Introduction
Update: 01-08-2014. This set of articles are one of the oldest on my website written back in 2000 but the information is still relevant and useful. Given the speed of the modern Internet there is not much talk about image compression but it's amazing how many times the subject still comes up. Ever wonder why pictures on Facebook or the Ipad are not as good as you remember? Background picture compression. What bothers me is not that the pictures are compressed, but rather both services hide the fact. Hopefully this is a trend that will someday disappear. Until then I hope the following will give you an idea of how graphics and compression work.
If you do not currently have a good understanding of computer graphics and file formats I would highly suggest reading the articles in order. Most articles require concepts from the previous articles. At the end of the articles are various topics I have listed under the heading "support files". In the course of reading the articles I have referenced these topics as needed for people who may need further background information. These articles may be read in any order and I would suggest browsing the titles for any topic you may wish to refresh.
Note: If you are trying to understand how file formats and compression work, do be careful of Photoshop. Photoshop does not let you count or modify the number of unique colors in an image which is a major part of file compression. Also, some file options are not available in Photoshop. I would recommend programs like IrfanView, Paint Shop Pro, or any program that has both a "count color" tool and a "color depth tool". If all you have is Photoshop, use the "Save for Web" option which will give you more options saving GIF and JPEG files.
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1. Overview 2. Bitmap and Vector Graphics Bitmap Images Vector Images Resolution and Scaling 3. Bitmaps In Detail The BMP format In Detail Bitmaps and the RLE Compression 4. Bits and the Number of Colors Bits and Binary Numbers The Number of Colors Bit Depth and the Number of Colors Other Useful Color Information 5. Reducing the Number of Colors How many colors do you need? Niagara Falls Image A Slight reduction in color 24 bit to 8 bit BMP and GIF Formats Color reduction from 256 to 16 colors Images with no single primary color Balloon and Tower Images Images with No Single Primary Color Color Banding Dither Random Examples |
6. The GIF File Format Index Color Method Transparency Animation Interlaced and Non-Interlaced A Final Word GIF Reference Article 7. File compression and Winzip File compression and Winzip LZW Compression 8. File compression and Data Loss "Lossy" and "Lossless" Compression Color Reduction Quality Reduction 9. The JPEG File Format About Compression Method Outline Text Description Details Important Points Examples and Comments 10. The TIFF File Format About |
Support Information
File Formats Quick List
BMP, GIF, JPG, TIFF
Colors and the Computer
The RGB Color System
Additive and Subtractive Color
Creating this in Adobe Photoshop
Color Space and the Computer
Binary Numbers
What's a Bit? Binary Numbers
Kilobytes, Megabytes, Gigabytes, O My
How the computer calculates file size
File Sizes
A File Size Comparison between BMP, TIFF, GIF and JPG.