Function to convert YCbCr to RGB?

Question

I have Y, Cb and Cr values, each with a size of 8 bits. What would be a simple C function which can convert these values to R,G,B (each with a size of 8 bits)?

Here is a prototype of the function I am looking for:

void convertYCbCrToRGB(
    unsigned char Y,
    unsigned char cg,
    unsigned char cb,
    unsigned char &r,
    unsigned char &g,
    unsigned char &b);

P.S. I am looking for the correct conversion formula only, since I have found different versions of it everywhere. I am very well-versed in C/C++.

SunnyShah · Answer 1 · 2010-10-28T12:26:44.840

14

Here is my solution to my question.
This one is Full Range YCbCr to RGB conversion routine.

Color GetColorFromYCbCr(int y, int cb, int cr, int a)
{
 double Y = (double) y;
 double Cb = (double) cb;
 double Cr = (double) cr;

 int r = (int) (Y + 1.40200 * (Cr - 0x80));
 int g = (int) (Y - 0.34414 * (Cb - 0x80) - 0.71414 * (Cr - 0x80));
 int b = (int) (Y + 1.77200 * (Cb - 0x80));

 r = Max(0, Min(255, r));
 g = Max(0, Min(255, g));
 b = Max(0, Min(255, b));

 return Color.FromArgb(a, r, g, b);
}

edited Oct 28 '10 at 12:26

answered Oct 28 '10 at 12:02

SunnyShah

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I think the conversion is automatic, so it is not needed explicitly. Nice solution. – qben Feb 22 '13 at 10:01

score 13 · Accepted Answer · edited Feb 26 '19 at 11:30

13

The problem comes that nearly everybody confuses YCbCr YUV and YPbPr. So literature you can find is often crappy. First you have to know if you really have YCbCr or if someone lies to you :-).

YUV coded data comes from analog sources (PAL video decoder, S-Video, ...)
YPbPr coded data also comes from analog sources but produces better color results as YUV (Component Video)
YCbCr coded data comes from digital sources (DVB, HDMI, ...)

YPbPr and YCbCr are related. Here are the right formulae:

https://web.archive.org/web/20180421030430/http://www.equasys.de/colorconversion.html

(the archive.org has been added to fix the old, broken link).

edited Feb 26 '19 at 11:30

linuxfan says Reinstate Monica

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answered Oct 28 '10 at 11:30

jdehaan

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Very Very Helpful link. Thanks for it. – SunnyShah Oct 28 '10 at 12:22
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I've updated the link with an internet archive version @GaryO – Omar Shehata Mar 03 '19 at 14:35

score 5 · Answer 3 · answered Mar 11 '13 at 07:09

Integer operation of ITU-R standard for YCbCr is (from Wikipedia)

Cr = Cr - 128 ;
Cb = Cb - 128 ;
r = Y + ( Cr >> 2 + Cr >> 3 + Cr >> 5 ) ;
g = Y - ( Cb >> 2 + Cb >> 4 + Cb >> 5) - ( Cr >> 1 + Cr >> 3 + Cr >> 4 + Cr >> 5) ;
b = Y + ( Cb + Cb >> 1 + Cb >> 2 + Cb >> 6) ;

or equivalently but more concisely to :

Cr = Cr - 128 ;
Cb = Cb - 128 ;
r = Y + 45 * Cr / 32 ;
g = Y - (11 * Cb + 23 * Cr) / 32 ;
b = Y + 113 * Cb / 64 ;

do not forget to clamp values of r, g and b within [0,255].

I believe the third line is incorrect. It should read: r = Y + ( Cr + Cr >> 2 + Cr >> 3 + Cr >> 5 ) ; — Michael Steinberg, Mar 17 '16 at 05:17

score 3 · Answer 4 · answered Oct 28 '10 at 10:42

3

Check out this page. It contains useful information on conversion formulae.

As an aside, you could return a unsigned int with the values for RGBA encoded from the most significant byte to least significant byte, i.e.

unsigned int YCbCrToRGBA(unsigned char Y, unsigned char Cb, unsigned char Cb) {
   unsigned char R = // conversion;
   unsigned char G = // conversion;
   unsigned char B = // conversion;

   return (R << 3) + (G << 2) + (B << 1) + 255;
}

answered Oct 28 '10 at 10:42

Adrian Regan

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I am looking for correct conversion forumla only. Because I am finding it different everywhere. Even I am also expert in C,C++. :-) – SunnyShah Oct 28 '10 at 10:48
The site I pointed you to is pretty definitive, but I know where you are coming from with regards to different perspectives on color space conversion. – Adrian Regan Oct 28 '10 at 10:54

Function to convert YCbCr to RGB?

4 Answers4