The processing steps are done for both the preview scan and the full scan.
The first step is using the infrared data to do a first attempt at dust removal (if enabled). This reads the whole image once to characterize the relationship between the color channels and the infrared channel. Then it reads each line once, correcting it for dust spots, marks each dust spot that's severe, and passes each line to the subsequent steps for further processing.
The next step is applying the cleaning filter. This filter tries to remove dust spots by using the infrared data to identify and remove dust spots.
The next step is performing corrections for film media. This reads the whole image once to compute the intensity of the film base, and then reads each line, corrects it based on film characteristics, and passes each line to the subsequent steps for further processing.
Next, an optional image size reduction is done. The "Options|Size reduction" option is used to reduce the size of an image by averaging blocks of pixels. Multiple lines are processed and then single lines are passed to subsequent steps for further processing.
The next step is color correction. The whole image is read once, and the options from the Color tab are used to convert to the final colors of the output images. The inputs to this step are 16-bit linear light samples, and the outputs from this step are gamma corrected samples.
The last step is sharpening. A simple 3x3 filter is used to increase the sharpness of the image.
Once the image data has been corrected, the image data is saved for display in either the Preview or Scan tab, and is optionally written to a .tif file, a .jpg file, or an index file.