the posterization disappeared if the zoom was closer to 100%.
Images should always be evaluated on screen at 100% magnification.
Images should always be evaluated on screen at 100% magnification.
For many methods I’d agree … but this amount of posterization affects how anyone would evaluate the overall composition. It also affects layered documents only. The link below includes an example of the image in question and also its "copy merged" 16bit equivalent.
<
http://www.michael.shaffer.net/decor/posterization.jpg>
cheerios 🙂
Michael,
I don’t know your excact steps, but I did this:
Took a 16 bit colour image with sky gradient, Used Channel Mixer (Monochrome; 150% Red; -50% Blue) as an Adjustment Layer.
Then I added a Levels Adjustment Layer, Darkened the mid-point.
With all Layers intact I see no posterisation at 25, 50 and 100%, also not merged or flattened.
Does this approximates what you did?
Rob
hello Rob, and thanx for taking a stab at it … but I need admit that a number of layers are in play and the posterization may be a simple effort of PS to reduce refresh computations.
Above the RGB base, there is a curves adj layer, a levels (mode multiply), the channel mixer, and a final adj layer( levels, mode multiply with a gradient mask for the sky).
I think what you’re seeing is just the fact that your display is limited to 8 bits per channel.
In the end, the printed result is the only final way to judge.
I think what you’re seeing is just the fact that your display is limited to 8 bits per channel.
But then we wouldn’t see the difference within his posted example, would we?
Rob
I think what you’re seeing is just the fact that your display is limited to 8 bits per channel.
Rather a strange response from one who is usually right-on, and who apparently hadn’t seen my example in post#2(?)
Still … if I am to take Mr Cox’s response correctly, then what I am seeing is not normal behavior, when I assumed CS2 was simply employing a computational shortcut. That is, I really didn’t expect PS to keep up with many 16bit adjustment layers, more a question of how many could I expect to see an accurate display from?
cheerios 🙂
I think one important concept is not to assume all the time that onscreen representation/degradation of data with actual degradation of data.
I think someone recently posted about how jaggies appear at odd steps (eg 66.6% and 33.3% zoom levels as opposed to 25%, 50% 75%).
While the effect may not be obvious all of the time there are likely to be occasions when funny zoom levels may the data look worse than it really is?
OK, that example doesn’t look normal.
But I’d have to see exactly what adjustments you’re doing to figure out why you’re getting banding.
(and sorry if I’m off my game, I’ve been out sick for a little too long now…)
The posterization you’re seeing is due to 2 things:
1) Photoshop uses pyramid levels for previewing at 50% and below. For a 16 bit document, those pyramid levels are only 8 bits/channel (because it’s just a preview). Adjustment layers will apply to the pyramid levels for your preview.
2) You applied several _extreme_ adjustments to make those clouds visible. If you had done this to an 8 bit image, you would get results similar to what you see below 50% zoom.