# How could I interpret these-2 YUV modulated picture given in wikipedia? is it correct simulation? or something I'm missing?

While reading the wikipedia article on YUV color modulation (which is used in PAL color tv receivers); I visited this diagram:

(and according to the image description there; i.e.

"An image along with its Y′, U, and V components respectively";

the 3rd one is U-component and 4th one is the V-component of the 1st image. Well.

But there; the component U has been described as

U = approx 0.492 (B - Y') ... (where Y is Luma).

So, if the 3rd image show only U; i.e. 0.492 (B - Y') or 0.492 X (Blue-(0.299R+ 0.587G + 0.114B)) ; then in the ultimate result; there would be equal visual reduction in R and G; and B would be the most prominent.

(As well; they've provided a formula too;
U= -0.147R -0.289G +0.436B ; that shows a positive value for only blue, and a negative values of both R and G)

If someone try to simulate it as visible picture; the picture would contain only-blue (which is non-negative).

But surprisingly, in image 3, there is high portion of green too ; i.e. green is behaving in similar, positive way) ; though there I could not find any trace of red component with ms-paint Eyedropper tool. (My eyedropper samples on downloaded original-file ranges from R=0, G=83, B=172 to R=0, G=191, B= 64; and in all samples R=0; on Paint's 255 scale)

So; my question is; is it a wrong picture of U component?

Even if I consider they made a negative copy of U (i.e. gave a -U); still we would obtain Red and Green together as positive; and blue as negative.

U= -0.147R -0.289G +0.436B

= > -U = +0.147R +0.289G -0.436B

But the image shows G and B; not R and G.

In the same way; the 4 th image (V or approx. 0.877(R-Y')) also seems to me showing anomaly from the definitions.

V= +0.615R -0.515G -0.100B

So the positive image would only Red color. But similar to 3rd image; it show proportions of Red and Green; not Red-only. (ms-paint eyedropper samples from original image shown R=147, G=81, B=0 to R=102, G=153, B=0; and in all sampled dots B=0)

If it was a negative copy of V-component; Then we should get positive values of G and B. Not R and G.

So; if these 2 images are correct examples of U and V; what thing I missing about the concept of U and V? what is the basis behind that "extra green" in both the image 3 and 4?

in simple words;

If from a blue image (Component B) if I snatch away a colorless component (Y') then how I get a blue-green picture and not an only-blue picture? or why not blue red?

And same way, if I snatch away a colorless component (Y') from a Red image (Component R); then how I can obtain a Red-Green image and not a only-Red image? or why not blue-red?

• The U and V images should have been displayed in monochrome, just as the Y image was. If a coloured image is a 'vector' containing R, G and B components, then Y, U and V are scalars, they do not have and are not representable as coloured images. – Neil_UK Dec 24 '16 at 14:53
• @user:16880 (David) inviting you to visit this question. – Always Confused Dec 24 '16 at 18:25