Instant Preview mode is the special processing mode that lets generate result in real time. Instant Preview mode is accessible from the Partial Processing Dialog.
To open Partial Image processing dialog, click the toolbar icon or press Alt + R.
Now select the area using the handles in the corners of the image preview, tick Instant preview box and click Instant Preview button.
Tip: Since image processing may take a lot of memory, it’s advisable that you selected small areas. Then the preview will be generated almost instantly providing for excellent distraction-free colorization process.