Image File Formats Colour Depth. Note that rgba is not available for all image formats check the list above for details. Nevertheless it is one of the lossless image formats so the file sizes will be pretty large.
Give preference to jpeg for working with images on the web. Bmp jpg tif png psd ico pcx tga etc. Many specialized image file types like camera raw files are tif file format but using special proprietary data tags.
When it comes to talking about colour depths there is an old school mindset that can sometimes bring confusion.
Gif is still a popular image format on the internet because image size is relatively small compared to other image compression types. This means it has a colour depth of 1 bit. 8 bit 256 levels most common for on screen graphics and video. Give preference to jpeg for working with images on the web.