Film-Tech Forum ARCHIVE: Raster Test / What it means?

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Posted by Lucas Iaccarino (Member # 8762) on 02-19-2016, 11:46 AM:

Hello, i´m testing a Cinema Complex for a Film Festival and I have found some difference between the Screens when I played the Raster Test (Horizontals and Vertical Lines Projection).
Can someone explain me what this test means? I have two Screens with Bold Lines and other two that presents a big black Blot at the center of the horizontal lines.
Its about lens resolution? Focus?
The projector are Christie 2230 and Barco DP2K 23B
Thanks

Posted by Carsten Kurz (Member # 5396) on 02-19-2016, 12:59 PM:

I'm not sure if I understand what you're after, which raster test do you mean, where do you find them, is it DCPs, or internal test images? When you see non-linearities from perfect 1:1 raster file, it usually points towards some sort of scaling. Early DCI projector software was only able to process a 1:1 pixel relationship and a 1:1 pixel raster should display as such. But now, the ICPs support scaling, and with regular test patterns, this can reveal scaling artifacts.

- Carsten

Posted by Dave Macaulay (Member # 813) on 02-19-2016, 03:37 PM:

I expect this place has Christie projectors with non-motorized lenses, and the installer has used scaling to accomplish flat/scope image alignment. A manual lens can't accommodate anything except rather unusual screen and masking setups without adjustments ... or scaling.
IMO using scaling is a terrible practice but it saves needing someone to adjust the lens zoom and position to change from flat to scope.
Image scaling is not supposed to be used for digital cinema. There are always artifacts, I think you're seeing them.

Posted by Lucas Iaccarino (Member # 8762) on 02-22-2016, 11:12 AM:

I really believe is that.
I will check it as soon as posible.