Master your DSLR: in-camera processing
WHAT OPTIONS ARE AVAILABLE FOR ADJUSTING THE LOOK OF YOUR PHOTOS?
QUITE A LOT of things happen very quickly when you press the shutter release button on your camera. The light reflected off the subject is captured by the lens and fed to the image sensor, where it’s recorded as an analogue electrical signal then turned into digital data by the analogue/digital converter.
All of this typically happens in a fraction of a second, but it’s really just the start of the process of creating an image. Before the file ends up being temporarily stored in the camera’s buffer prior to being written to the memory card, the massive amount of data created for each image you shoot has to be crunched. Digital processing that’s carried out at this stage includes adjustment of the white balance, colours and contrast, along with lens corrections, noise reduction and sharpening. How — or rather when — these adjustments are applied depends on the file format selected on the camera. In the case of JPEGs or TIFFs, they’re applied to the image before it’s finally compressed to create a smaller file size (in the case of a JPEG) and saved to the memory card. If you’re recording images as raw files, the processing data is saved as part of the file but not applied.
TO CONVERT THIS INFORMATION INTO A VIEWABLE IMAGE FORMAT SUCH AS A JPEG, THE RAW DATA FIRST NEEDS TO BE DECODED. THIS IS NORMALLY DONE USING RAW PROCESSING SOFTWARE ON A COMPUTER, BUT SOME CAMERAS ENABLE YOU TO CONVERT A RAW FILE STORED ON THE MEMORY CARD TOO.
At this stage, a raw file is not an image at all: rather a data file that contains the raw binary code from the camera’s image sensor. To convert this info into a viewable image format such as a JPEG, the raw data first needs to be decoded. This is normally done using raw processing software on a computer, but some cameras enable you to convert a raw file stored on the memory card too. All images start out as raw image data; it’s just that, in the case of a JPEG or a TIFF, the camera automatically carries out the image adjustments for you.
So why would you bother altering settings like white balance and sharpness in the camera when raw files let you do it later in the comfort of your own home?
Well, for a start, you’ll probably want a more accurate preview of the image. The image you see displayed on the rear screen of a DSLR during playback and Live View, and in the viewfinder of a camera equipped with an electronic viewfinder, is actually a JPEG preview that’s based on the image processing settings made on the camera.
This is the case even if you shoot raw, although the file that ultimately ends up on the memory card still contains all that raw sensor information.
This JPEG preview is a useful creative tool. For instance, you can get a feel for how an image will stack up in black and white, while still recording the colour data in the raw file that can be used for a more sophisticated mono conversion later.
There are also technical considerations: the exposure histogram you see on the camera’s screen is based on the JPEG preview, and will reflect any changes you make to the picture style or white balance. You’re unlikely to get an accurate reflection of the raw file if you have a devil-may-care approach to in-camera image processing.