What is Raw Mode?
Raw mode is a special image recording option that is available on digital SLRs, Compact System Cameras, and other high-quality digital cameras. If your camera has this option, you have access to much higher image quality than the standard JPEG file format.
Essentially, Raw mode is just what it sounds like. It’s the raw data straight from the camera’s sensor. In a digital camera the photographic image is, as I’m sure you’re aware, captured by an electronic image sensor. This sensor has millions of tiny photocells that produce a charge when they are exposed to light; the brighter the light, the higher the charge. Digital camera sensors don’t record the colour of the light hitting them, just the brightness, so a special mosaic of coloured filters is placed in front of the sensor, called a Bayer filter.
Naturally, the image generated by the sensor and filter wouldn’t make much sense to the unaided eye, so the signal from the sensor feeds into the camera’s image processor, a combination of computer electronics and software which turns the brightness data from the sensor, adjusted for the colours in the Bayer filter, into a full colour digital image that you can view and print.
Part of that process includes reducing the bit-depth of the basic image data (the amount of 1s and 0s used by a computer to describe each pixel), usually from 36-bit (12 bits per channel) or even 48-bit (16 bits per channel) to 24-bit (8 bits per channel), which makes a smaller and more easily processed file, but loses some colour depth because of the smaller palette that can be represented by that many bits. Other adjustments to the colour balance, such as unusual white balance settings, can also reduce image quality, as will heavy noise reduction.
In order to save space on the memory card, produce faster transfers and make it easier to display and print the photograph on a computer, the image is usually converted to a compressed JPEG file. Unfortunately JPEG compression also reduces the image quality, and can introduce artefacts into some areas of the image.
The main advantage of Raw shooting, apart from the improvement in overall image quality, is that it bypasses the in-camera image processing, such as white balance, saturation, sharpness etc. This sounds illogical, but it’s not really. The processing that takes place in the camera is pre-set before the shot is taken, and irreversible once the image has been converted to a JPEG file. By shooting in Raw mode, you can make the processing adjustments after the shot has been taken, and if you need to change them you can do so as long as you have the original Raw file.
The downside to Raw file recording is of course that the saved files are much larger, so they take a lot longer to save to the memory card, and you can fit fewer of them on there. For a typical 16MP DSLR, a high quality JPEG file will be around 8MB, while a Raw file will be around 25MB, over three times the size.
Many of the more recent DSLRs have the ability to record Raw and JPEG image files simultaneously. This has the advantage of the convenience of JPEG with the versatility and quality of Raw, but takes up even more space on your memory card. Fortunately the price of very large memory cards is falling almost daily, so this needn’t be much of a problem.
Modern cameras all come supplied with Raw processing software, although if you have Photoshop, it has Adobe Camera Raw built in as part of the application. Try to get used to always shooting in Raw mode on your camera. The quality and processing possibilities are much greater than JPEG files. These days, even some camera phones have the ability to shoot in Raw format. They are larger file sizes than JPEGs but the benefits become clear once you start to understand how much more processing ability you have. Your photos will see a marked improvement when you use Raw.