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ADV7181D : Color Space Conversion Matrix

Question asked by Milwaukee on Aug 16, 2013
Latest reply on Jan 8, 2014 by spirov

Hello,

 

My situation:                                  

I'm working with the ADV7181D.

I am supplying it with PAL RGB(3 channel) video, and I have the device configured properly so that it is successfully sync'ed to video.

I am able to detect the sav and eav tags in the output video stream, and they behave as expected.

My configuration is set so that I am using the "SDP" processor with the "Video out 20-Bit" format, in the 4:2:2 mode.

Additionally, I have the device set for "Automatic configuration of the CSC for SCART support",

This is done by setting I2C bit "FB_CSC_MAN", Address 0xEE, bit 7, to the value of "0".

 

I therefore expect the ADV7181D to convert PAL, 3-channel RGB video to a 20-Bit 4:2:2 YCrCb video stream.

 

My goal:                                       

My job is to reconvert the YCrCb stream from the ADV7181D back to RGB (I use an FPGA and code the YCrCb-to-RGB matrix myself).

My conversion back to RGB uses the following color space conversion matrix (also known as "ITU-R BT.601", and "YCrCb to RGB color conversion for SDTV").

 

     Red    = 1.164(Y-16) + 1.596(Cr-128)

     Green = 1.164(Y-16) - 0.813(Cr-128) - 0.392(Cb-128)

     Blue    = 1.164(Y-16)                          + 2.017(Cb-128)

 

My problem:                             

I suspect that the color conversion matrix inside the ADV7181D uses different RGB-to-YCrCb coefficients.

My matrix therefore does not accurately convert the video back to the original RGB values.

I suspect this because green input video has an unexpectely large influence on the Y value streamed out of the ADV7181D.

When I remove green from the video source (but keep the syncs, and red and blue video channels), the Y channel falls to a value below 25% max value (even with the red and blue input video channels at maximum amplitude).

This behavior is not in accordance with the RGB-toYCrCb matrix I am assuming is in place in the ADV7181D.

 

My question:                             

What color space conversion matrix does the ADV7181D use to convert RGB to YCrCb?

If possible, please provide the actual coefficients (or the matrix) used by the device.

 

Kind Regards

Jeff

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