[image] What are the different usecases of PNG vs. GIF vs. JPEG vs. SVG?

When should certain image file types be used when building websites or interfaces, etc?

What are their points of strength and weakness?

I know that PNG & GIF are lossless, while JPEG is lossy.
But what is the main difference between PNG & GIF?
Why should I prefer one over the other? What is SVG and when should I use it?

If you don't care about each and every pixel, should you always use JPEG since it's the "lightest" one?

png has a wider color pallete than gif and gif is properitary while png is not. gif can do animations, what normal-png cannot. png-transparency is only supported by browser roughly more recent than IE6, but there is a Javascript fix for that problem. Both support alpha transparency. In general I would say that you should use png for most webgraphics while using jpeg for photos, screenshots, or similiar because png compression does not work too good on thoose.

As pointed out by @aarjithn, that WebP is a codec for storing photographs.

This is also a codec to store animations (animated image sequence). As of 2020, most mainstream browsers has out of the box support for it (compatibility table). Note for WIC a plugin is available.

It has advantages over GIF because it is based on a video codec VP8 and has a broader color range than GIF, where GIF limits to 256 colors it expands it to 2²⁴ = 16777216 colors, still saving significant amount of space.

I usually go with PNG, as it seems to have a few advantages over GIF. There used to be patent restrictions on GIF, but those have expired.

GIFs are suitable for sharp-edged line art (such as logos) with a limited number of colors. This takes advantage of the format's lossless compression, which favors flat areas of uniform color with well defined edges (in contrast to JPEG, which favors smooth gradients and softer images).

GIFs can be used for small animations and low-resolution film clips.

In view of the general limitation on the GIF image palette to 256 colors, it is not usually used as a format for digital photography. Digital photographers use image file formats capable of reproducing a greater range of colors, such as TIFF, RAW or the lossy JPEG, which is more suitable for compressing photographs.

The PNG format is a popular alternative to GIF images since it uses better compression techniques and does not have a limit of 256 colors, but PNGs do not support animations. The MNG and APNG formats, both derived from PNG, support animations, but are not widely used.

The main difference is GIF is patented and a bit more widely supported. PNG is an open specification and alpha transparency is not supported in IE6. Support was improved in IE7, but not completely fixed.

As far as file sizes go, GIF has a smaller default color pallet, so they tend to be smaller file sizes at first glance. PNG files have a larger default pallet, however you can shrink their color pallet so that, when you do, they result in a smaller file size than GIF. The issue again is that this feature isn't as supported in Internet Explorer.

Also, because PNGs can support alpha transparency, they're the only option if you want a variation of transparency other than binary transparency.

GIF based on a palette of 256 colours per image (at least in its basic incarnation). PNG can do "TrueColour", i.e. 16.7 Million colours out of the box. Lossless PNG compresses better than lossless GIFs. GIF can do "binary" transparency (0% opacity or 100% opacity). PNG can handle alpha transparencies.

All in all, if you don't need to use Alpha-transparent images and support IE6, PNG is probably the better choice when you need pixel-perfect images for vector illustrations and such. JPG is unbeatable for photographs.

JPEG will have poor quality around sharp edges etc. and for this reason it is unsuitable for most web graphics. It excels at photographs.

Compared to GIF, PNG offers better compression, larger pallette and more features, including transparency. And it is lossless.

There is a hack that can be done to use GIF images to show true color. One can prepare a GIF animation with 256 color paletted frames with 0 frame delay and set the animation to be shown only once. So, all frames could be shown at the same time. At the end, a true colored GIF image is rendered.

Many software is capable of preparing such GIF images. However, the output file size is larger than a PNG file. It must be used if it is really necessary.

Edit: As @mwfarnley mentioned, there might be hiccups. Still, there are still possible workarounds. One may see a working example here. The final rendered image looks like that:

full-color-gif-image

GIF has 8 bit (256 color) palette where PNG as upto 24 bit color palette. So, PNG can support more color and of course the algorithm support compression

JPEG is not the lightest for all kinds of images(or even most). Corners and straight lines and plain "fills"(blocks of solid color) will appear blurry or have artifacts in them depending on the compression level. It is a lossy format, and works best for photographs where you can't see artifacts clearly. Straight lines(such as in drawings and comics and such) compress very nicely in PNG and it's lossless. GIF should only be used when you want transparency to work in IE6 or you want animation. GIF only supports a 256 color pallete but is also lossless.

So basically here is a way to decide the image format:

• GIF if needs animation or transparency that works on IE6(note, PNG transparency works after IE6)
• JPEG if the image is a photograph.
• PNG if straight lines as in a comic or other drawing or if a wide color range is needed with transparency(and IE6 is not a factor)

And as commented, if you are unsure of what would qualify, try each format with different compression ratios and weigh the quality and size of the picture and choose which one you think is best. I am only giving rules of thumb.

GIF is limited to 256 colors and do not support real transparency. You should use PNG instead of GIF because it offers better compression and features. PNG is great for small and simple images like logos, icons, etc.

JPEG has better compression with complex images like photos.

If you opt for JPEG, and you're dealing with images for a website, you may want to consider the Google Guetzli perceptual encoder, which is freely available. In my experience, for a fixed quality Guetzli produces smaller files than standard JPEG encoding libraries, while maintaining full compatibility with the JPEG standard (so your images will have the same compatibility as common JPEG images).

The only drawback is that Guetzli takes lot of time to encode.. but this is done only once, when you prepare the image for the website, while the benefits remains forever! Smaller images will take less time to download, so your website speed will increase in the everyday use.

As of 2018, we have several new formats, better support for previous formats and some clever hacks of using videos instead of images.

For photographs

jpg - still the most widely supported image format.

webp - New format from google. Good potential, though browser support is not great.

For Icons and graphics

svg - whenever possible. It scales well in retina screens, editable in text editors and customisable via JS/CSS if loaded in DOM.

png - if it involves raster graphics (ie when created in photoshop). Supports transparency which is very essential in this use-case.

For Animations

svg - plus css animations for vector graphics. All advantages of svg + power of css animations.

gif - still the most widely supported animated image format.

mp4 - if animated images are actually short video clips. Twitter / Whatsapp converts gifs to mp4.

apng - decent browser support (i.e. no IE, Edge), but creating it is not as straightforward as gifs.

webp - close to using mp4. Poor support

This is a nice comparison of various animated image formats.

Finally, whichever be the format, make sure to optimize it - There are tools for each format (eg SVGO, Guetzli, OptiPNG etc) and can save considerable bandwidth.