Gamma of Primaries

[Anonymous]

Do I have this right and a question.

It seems to me that if the gamma of each of the three primaries is not accurate then achieving accurate secondary’s will be very difficult. Conversely, if the gamma for the three primaries is dead on then the secondary’s should also be spot on without further adjustment needed. Not so?

Then for how devices actually work, when you change the overall gamma do the three primary gamma’s automatically change appropriately or is it necessary to change all four, RGB and total?

John
THX

Topic

[Gregg Loewen]

hi John

A good question for Dr Rudd too….Id love to have his input.

Basically when asking about the “intensity” of the primaries at a variety of stimulus points you are correctly talking about primary gamma (vs gray scale gamma).

A good test for color decoding is measuring primary intensity at 100% stimulus then comparing it to primary intensity at 75% stimulus. If it is not in the same proportions then there is a color decoder error (which may or may not be further correctable). This is essentially measuring primary gamma response (in the color decoder).

We teach to do CMS adjustments at 75% stimulus as this is closer to the percentage of stimulus of an APL (average picture level), and thus best represents an average picture.

Hope this helped ??

Gregg

[Author]

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