[solved] Resize causing color change

board123 · 23rd December 2009, 22:15

I've been using the built in resizers (generally Lanczos and Spline) for a long, long time and only noticed this issue today. I think the pictures will speak for themselves. I've resized the screenshots with Photoshop to make them more web friendly. The only things of interest here are the colors.

Original h264 source

Re-encoded with x264-1376 and LanczosResize

The easiest areas to spot the color change are the green chair in the background, the flowers in the hair and the cell phone. Skin tone also changes slightly. It seems the reds and greens are exaggerated while blues are subdued. I've done a lot of tweaking and confirmed that it is definitely the resize filter that's causing this.

Am I the only one having this problem? I haven't found any similar issues on the web regarding resize filters. This is such an odd problem...

bizz & buzz · 24th December 2009, 01:45

If you are downscaling from HD to SD, perhaps using ColorMatrix will fix this issue.

EDIT: here is a very good summery on why,when and how to use ColorMatrix:
http://forum.doom9.org/showthread.php?t=133982

IanB · 24th December 2009, 02:50

My guess is you have a Rec601/709 translation in your process.

Taking your original PNG plus ConvertToYV12(Matrix="Rec709") comparing to your encoded PNG plus ConvertToYV12(Matrix="Rec601") and they match

board123 · 24th December 2009, 07:35

After some more playing around before your replies, I reached the same conclusion. It is indeed a case of the output being treated as Rec601.

ColorMatrix(mode="Rec.709->Rec.601") in the script fixed the problem. Thanks.

23rd December 2009, 22:15	#1 \| Link
board123 Banned Join Date: Jan 2007 Posts: 19	[solved] Resize causing color change I've been using the built in resizers (generally Lanczos and Spline) for a long, long time and only noticed this issue today. I think the pictures will speak for themselves. I've resized the screenshots with Photoshop to make them more web friendly. The only things of interest here are the colors. Original h264 source Re-encoded with x264-1376 and LanczosResize The easiest areas to spot the color change are the green chair in the background, the flowers in the hair and the cell phone. Skin tone also changes slightly. It seems the reds and greens are exaggerated while blues are subdued. I've done a lot of tweaking and confirmed that it is definitely the resize filter that's causing this. Am I the only one having this problem? I haven't found any similar issues on the web regarding resize filters. This is such an odd problem... Last edited by board123; 24th December 2009 at 07:46.

24th December 2009, 01:45	#2 \| Link
bizz & buzz Banned Join Date: Jun 2008 Posts: 94	If you are downscaling from HD to SD, perhaps using ColorMatrix will fix this issue. EDIT: here is a very good summery on why,when and how to use ColorMatrix: http://forum.doom9.org/showthread.php?t=133982 Last edited by bizz & buzz; 24th December 2009 at 01:52.

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24th December 2009, 02:50	#3 \| Link
IanB Avisynth Developer Join Date: Jan 2003 Location: Melbourne, Australia Posts: 3,167	My guess is you have a Rec601/709 translation in your process. Taking your original PNG plus ConvertToYV12(Matrix="Rec709") comparing to your encoded PNG plus ConvertToYV12(Matrix="Rec601") and they match

24th December 2009, 07:35	#4 \| Link
board123 Banned Join Date: Jan 2007 Posts: 19	After some more playing around before your replies, I reached the same conclusion. It is indeed a case of the output being treated as Rec601. ColorMatrix(mode="Rec.709->Rec.601") in the script fixed the problem. Thanks.