how to convert RGB to YIQ color space ?

hello sir, I am trying to convert an RGB image to YIQ color space, and convert it back to RGB. what is the correct way of converting into YUV color space to get Y I and Q component separately.

Answer 1

[Thorsten]

Hi Namita, there is a function on File Exchange that does a lot of color conversions that might be useful for you

http://www.mathworks.com/matlabcentral/fileexchange/28790-colorspace-transformations

Answer 2

[DGM]

Image Processing Toolbox has rgb2ntsc() and ntsc2rgb() which do YIQ conversion without the need for anything external.

https://www.mathworks.com/help/images/ref/rgb2ntsc.html

https://www.mathworks.com/help/images/ref/ntsc2rgb.html

EDIT: rereading this, I noticed something I glossed over before.

what is the correct way of converting into YUV color space to get Y I and Q component separately.

Everyone seems to refer to all luma-chroma transformations using a random assortment of names as if they're all identical. That said, the question could be taken literally and it would be answerable despite YUV and YIQ not being completely interchangeable synonyms.

The two are simply related by a 33 degree rotation. You could convert into YUV and then calculate I and Q from UV:

rgbpict = imread('peppers.png');

% forward xform from RGB to BT601 YUV
A = [0.299 0.587 0.114; -0.14713 -0.28886 0.436; 0.615 -0.51499 -0.10001];
yuvpict = imapplymatrix(A,im2double(rgbpict));

% rotate chroma components from YUV to YIQ
[Y U V] = imsplit(yuvpict);
I = -sind(33)*U + cosd(33)*V;
Q = cosd(33)*U + sind(33)*V;
yiqpict = cat(3,Y,I,Q); % reassemble into a single array if desired

... or you could simply apply the rotation to A prior to conversion instead of to the entire image after conversion.

rgbpict = imread('peppers.png');

% rotate A instead of the entire YUV image
A = [0.299 0.587 0.114; -0.14713 -0.28886 0.436; 0.615 -0.51499 -0.10001]; % for RGB->YUV
R = [1 0 0; 0 -sind(33) cosd(33); 0 cosd(33) sind(33)]; % rotation 
A = R*A % for RGB->YIQ

yiqpict = imapplymatrix(A,im2double(rgbpict)); % convert straight to YIQ

... but if you looked up the transformation matrix for YUV, you could have just looked up the one for YIQ instead.

rgbpict = imread('peppers.png');

% why not?
A = [0.299 0.587 0.114; 0.5959 -0.2746 -0.3213; 0.2115 -0.5227 0.3112];

yiqpict = imapplymatrix(A,im2double(rgbpict)); % convert straight to YIQ

... but remembering those matrices is a pain, so maybe just

rgbpict = imread('peppers.png');

yiqpict = rgb2ntsc(rgbpict); % convert straight to YIQ