scan will lose at quality 60. Open one scan, read the size line, and only then delete the bitmap. If the browser cannot encode WebP, the page stops. A renamed PNG would be a lie, and this page will not write one. The bitmap itself is never uploaded.

Do the size comparison on a real photograph stored as BMP. These bars are the control: 32 by 16, about 0.6 KB, WebP at both qualities. They prove the format and the grid. They do not prove the savings. When the photograph’s size line is the one you want, then you can drop the bitmap. Until then, keep both. A browser without a WebP encoder is told to stop.

Work in this order. Open the bitmap. Press convert at quality 80. Read the size and the 32 by 16 grid. Change the quality to 60 and read the size again. On these bars the two sizes match, near 0.6 KB, so the quality slider is not doing visible work. On a scan of a printed page the two sizes will separate, and the lower quality may soften the type. Stop at the quality that is still readable. Only then is the bitmap safe to set aside. If the button says the browser cannot write WebP, believe it. Do not rename a PNG and call it WebP. The original bitmap is still in the folder the whole time, because this page never uploads it and never deletes it.

A PNG of the same bitmap is BMP to PNG.

Bitmap at WebP quality 80

Inputs: b2w-f: bars-32x16.bmp | b2w-q: 80

On this page, take bars-32x16.bmp, then 80 and press Convert. Flat colours may not shrink between the two qualities.

Result: BMP to WEBP: 32×16. 0.6 KB

Bitmap at WebP quality 60

Inputs: b2w-f: bars-32x16.bmp | b2w-q: 60

On this page, take bars-32x16.bmp, then 60 and press Convert. Flat colours may not shrink between the two qualities.

Result: BMP to WEBP: 32×16. 0.6 KB

What size is the WebP?

32 by 16, matching the bitmap.

Did quality 60 shrink the bars?

Not in a way that shows. Both files are about 0.6 KB.

Who encodes WebP?

The browser. A missing encoder stops the page.

Is the bitmap uploaded?

No.

Will a scan match this size?

No. These bars are two colours.

Is alpha preserved?

This 24-bit bitmap has no alpha to preserve.