When you take photos with the Canon Digital SLR each photo is saved as a digital file on the digital camera memory and most likely is later transferred to your computer. Like any other computer file digital photo files can also have different formats. Every computer file is comprised of a long series of bits and bytes. A file format is a description of the meaning of those bits and bytes or in other word a file format explains how the file should be read and interpreted. If you like you can compare a files and file format to writing text. When you write a sentence you basically type a series of characters. They are meaningless unless you know that they are in a format called English and that specific combinations of characters have certain meanings.

There are a few common formats for storing digital photos each with its advantages and disadvantages. Usually digital cameras like the Canon Digital SLR let you choose which format you would like to use. The first big difference between format types if the compression method used if at all. But first lets quickly review what compression is and what it is needed. A digital photo is a collection of pixels. Each pixel represents a tiny portion of the whole digital photo and has a color and intensity attribute. Usually pixels are stored in true color as a three bytes triplet. Each byte represents an intensity of one prime color. Mixed together they provide an exact color and intensity representation of that pixel.

The size of a digital photo file depends on the resolution in which it was taken also known as the number of mega pixels. The number of mega pixels grows as cameras get more advanced. A common 8 mega pixel camera generates eight million pixels for every single digital photo that you take. That is quite a lot of pixels and with 3 bytes per pixel storing each digital photo will consume 8,000,000 pixels times 3 bytes = 24,000,000 bytes also known as 24 megabytes. This is a very big file. It will result in having less space on your camera memory card for storing photos, it is hard to process, slow to send over email, slow to upload to a web site and so on.

Fortunately there are efficient way to store digital photos that consume much less disk space. In every photo that you take there is some redundancy and inefficiency. Compressing a digital photo is a method that removes redundancy and details that are considered not important or not noticeable by the viewer. In our previous example a 24 megabytes digital photo file could easily be compressed to consume only 3 megabytes with hardly any noticeable quality degradation.

The compression method described above is also known as lossy compression since some information although hardly noticeable was lost. There are other compression method with are known as lossless and which create a compressed file that can be uncompressed to exactly the original file. They are however less efficient and can not achieve such high compression ratios to convert a 24 megabytes file to a 3 megabytes file.

Most cameras allow you to choose between two photo formats, compressed or RAW. Raw format is simply the uncompressed version of the digital photo and it consumes a lot of space. Professional photographers use RAW format as it provides better quality when processing the photo later on. For all other photographers a compressed JPEG file is a better choice. Digital cameras like the Canon Digital SLR also let you set the compression ratio. The higher the ratio the smaller the file but at the same time the more degraded the quality of the compressed image.