Image Formats
Wednesday, November 14, 2007
I thought it was only fitting that we discuss the very beginning of digital capture! There are basically two image formats that digital cameras can use to capture and record an image. The first is “jpg” and the second is “raw”. Raw format isn’t actually an image format per se, but rather a data file from the sensor itself. It is proprietary to each manufacturer and camera model, and is not available on most point and shoot type cameras. Additionally, special software (provided by third parties and the manufacturer) and techniques are needed to view the file. Raw files also need a fair bit of “post-processing” in order to optimize the images. Just to make matters worse, they must be converted to another format such as Tiff, to be worked on!
Jpg images on the other hand, are an agreed upon format and are the same between cameras and manufacturers, and can be viewed on any computer with existing software.
So, at this point you must be wondering why bother shooting raw files if they are such a hassle? The reason is image quality and the ability to optimize an image without losing quality. Most image parameters are set at the time of jpg capture. Right or wrong, what you see is what you get, and your ability to change image parameters or correct problems such as exposure or white balance is limited. Furthermore, a jpg is a compressed file format that loses information everytime you make a change and save it. A raw file on the other hand, can be saved in file formats that do not cause a loss of information such as Tiffs, and created anew as needed.
For example, the Nashville Warbler at the top of this page was accidentally overexposed by nearly a full stop. By shooting in raw format, I was able to correct this and salvage the image. Below is the jpg recorded at the time of exposure. If I had not been shooting in raw mode, there is no way I could have recovered the image.
As you can see, the image recovered quite nicely. In short, if you shoot in raw mode, you have much greater latitude to “fix” or optimize your images as you have the full set of data available to you.
Here is another example, in the first image I adjusted the jpg, many times, and saved it repeatedly. You can see how the colour shifted, posterization appears(lines in the background), and artifacts from jpg compression have appeared.
