Sunday, May 1, 2005

A RAW deal: Using the RAW image format


By John Roling

If you own a mid to high-end digital camera, or pretty much any digital SLR, you can shoot in a format other than JPEG. This format is called RAW and offers some significant advantages (as well as a couple of shortcomings) when compared to standard JPEG.

Let's first explain what RAW is. RAW formats capture the raw data from your digital camera's sensor and preserve it in a file for you to manipulate outside of the camera. No adjustments or processing are applied to the image data at all, it's simply a collection of pixel values at the time of exposure.

By comparison, when you take a photo in standard JPEG format, your camera may boost the contrast and saturation, apply some sharpening, adjust for white balance, and then compress your image into the resulting picture file. This processing all takes place in the camera before the file is saved. That means the computer brain of your camera has to make all of these calculations and adjustments before saving the file to your camera's memory.

When using JPEG, your picture has already been processed and compressed once before it reaches you for the first time. On the other hand, RAW formats are more like a traditional film negative. They contain the raw data captured off the sensor, and they need you to "develop" them before they end up as the final picture.

The downsides

Herein lies the major drawback most people encounter when using RAW: You have to post-process the photos before they can be used. Out of the camera, RAW files are not something everyone can view. Only specialized RAW conversion programs, like RawShooter Essentials in Figure A, can natively read them, and the unfortunate thing is that every RAW format for pretty much every camera is different.


Pixmantec's RawShooter Essentials (click for larger image)

There is no standard for RAW, despite the best efforts of Adobe, which will be outlined later in this article. Because every camera vendor's sensor is different, the RAW formats vary widely. RAW files are also much larger than their JPEG counterparts. Since they're not compressed like a JPEG, the file sizes can be two or three times larger. This means you can fit far fewer pictures on your memory card when you shoot in RAW.

Another limitation some people find with RAW is that many cameras won't let you shoot in RAW in the camera's creative or auto modes. For example, many cameras have a sports, portrait or landscape mode that automatically sets up your camera for those conditions. Many cameras can only shoot JPEG under these circumstances. In order to utilize RAW you have to generally shoot in program mode, fully manual, or in aperture or shutter priority.