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Shades of gray: my display's limitation or a Bits-per-channel issue?

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Alan LangdonShades of gray: my display's limitation or a Bits-per-channel issue?
by on Sep 21, 2012 at 2:29:07 am

I am making in AE CS4 the end titles/credits for a short film which will be transferred to 35mm film.
The transfer house requested that I send the end credits as a TIF sequence with Alpha channel.

The titles sort of wipe on from left to right, as if coming through a fog, and together with them I have a layer of "fog" that fades on and off around the text, as if the text were sort of smoking/dissipating. The effect was created using the common Fractal Noise effect and some masking to shape the "fog/smoke" around the text only, as opposed to filling the screen, which is otherwise 0,0,0 black in value. The mask has considerable feathering of course, to make the fog gradually come out of black.
(see attached image:)


The project is set to 32 bpc, with NO working space being used, and also without the "Blend Colors using teh 1.0 gamma" option. Why? Because I have never fiddled with these and figure best not to now, although I could be missing out on something. In fact, shouldn't the transfer house be requesting specifics on these: bits per channel, color working space, etc?

So, my issue is: when I look at the composition at full resolution/best quality on either of my LG 1920x1080 LED monitors (not professional grade displays, but rather a poor-man's two-screen setup), when I look at the fog/smoke effect surrounding the text, I can see where it starts, as if there were not feathered enough.. The shades of gray, which should be almost invisible to see shifting as they get lighter towards the text, seem to change abrupty from one to the other, incrementing in visible steps which don't look natural. It is as if the composition (or more likely, the display) doesn't have enough color space to show the full gradation. When I tweak the Exposure value in the Composition View, It seems that it might just be monitor that can't handle the varied shades of gray. When I export a Photoshop frame and open it in PS, even there it looks better and the gradations seem more subtle.

So I am very much inclined to think this is a matter of AE's output to my cheap monitor (I am not even full-framing, just using the second display to view the composition panel). If this is the case, can I then rest assured that the TIF sequence they will receive for transferring to film will have enough information to generate smooth, subtle gradations of gray?


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Matthew WoodsRe: Shades of gray: my display's limitation or a Bits-per-channel issue?
by on Sep 21, 2012 at 1:34:34 pm

You are most likely correct. Most LCD monitors, especially cheap ones don't support very many shades of grey. I actually like looking at my video on a cheap monitor sometimes so that I can be aware of this, and fix it so that no one else sees it. One technique I use to get a feathered edge that will look good on any display is to use AE's "ramp" effect on a solid, then set that to a luma matte for the layer I want to feather. The nice thing about the ramp effect is that it has a "scatter" feature which you can crank up a bit to dither the gradient, and hide the banding. Its a less controllable than a mask, but it should make your banding disappear. Actually a "scatter" option would be a great feature request for the built in masks. I have never thought about requesting that.

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Alan LangdonRe: Shades of gray: my display's limitation or a Bits-per-channel issue?
by on Sep 21, 2012 at 3:19:05 pm

Thanks for the info, very helpful. WHiel reseraching for this topic, I dug into Color Management, somehting I never even thought about, I always just used 16 or 32 bpc. So now I am learning about linear light (gamma 1.0), as well as Color Space workflow. And it looks like the 35mm transfer house which will join the Apple Pro Res HQ footage with my TIF sequence will need to provide me with the proper COlor Space they want the TIFs to be in, so compositing works fine.



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Walter SoykaRe: Shades of gray: my display's limitation or a Bits-per-channel issue?
by on Sep 21, 2012 at 5:47:32 pm

[Alan Langdon] "So I am very much inclined to think this is a matter of AE's output to my cheap monitor (I am not even full-framing, just using the second display to view the composition panel). If this is the case, can I then rest assured that the TIF sequence they will receive for transferring to film will have enough information to generate smooth, subtle gradations of gray?"

You can quickly verify the smoothness of a ramp by moving the mouse over the image and keeping an eye on the Info panel, which will show you an RGB readout of the color value under the cursor. If you see those numbers moving even in an area of flat color on your screen, you know the additional data is there and that your screen just cannot display it properly. If you see steps in the values that coincide with the steps on-screen, verify that you don't have any 8bpc effects anywhere that may be truncating the depth.

Also, when rendering, make sure the bit depth in the output module is set to Trillions of Colors -- this is equivalent to 16bpc. You don't want to work in all that depth only to dither it down to 8bpc by outputting at Millions of Colors.

TIFF also supports floating point, but you should check with your post house to make sure you're delivering something they can use.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
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