Chroma Transients

Colour looks great when there are 4 or more horizontally-adjacent pixels. But when there is an isolated single overlay pixel in a scanline (e.g. as part of a vertical line or the upright stems of text characters) then the colour is faint, as you can see in this image below.

Altimeter pointer

Notice how much darker the vertical and diagonal lines are compared to the solid green horizontal lines. Also, although it’s not visible here, the green appears to “bleed” into the adjacent left and right pixels from the video feed.

This may be the result of signal processing in either the decoder, encoder, or my video monitor. Or it could be the result of the analog video encoding, which attempts to squeeze 3 signals (1 luminance and 2 chrominance) down one wire, with limited bandwidth. The ADV7184 datasheet states:

Due to the higher bandwidth, the signal transition of the luma component is usually much sharper than that of the chroma component. The color edge is not sharp and can be blurred, in the worst case, over several pixels.

The decoder has a Chroma Transient Improvement block, and the encoder has various Digital Noise Reduction filters. I will need to experiment with all of them. Next step will be to add a pushbutton handler which will progressively enable and disable the CTI and DNR settings so I can observe what difference if any they make.

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