Color issue with ADV7171

Hello people,

I am currently working with the ADV7171 video encoder, and until now I was managing to make it work for my needs, that was only monochrome images.

The problem is that now I need to make a color map to this image, and show it coloured. But when I turn on the register bits Color Enable (MR24 = '0') and Burst Enable (MR25 = '0'), the colors appear, but when I have small objects (lines) in the image, like letters, I get a strange behaviour. The image shows the difference between the same image with and without color.

The coloured image is a lot more grainy, noisy. It seems that this noise is different for some frames, but it is repeated each n frames (or fields). Maybe the odd field is "different" from the even field, then this causes this problem. I attached one video that shows this.

I think the subcarrier frequency configuration is OK. I am using Square pixel NTSC. So, my pixel clock is 24,5454MHz and the ScFR registers are x"25555555".

I tried to fine tune this frequency, but I couldn't.

Please, if someone knows anything that could cause this problem, I would appreciate any help.

Thanks very much.


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