Using ADV7184 SCART Overlay with ADV7341, isolated pixels are faint

Hi,

I am using the ADV7184 back to back with an ADV7341, to add an RGB overlay over CVBS. I find that when pixels are isolated, with no adjacent pixels in the same line, they are considerably dimmer. This means that vertical lines appear dark and text is of inconsistent brightness.

I thought this may be the the encoder attempting to filter noise, so I experimented with various DNR gain levels and filters but I did not notice a difference.

Here is an example, note how the vertical and diagonal lines in the image are much darker than the horizontal lines.

Vertical and horizontal lines

Is there some way to avoid or mitigate this effect, and have all overlay pixels of the same brightness?

Thanks!

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  • Hi Peter,

    I am not the 100% best expert at the ADV7184 however I might be able to help.

    The FB switching is implemented after any of the SDP filtering so changing the filtering should not have any effects.

    Q1) What is the output format (RGB or YCbCr 422)?  8-bit or 24-bit?

    Q2) What does the image look like if you used a 4 pixel wide overlay instead of just one pixel wide overlay?

    One pixel wide images will have problems in CVBS due to interlacing and the compression with the 422 format.

    From the previous discussions I am beginning to wonder if this problem is related to the ADV7341 filtering a YCbCr 422 signal versus clean RGB output. 

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