How Raw Profiles Work

There are several factors influencing the way colors are registered in a camera. And there are many ways to transform the raw information to RGB.

Colors in a scene are affected by the light illuminating the scene.The sun has a smooth spectral distribution of light and is one of the most favorable light sources when color quality is important. Fluorescent light and most LED lamps are much more difficult.

In order to correctly register colors in a camera, most sensors use red, green and blue filters in a Bayer pattern on the sensor. These filters splits the light in three components, much like our human eyes does. 50% of the pixels on the sensor register green, 25% blue and 25% red components. Each pixel measures the level one single component. All pixels collects photons and converts them into electrons that is converted into a level of voltage. Finally the voltage is sent to an A/D-converter and converted to a binary code representing the voltage level. This is the raw linear image information. The quality of this binary (digital) color information is depending on several factors:
1) The quality of the illumination of the scene.
2) The quality of the filters on the sensor.
3) The quality of the electronic components in the camera.
4) In-camera software handling of the information.

Despite all limitations, raw is the "lowest", least "destroyed" and most complete, level of image color information available from a camera. When transformation from raw to RGB (tiff or jpeg) is performed, image information is truncated. Examples of redundant information are information about color temperatures other than the chosen and additional high-light and shadow details.




There is always a profile involved in this step. The profile "decides" how the color transformation is performed. When using Adobe softwares (Photoshop, Lightroom, Elements or Bridge) most photographers rely on the Adobe standard profile. The most basic type of transform is the "matrix" transform, which works just like the "color mixer" in Photoshop. In addition to this, most camera color profiles contain a more fine-grained correction tool, the "LUT" or "LookUp Table" correction.

Custom raw transformation profiles generated with QPcard 202 or 203 and QPcalibration replaces the Adobe standard profile. The raw information about color values of the reference targets 202 and 203 is registered. By doing so, information of how the scene illumination and camera specifics influence colors is taken into account.

With QPcard 202 or 203 color cards and QPcalibration software you can instantly create custom profiles for almost all advanced cameras and in different light. The main quality of custom profiles is compensation for deviation in hue. Too strong saturation, resulting in "flat" color areas lucking image details, are also taken care of.

With QPcalibration software extension "Adjust", you can manually influence the way colors are rendered by the profile. With three levers, hue, saturation and lightness can be adjusted in 12 sections of the color circle.