Image 1, unedited.
First I shall be dealing with the GIF format. When changing to this format in Photoshop, the image is given a certain amount of colours depending on the quality required of the image. The range of colours goes from 2 to 256. I created multiple copies of the image with varying amounts of colours to investigate how the amount changes the quality and file size.
As can be seen from the graph, the increase in colours creates a steady increase in file size. However, viewing the images themselves is a different story. Many of the smaller sized images are not suitable for use on the web, as they are of very poor quality.
Image with 4 colours. Image with 64 colours.
The image on the left would most certainly not be suitable for use on the internet, while the image on the right would be just about passable.
It is also possible to keep a similar quality while dropping the file size even further using Dithering. this scatters the pixels around the borders of the colours to try and create a new colour. This improves the quality by making the colours blend smoothly.
16 colours without Dithering.
16 colours with Dithering
Dithering allows images to look a higher quality than they actually are without sacrificing too much file size.
When creating JPEG images in photoshop, the main thing which is affected is the quality. To reduce the file size, the quality must be changed from 100% downwards. Initially, there is very change within the image while the file size drops drastically. This is useful for using images on the internet.
As can be seen from the graph, dropping the image down to 60% quality reduces the file size to 1/5th of a 100% quality JPEG.
The image on the left is of 60% quality, while the image on the right is of 100% quality. There is very little visible difference between the pictures, despite the drastic change in file size.
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