8.1 Using Images

Image file types
You're probably already aware there are many different image format types available. Earlier in the course (section 3.4) you looked at how you could use the GIMP image editing program.

Here's we'll describe in more detail the different image types commonly used for images on the internet. Each of these is a compressed image type, meaning that smaller file sizes can be achieved, but with a possible reduction in quality.

GIF (Graphics Interchange Format): Usually used for line drawings and similar simple graphics. It only has support for 256 colours so generally doesn't work well for photographic images. It can support transparency, where the background may be transparent to allow the underlying web page colour to show through. GIF images can also be put together to create simple animations.

JPG or JPEG (Joint Photographics Network Group): Usually used for photographic images as it doesn't tend to work well with line drawings, simple graphics or lettering. No support for transparency.

PNG (Portable Graphics Network): May be slightly more compressed than a GIF image and can support 24 bit (16,777,216) colour. Supports transparency but not animations.

See some examples of how the image file type and compression can affect the resulting image. The advice at the end of this page says:
  • PNG is good option for transparency and non-lossy, smaller files. Larger files, not so much, unless you demand non-lossy images.
  • GIF is largely a novelty and only useful for animation, but can produce small 8-bit images.
  • JPG is still the king for photographs and photo-like images on the internet, but be careful, as your file can degrade with every save.