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 either the sharpening filter or cleaning filter. The sharpening filter is a simple 3x3 filter, while the cleaning filters are used to try to remove dust spots. Each line is read once, filtered, and passed to the subsequent steps for further processing.
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 last 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.
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.