A Reel Slice Productions

• White balance. The white balance setting on the camera has no effect whatsoever on the captured pixels when you shoot raw—it’s simply recorded as a metadata tag in the raw file. Some raw converters can read this tag and apply it as the default white balance (which the user can then override if desired), while others may ignore it completely and analyse the image to determine white balance.

• Colorimetric interpretation. Each pixel in the raw file records a luminance value for either red, green, or blue. But red, green, and blue are pretty vague terms—if you take a hundred people and ask them to visualize “red,” you’d almost certainly see a hundred different shades of red if you could read their minds. 

Many different filter sets are in use with digital cameras. So the raw converter has to assign the correct, specific colour meanings to the “red,” “green,” and “blue” pixels, usually in a colorimetric ally defined colour space such as CIE XYZ, which is based directly on human colour perception.

• Gamma correction. Digital raw captures have linear gamma (gamma 1.0), a very different tonal response from that of either film or the human eye. So the raw converter applies gamma correction to redistribute the tonal information so that it corresponds more closely to the way our eyes see light and shade. (This property of digital capture has important implications for exposure settings when shooting, which I discuss in a paper called “Raw Capture, Linear Gamma and Exposure”.)

• Noise reduction, anti aliasing, and sharpening. Problems can arise with very small details in an image. If the detail is only captured on a red-sensing pixel or a blue-sensing pixel, the raw converter may have a hard time figuring out what colour that pixel should really be. Simple de mosaicking methods also don’t do a great job of maintaining edge detail, so most raw converters also perform some combination of edge-detection and anti aliasing to avoid colour artefacts, noise reduction, and sharpening.