NV12ToARGB function problem, the color is inaccurate

[GoogleCodeExporter]

What steps will reproduce the problem?
1. use NV12ToARGB function to convert yuv preview frame which captured by 
Android Camera
2. Watching plants slice with a microscope, the image should be green, but the 
color is A little bluer.
3. Use Android Camera App, the color is OK.

What is the expected output? What do you see instead?
The color should same as Android Camera preview. But what i see is a litter 
bluer.


What version of the product are you using? On what operating system?
verison: r1191   on android

Please provide any additional information below.

pleas refer the attached two image, the GPUImage Sample's image is also too 
blue.
issue link: https://github.com/CyberAgent/android-gpuimage/issues/140

it use formula：

//===== Approximation =============
// R = Y + 1.40625Cr
// G = Y - 0.15625Cb - 0.28125Cr
// B = Y + 1.765625Cb
//=================================
R = Y + Cr + (Cr >> 2) + (Cr >> 3) + (Cr >> 5);
if(R < 0) R = 0; else if(R > 255) R = 255;
G = Y - (Cb >> 2) + (Cb >> 4) + (Cb >> 5) - (Cr >> 1) + (Cr >> 3) + (Cr >> 4) + 
(Cr >> 5);
if(G < 0) G = 0; else if(G > 255) G = 255;
B = Y + Cb + (Cb >> 1) + (Cb >> 2) + (Cb >> 6);
if(B < 0) B = 0; else if(B > 255) B = 255;


another formula is still not OK

//Method 3
//==============================
//R = Y + 1.402Cr
//G = Y - 0.34414Cb - 0.71414Cr
//B = Y + 1.772Cb
//==============================
//===== Approximation ==========
// R = Y + 1.40625Cr
// G = Y - 0.34375Cb - 0.71875Cr
// B = Y + 1.765625Cb
//==============================
R = Y + Cr + (Cr >> 2) + (Cr >> 3) + (Cr >> 5);
if(R < 0) R = 0; else if(R > 255) R = 255;
G = Y - (Cb >> 1) + (Cb >> 3) + (Cb >> 5) - Cr + (Cr >> 2) + (Cr >> 5);
if(G < 0) G = 0; else if(G > 255) G = 255;
B = Y + Cb + (Cb >> 1) + (Cb >> 2) + (Cb >> 6);
if(B < 0) B = 0; else if(B > 255) B = 255;


I try to use another formula, the color of image is OK, but i don't know how to 
change NV12ToARGB function 

//Method 4
//==============================
//R = 1.164Y + 2.018Cr;
//G = 1.164Y - 0.813Cb - 0.391Cr;
//B = 1.164Y + 1.596Cb;
//==============================
//===== Approximation ==========
// R = 1.1640625Y + 2.015625Cr
 // G = 1.1640625Y - 0.8125Cb - 0.375Cr
// B = 1.1640625Y + 1.59375Cb
//==============================
Y = Y + (Y >> 3) + (Y >> 5) + (Y >> 7);
R = Y + (Cr << 1) + (Cr >> 6);
if(R < 0) R = 0; else if(R > 255) R = 255;
G = Y - Cb + (Cb >> 3) + (Cb >> 4) - (Cr >> 1) + (Cr >> 3);
if(G < 0) G = 0; else if(G > 255) G = 255;
B = Y + Cb + (Cb >> 1) + (Cb >> 4) + (Cb >> 5);
if(B < 0) B = 0; else if(B > 255) B = 255;

Original issue reported on code.google.com by Hoo.Zh...@gmail.com on 9 Dec 2014 at 8:53

Attachments:

• GPUImage_Sample.jpg
• Android_Camera.jpg