Resize or compress an image to meet an upload limit

Pixels describe dimensions; bytes describe storage

Resizing changes the number of pixels. Compression changes how those pixels are encoded. In JustToolset, a 4000 × 3000 image resized to 1200 pixels wide with its proportions preserved becomes 1200 × 900. Its final byte size still depends on the picture and output settings.

Use the smallest change that meets the requirement

For a dimensions limit, use Image Resizer. For a byte limit with dimensions you want to keep, try Image Compressor. JPG and WebP quality settings can change the output size; Canvas PNG export does not use that quality parameter. A particular quality value does not promise a particular number of kilobytes.

1. Resize excessive dimensions while preserving proportions.
2. Export in a format accepted by the destination; compare JPG or WebP quality settings if appropriate.
3. Check the actual result size, download it and confirm that the receiving form accepts the file.

Reference: MDN: Canvas image export

Why the input has its own limits

JustToolset accepts images up to 20 MiB each, with a normal limit of 24 million pixels. Lower-resource devices use a 6-million-pixel limit; a reduced processing path may cap this at 2 million. The tool displays the applicable limits. A highly compressed image can have a small file size while still requiring substantial memory when decoded.

Do not discard the source

Repeatedly recompressing a previous JPG result can accumulate visible artifacts. Make each comparison from the source where possible. Enlarging a small image increases its dimensions but does not recover missing detail.

Use an explicit byte budget when the form gives one

The 50, 100, 200 and 500 KB tools preselect real maximums of 50,000, 100,000, 200,000 and 500,000 bytes. They search JPG or WebP quality, then reduce dimensions only when you allow it. A result is downloadable only if its actual encoded size meets the chosen maximum; it is never padded to an exact byte count.

If a form also requires minimum pixel dimensions, disable downsizing or check the final dimensions carefully. Meeting the byte budget alone does not establish that the form accepts the format or dimensions. The 1920 × 1080 and 1080 × 1080 resize pages instead start with exact crop-to-fill frames; borders can retain the whole image.

Reference: MDN: Blob size in bytes