Im sampling an image in YCbCr from an ov7670 camera and using jpegant library to encode a jpeg file. Whenever I do it directly using Y,Cb,Cr values from my camera, I get a pink-violet version of the image. As far as I can understand on Wikipedia, there are different YCbCr standards, so I guess my camera use a different YCbCr standard.
Since the Jpegant library comes with an RGB example, if I convert my YCbCr values to RGB and then again rgb to YCbCr (an then JPEG) through the provided example, I get the a decent result.
Is there any way to get jpeg-YCbCr from my camera YCbCr (or any other YCbCr standard)?
The camera sends me YCbCr in 4:2:2 format (that means that two sequential pixel share the same Cb and Cr channels), I proceed to downsample them to 4:2:0 ;
Encode those samples into jpeg and get a pink-violet image ;
I convert camera YCbCr to RGB this way :
R = Y + 1.402 * (Cr - 128) G = Y + 1.772 * (Cb - 128) B = Y - 0.34414 * (Cb - 128) - 0.71414 * (Cr- 128)
Those values are good, I checked. I then convert them back into YCbCr using the formula provided with the library example:
Y' = 0.299*R + 0.587*G + 0.114*B Cb' = -0.1687*R - 0.3313*G + 0.5*B + 128 Cr' = 0.5*R - 0.4187*G - 0.0813*B + 128
With new values, it encodes correctly .
Example YCbCr of values :
156 144 145
177 105 129