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Author Topic: RGB to XYZ conversion problem (bug or not?)  (Read 2480 times)

Floating Point

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RGB to XYZ conversion problem (bug or not?)
« on: August 10, 2015, 11:41:38 AM »
I have RGB images as input (detail in attach: image1.jpg) - the same thing happens whatever filetype I use (TIF, DPX...). Those images are converted to XYZ colorspace using OpenDCP. I use EasyDCP to play the DCP produced using those JPEG2000 files and I get a strange output, part of which is shown in attach: image2.jpg.

By just looking at those two images, they seem identical (I think I have managed to reach my workflow to satisfy correct color profiles etc.), but when you decompose the screenshot of image2 (as opposed to decomposing of image1) to R, G and B channels, you can see that they aren't single-color fills anymore, - there is a lot of some noise present. I understand what is going on when you don't get the exact color because of some color profile issues but I don't understand what could have happened to get a very random oscillating fill instead of expected uniform fill (whatever color happens in the output).

This type of output also happens when I play the resulting MXF file using djv_view and those irregularities are also visible when viewing j2c images without colorspace conversion.
If that can be of help, it seems this problem is not visible when reproducing in NeoDCP but I suppose that could be because of some interpolation done by that piece of software.

Jiri Mlynarik

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Re: RGB to XYZ conversion problem (bug or not?)
« Reply #1 on: August 11, 2015, 07:02:37 AM »
The JPEG2000 compression algorithm is not an ideal choice for synthetic images as it may create more-or-less visible compression artifacts such as the one you've attached here.
I assume you've been viewing the J2C images directly in the sRGB color space, without performing the XYZ to sRGB color space conversion. Remember that in this case the J2C images' gamma and your display device's gamma don't match and thus the compression artifacts may be heavily pronounced.

My experience with NeoDCP player shows that it has very accurate color rendition and its picture quality is also top notch. I believe the problem you are facing is probably only gamma-related, and you should rather trust the NeoDCP player. Set your monitor to the sRGB color space and configure the player to use the default XYZ to sRGB with 2.2 gamma color space conversion. Or alternatively, create an ICC profile for your monitor and import it to NeoDCP player, and you should be 100% safe.

Jiri

dcinemaforum.com

Re: RGB to XYZ conversion problem (bug or not?)
« Reply #1 on: August 11, 2015, 07:02:37 AM »