Sometimes, I like to turn things upside down by asking students to bring in their own images, challenging me to correct them on the fly for the class. The exercise is revealing, because even though I specifically ask for RAW files, at least 50 percent of what I get will be RGB files in TIF or JPEG format. This tells me that there’s still a huge gap in understanding, and I feel pretty strongly that until you really study the controls and practice them on a variety of images (mostly RAW), you’ll never really know how much you’re giving up when starting with JPEG.
My article in the May/June 2014 issue of DPP, "What Is A RAW File?" goes into great detail about how raw image data is stored and should help to explain this slightly difficult concept. In it, we saw how Exposure Values in a scene are compressed into the Lightroom editing space using a process known as tone mapping. Tone mapping compresses the exponentially increasing values of light found in the real world into tonal relationships that we recognize as a photograph. That’s a mouthful, I know, and understanding why tone mapping is necessary is worth the effort. After all, this is what the science of photography is: how you map the giant range of tones out there in the real world into a representative image that you can hang on your wall.
And so, that’s why we want to start with the raw data. The reason you have so much more flexibility when starting with RAW is because you’re shaping it before it’s tone mapped into RGB. Choosing a white balance, setting your white point, black point and basic tonal distribution are all much better when performed on raw data. And that’s what’s absolutely unique about the first eight controls in the Basic panel. These controls are operating on the raw data in its native, linear space.
Take White Balance, for example. White Balance is the set with the first two controls in the Basic panel, and it’s generally the first thing I’ll approach when correcting a photo (Figure 1). When you shoot RAW, you have all the colors of light the camera was able to capture in the original scene, completely unprocessed. So setting a white balance in-camera is entirely unnecessary. When you adjust white balance in RAW, you’re literally scaling the red, green and blue channels separately to create a neutral balance in the linear grayscale data. When you’re shooting JPEG, the camera must assume a white balance for the conversion, and if that assumption is off by much, the resulting color cast will be almost impossible to fix (Figure 2).
The flexibility you have in color correction in RAW is a large part of the benefit. And the flexibility you have in tonal correction using the next six controls are just as great, if not greater.