It builds an animated GIF from either a set of pictures (one picture per frame) or a short stretch of a video. For pictures you can reorder the frames, give each its own delay, and remove the ones you do not want. For a video you set a start and an end, choose how many frames per second to take, and the frames are read from the clip in your browser. Then you choose the width, how frames of another shape are fitted, the number of colours, the palette, dithering and the loop, and the tool encodes the GIF with its own encoder: the colour reduction, the LZW compression and the file layout are all written here and run on your device. Nothing is uploaded.
A GIF stores at most 256 colours per frame and compresses each frame with LZW, a method from 1984 that is good at long runs of the same colour and poor at photographic detail. That is why a few seconds of camera footage can become a GIF of several megabytes while the same clip as MP4 is far smaller. The article on how GIFs work has the numbers. The tool uses the tricks that matter most:
- One shared palette for the whole animation, chosen by median cut over pixels from every frame. It is smaller than a palette per frame and avoids colours flickering between frames. Choose one palette per frame when the scenes are very different.
- Store only what changes. After the first frame, each frame keeps just the rectangle that changed, and inside it the pixels that look the same as before become transparent. A talking head or a screen recording where little moves shrinks dramatically.
- Repeated frames are merged: if a frame looks exactly like the previous one, the previous one is simply shown longer.
- Fewer colours (128, 64, 32) make smaller files; flat graphics and screenshots often look identical at 64.
- Dithering mixes palette colours in a fine pattern so gradients do not show bands. It looks better on photos but makes the file larger, because the pattern is noise to LZW.
Timing, without surprises
GIF delays are stored in hundredths of a second. Browsers treat delays of 0 or 1 hundredth as 10 hundredths (100 ms), so the shortest delay that really plays fast is 20 ms, which is 50 frames per second; the tool never writes less. Frame rates that do not divide 100 evenly are handled by carrying the remainder: 15 fps becomes 70, 60, 70, 70, 60, 70 ms, so one second of video is still exactly one second of GIF. The loop setting writes the standard NETSCAPE block: forever, once, or a number of plays.
Limits and tips
A GIF holds at most 300 frames here, and frames × width × height is capped so the browser does not run out of memory (at 480 × 270 that is all 300 frames; at 800 × 800, 62). A 480-pixel-wide GIF at 10 frames per second is a good balance for chat apps. Keep clips short; three to five seconds is the sweet spot. For anything longer, or with sound, a video file is the better format: the screen recorder saves WebM or MP4, and the image toolkit can resize the pictures first.
