CODEWITHSUNDEEP
mathrgb
SunnyShah
SunnyShah

Reputation: 30517

YCbCr to RGB from matrix table

Below is a matrix to convert RGB to YCbCr. Can you tell me how can I get formula to convert YCbCr to RGB? I mean, I have YCbCr value available and I want to get RGB from it. RGB to YUV Image

Upvotes: 3

Views: 21704

Answers (6)

murage kibicho
murage kibicho

Reputation: 654

These are the equations that work for 0-255 colors. Here they are in C

RGB to YCBCR

y = 0.299* (r) + 0.587 * (g)    + 0.114* (b);
cb= 128 - 0.168736* (r) - 0.331364 * (g)    + 0.5* (b);
cr= 128 + 0.5* (r)  - 0.418688 * (g)    - 0.081312* (b);

YCBCR to RGB

r = (y) + 1.402 * (cr -128);
g = (y) - 0.34414 * (cb - 128) - 0.71414 * (cr - 128);
b = (y) + 1.772 * (cb - 128);

Upvotes: 1

Валерий Заподовников
Валерий Заподовников

Reputation: 438

Convert to float and apply (since the coeff. are BT.709-2):

https://en.wikipedia.org/wiki/YCbCr#ITU-R_BT.709_conversion

1   0        1.5748
1  -0.1873  -0.4681 
1   1.8556   0

Upvotes: 1

Jacob
Jacob

Reputation: 34621

I'm not going to account for the round portion, but since M looks invertible:

alt text

You can round the resulting vector.

Upvotes: 3

Steve Tjoa
Steve Tjoa

Reputation: 61104

If you are asking how the formula is derived, you may want to search for "color coordinate systems". This page has a good discussion on the YCbCr space, in particular.

We know that almost any color can be represented as a linear combination of red, green, and blue. But you can transform (or "rotate") that coordinate system such that the three basis elements are no longer RGB, but something else. In the case of YCbCr, the Y layer is the luminance layer, and Cb and Cr are the two chrominance layers. Cb correlates more closely to blue, and Cr correlates more closely to red.

YCbCr is often preferred because the human visual system is more sensitive to changes in luminance than quantitatively equivalent changes in chrominance. Therefore, an image coder such as JPEG can compress the two chrominance layers more than the luminance layer, resulting in a higher compression ratio.

EDIT: I misunderstood the question. (You should edit it to clarify.) Here is the formula to get RGB from YCbCr, taken from the above link:

r   =   1.0 * y'    + 0 * cB    + 1.402 * cR
g   =   1.0 * y'    - 0.344136 * cB - 0.714136 * cR
b   =   1.0 * y'    + 1.772 * cB    + 0 * cR

Upvotes: 6

I82Much
I82Much

Reputation: 27326

http://www.fourcc.org/fccyvrgb.php has YUV to RGB conversions.

Upvotes: 1

Eugene Smith
Eugene Smith

Reputation: 9398

Y = 0.2126*(219/255)*R + 0.7152(219/255)*G + 0.0722*(219/255)*B + 16
CB = -0.2126/1.18556*(224/255)*R - 0.7152/1.8556(224/255)*G + 0.5*(219/255)*B + 128
CR = 0.5*(224/255)*R - 0.7152/1.5748(224/255)*G - 0.0722/1.5748*(224/255)*B + 128

Upvotes: 1

Related Questions