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Author Topic: Gamma 2.2 vs. L*  (Read 13111 times)

jjlphoto

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Gamma 2.2 vs. L*
« Reply #20 on: January 29, 2009, 11:53:46 AM »

When you say 'quantization' do you mean how quickly the transition from black to white appears? I do notice that when I make a cal/profile at L* and do the greyscale test, (black to white, left to right) the tones tend to bunch up towards the left a bit more than when I make a cal/profile at 2.2
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Czornyj

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Gamma 2.2 vs. L*
« Reply #21 on: January 30, 2009, 04:53:19 AM »

Quote from: jjlphoto
When you say 'quantization' do you mean how quickly the transition from black to white appears? I do notice that when I make a cal/profile at L* and do the greyscale test, (black to white, left to right) the tones tend to bunch up towards the left a bit more than when I make a cal/profile at 2.2

I think Andrew meant, that gamma 1.8 is closer to TRC of CMYK offset print than gamma 2.2, so when you convert gamma 1.8 encoded RGB image to CMYK, you loose less tonal information. It may have some meaning for pre-press operators.

What you observe is right - of course there's a difference between L*, gamma 2.2 and gamma 1.8 calibrated display - each of these is a differnet function of black to white transition, and what you actually saw after calibration is the difference between them. That's what's the reason of small banding, when there's disconnection between TRC of an image, and TRC of a display - when they're the same, Photoshop just displays the RGB numbers of the transitions. When they're different, Photoshop's CMM corrects the RGB numbers of transition, to get the same brightness. To put it in other words - when you look at gamma 2.2 encoded gradient on gamma 2.2 calibrated display, and at L* encoded gradient on L* calibrated display they look different. But when you'll look at gamma 2.2 encoded gradient on L* calibrated display, it will look in the same way as on gamma 2.2 calibrated display (apart from small banding).
« Last Edit: January 30, 2009, 05:54:51 AM by Czornyj »
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