Why a JPG from a GIF
People ask for this when a form, a marketplace, a print shop or a document template accepts JPG and rejects GIF, or when they want a small preview picture of an animation. The conversion takes the first frame, so what you get is a still of how the animation begins.
A GIF and a JPG have almost nothing in common inside. A GIF is a palette picture with sharp edges. A JPG compresses a picture in blocks and discards detail, which suits photographs and not sharp graphics. That difference decides whether the conversion saves space.
Photographic frames and flat graphics behave differently
We converted eight test GIFs and the result depended on the kind of picture. A photo squeezed into 256 colours, 640 by 480 pixels, went from 212.6 KB to 78.7 KB, 63 percent smaller. A smooth gradient went from 21.6 KB to 3.3 KB (85 percent smaller), and a 160 by 120 frame with gradients and a drawing on it was 83 percent smaller. Flat artwork went the other way: a four colour logo grew from 2.1 KB to 7.5 KB (262 percent larger), the same logo on a transparent background from 1.6 KB to 5.5 KB, and a small three colour graphic with a transparent background became more than five times the size of its GIF. Flat colour is exactly what GIF stores well and JPG stores badly.
The picture changed too. Against an exact copy of the first frame placed on the background colour, the graphic had an average error of about 7 levels out of 255, concentrated at its sharp edges, and the smooth frame about 1.5. A GIF has at most 256 colours and a JPG has many more: the photo's 256 colours became 50,619 different colours in the JPG, and the four colour logo 3,080. They are compression noise, not new detail. In the logo, 5.2 percent of the pixels ended up more than 4 levels from any of its four colours. As PSNR against the GIF, the photo scored 34.0 dB, the flat logo 34.9 dB and the gradient 59.0 dB. For graphics, logos and screenshots saved as GIF, GIF to PNG is the cleaner choice.
Transparent GIFs and the background colour
A GIF can name one colour as transparent. A JPG cannot be see-through, so the converter fills every transparent pixel with the colour in the background control. We set it to a yellow and measured the flattened area: its average was the chosen colour to within a fraction of a level out of 255.
Choose the colour with the page in mind. Dark artwork on a transparent background looks right on white. Light artwork, such as a white logo, vanishes on white, so pick a dark colour for it. The control takes a hex code, a swatch or the colour picker.
Quality for a still from an animation
The default of 90 is a good start for photographic frames. Below about 75 you may see blocks, and from 95 up the encoder keeps colour at full resolution, which matters for coloured text and thin lines. A frame that has been through a GIF palette often has flat blotches that show blocking sooner, so check one result before you convert a long list.
The frame is converted at its own size. If you need it smaller as well, shrink it afterwards, because converting twice with lossy formats adds loss each time.