DVD Video Test---Chroma

[gpibssx]

I am using Image Card and Labview& Vison *Vison builder to devlop the video test from DVD PAL output. Now i have a question. Pls see the attachment.I am analyzing the Chroma. I want to canculate the components of R,G,B in the chroma picture, That means i want to get the coordiates for the turning point in the Red color profile,Green color profile,Blue color profile.Also i want to get the max Y value for the RGB color. But i cann't find the VI to canculate the turning point? Could u give me some suggestion? Example best!!

[BruceAmmons]

It looks like the simplest thing to do is split each line profile in half, and fit a straight line through each half. All the points you are looking for could be found by locating the intersection between the two lines or their min/max values at certain points.

Bruce

[gpibssx]

could u give some source code as the example??

[BruceAmmons]

I don't have time to write your code for you, but I can explain a little more.

From your line profile, you should be able to generate a series of X and Y values. X is position and Y is intensity. Split this array in half, and use curve fitting to generate a straight line through the points. A min-max fit would actually be better than a least squares, but that is more difficult to program. Once you have an equation for each half, you should be able to solve for the intersection point and also evaluate each endpoint.

Another interesting way to do it would be to use non-linear Lev-Mar fitting. You could write an equation that has four unknowns - the Y coordinates at the beginning and end, and the X and Y coordinates in the middle. You c
ould supply some good guesses to begin with, and it would iterate until the best fit was found. Take a look at the Lev-Mar vi supplied with LabVIEW. It would also give you a good idea of how much deviation there is from the straight line fit.

Bruce