This is a great article highlighting the skills of the technicians who worked on some of the most famous photographs ever taken. You can see the annotations made on the test prints of the images telling the technician how long to burn-in or dodge certain parts of the image so that the photographer can get the tonal effect he/she wants on the photograph.
This is very similar to the contrast grading process I use when working on my black and white prints in that I envisage how much i need to burn or dodge parts of the image. On particularly difficult images, I have even duplicated the photo layer in Photoshop and marked up section on the image and how I would like them to appear.
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