GIF サイズ変更

Type a width in pixels or use one of the presets: 480, 320 or 240 px wide. With “Keep aspect ratio” on, the height follows the shape of each GIF, so a batch of wide and square animations can all be set to 320 px wide without stretching any of them. Turn the lock off to give an exact width and height, for example 128×128 for a square emoji slot; non-matching shapes are then stretched to fit.

The largest side you can set is 4096 px. Making a GIF bigger is possible but adds no detail: the frames are interpolated, edges get softer and the file grows.

Before scaling, each frame is composited: transparent areas, partial frames and disposal methods are applied first, so what you resize is the picture you actually see, not the raw patches stored in the file. When shrinking, each output pixel is the average of the source pixels it covers (area averaging), which keeps thin lines and text readable and avoids the jagged look of nearest-neighbour scaling. Averaging is done with alpha taken into account, so transparent backgrounds do not leave dark fringes around a sticker.

The resized frames are written with up to 256 colours each and every frame kept. Only the pixels that change between frames are stored, which keeps the file close to the smallest it can be at full quality.

Fewer pixels do not always mean a smaller file. On our 320×200, 30-frame test GIF (429,740 bytes, every frame written in full), resizing to 240×150 in Chrome produced 149,511 bytes with all 30 frames and the same 1.2-second length. Most of that drop came from storing only changed pixels; the smaller picture alone would not have done it, because averaging creates new in-between colours that need palette entries of their own.

If you need the file smaller still, run the result through the GIF compressor afterwards and reduce the colours, or drop frames there. When a resized GIF does end up larger than the original, for example after enlarging, the tool tells you.

A README or documentation demo usually reads well at 480 to 800 px wide; GitHub accepts GIFs up to 10 MB in issues and pull requests. Chat reactions look right at 240 to 320 px. Custom emoji in chat apps such as Discord are small squares with a much tighter file limit than attachments, so resize to the square size first and then compress. Batch up to 10 GIFs of 50 MB each; they are processed one after another and you can download each or all of them as a ZIP.