JPEG, GIF… or else? Part 2: Formats

The examples in my previous post were probably too simple to guide you in your work, but before we look at more tricky cases, let me tell you more about those formats we used.

GIF files

The GIF format is pretty old, and this explains one of its major feature: it stores only 256 colours in the image.
That is why the photograph we saved in this format had the blue sky painted in stripes of colour:Photo in GIF format

 
The editor had to figure out which colours to sacrifice, out of a million or so on the photo.

Sometimes you can get better results using so called “dithering” option, when saving file in GIF format: IM13, but let’s face it: the image is distored anyway: IM14.

If your image has no more than 256 colours, GIF file will store the entire image in a compressed form, and without any distortions.

Other small useful facts about GIF format: these images can be animated, and they can contain transparent areas. But since we are just talking about quality of images, I won’t go into more details.

JPEG files

The JPEG format has been designed with photographs in mind, and that is what it does best.
When you save an image as JPEG file, your editor will ask you what quality you want to achieve, or what level of compression. The higher compression, the smaller image file will be, but also the less perfect it will becode.
You need to know that in any case, the image you save on disk will loose some small details in the process.
So this format is to be used for “publishing” images, and not for storing the originals (unless, of cause, your originals were created as JPEG files in the first place).

PNG files

The PNG format is relatively more modern, and this explains its strengths and weaknesses.
It provides quite decent compression in most cases, it does not have limitation on the number of colours, but… it may be not supported by some old software.

I do not consider it a big limitation though: the only case where you would be weary about using PNG, would be when you publish your image, and you want to be sure that absolutely everyone in your audience can properly see it.
And the only users in your audience, who may have problems with your PNG file, are those with older Internet Explorer browsers.  PNG format was supported by IE almost from the start, but the browser had various problems with this format in most versions.

Other formats

There are dozens of them. Why did I mention BMP format in Part 1 of this topic? Because I still see it in use.
BMP files are not compressed at all. They are huge. Microsoft originally included compression in the format specification, but did not implement the compression in its tools.

Mind you, that there are also so-called “vector” graphics formats, but that’s completely different topic

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