AnsweredAssumed Answered

ADV7181D : Color Space Conversion Matrix

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



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