What’s important:

Unlike non-“light”-related aspects (“forms and shapes)”—

— which can only be changed in very limited ways after a photo is recorded—

— “light”-related aspects not only can but sometimes must undergo significant changes after a photo is recorded in order for the photo to qualify as TTG.

Why are “light”-related aspects treated differently than non-“light”-related aspects?

What are “light”-related aspects?

Every depiction in every photograph is either “light”-related or non-“light”-related (most depictions of things in photographs contain both aspects).

The two aspects behave very differently from each other — with numerous implications regarding “viewer trust.”

“Light”-related aspects of photographs (addressed by #10 of TTG’s Allowable Changes, as linked to P2) — sometimes called “tones and colors” on this website — include the general categories of

• brightness
• contrast
• hue
• saturation

What else is covered

Numerous related specific subcategories, tools, and actions are covered by the term “light-related changes” (again, it’s #10 in the Allowable Changes list), such as

• converting a film negative to a positive
• converting a color photo to black-and-white
• burning
• dodging
• highlight detail
• shadow detail
• curves
• levels
• white balance
• color balance
• tonal relationships in monochrome (black-and-white) photographs
• various other light-related items (including most of the options on the Image > Adjustments menu in Photoshop and their corollaries in similar programs).