Raw data is generated when light is received by the photodiodes on a sensor. Depending on the intensity of the light, a stronger or weaker signal is generated. This data is read off and stored as unprocessed data on the memory card.
A RAW file contains more than one set of data. A DSLR file contains calibrated raw data plus the file header. A digital back file contains the actual raw data, calibration data for the digital back files, and the file header information.
The file header is kept separate from the image data in digital back RAW files. The file header contains what is described as metadata (the information recorded by the camera at the time of capture), comprising the following:
- Image Thumbnail (usually a TIFF, but sometimes a JPEG)
- Exposure information
- White Balance (that the image was shot at)
- Contrast curve
- Recorded pixel size
- Camera data (shutter speed/aperture/focal length etc)
More than 100 pieces of data are stored together.
The White Balance determines how the file will look when Capture One creates the preview. The ISO, exposure data, and camera model information are needed to calculate the noise reduction used by Capture One.
Capture One de-mosaics the RAW-file information from the Bayer filter mounted onto the sensor to produce image files with three colors per pixel. This process uses an extremely sophisticated and patented algorithm.
The in-camera ISO and White Balance settings are applied to the image together with the formula developed for Capture One when the preview is created and displayed in the Viewer, in what is called a variant. Once the variant file has been produced, nearly all the variables can be changed (Contrast Curves, Sharpening, and Color Balance).
One of the really big advantages of RAW files is the ability to change the white balance after the image has been captured. This is often not possible with lossy formats like JPEG. The adjustments made to the image in Capture One are applied to the preview and added to the settings file. No changes are made to the raw data at any time.
Once the process button is pressed, raw data is processed using the settings file. At this point, the true pixel-based image is formed and output to specific dimensions.