GPUImage Photo(Still)/Video - Color Degradation/Too Much Brightness

Mar 02, 2014

I have mentioned this problem before in my previous post GPUImage Movie Writer Exposure Problem.

I thought I have solved problem but still the color rendered in GPUImageView is weird - it doesn’t look that much nature. I re-examine the change and find there is some sample code called GLCameraRipple from Apple which pretty much does same thing - color conversion from YUV to RGB.

After I download and check the code in GLCameraRipple, I find that actually the shader is pretty much the same. I changed the shader string to what I mentioned in GPUImage Movie Writer Exposure Problem, tried it out but the rendered image still isn’t right.

Then I trace from shader string down to the configurations/settings of the OpenGL ES, more specifically the texture uploading.

Here are the code in GPUImageVideoCamera.m:

 
// Y-plane
glActiveTexture(GL_TEXTURE4);
if ([GPUImageContext deviceSupportsRedTextures])
{
//                err = CVOpenGLESTextureCacheCreateTextureFromImage(kCFAllocatorDefault, coreVideoTextureCache, cameraFrame, NULL, GL_TEXTURE_2D, GL_RED_EXT, bufferWidth, bufferHeight, GL_RED_EXT, GL_UNSIGNED_BYTE, 0, &luminanceTextureRef);
    err = CVOpenGLESTextureCacheCreateTextureFromImage(kCFAllocatorDefault, coreVideoTextureCache, cameraFrame, NULL, GL_TEXTURE_2D, GL_LUMINANCE, bufferWidth, bufferHeight, GL_LUMINANCE, GL_UNSIGNED_BYTE, 0, &luminanceTextureRef);
}
else
{
    err = CVOpenGLESTextureCacheCreateTextureFromImage(kCFAllocatorDefault, coreVideoTextureCache, cameraFrame, NULL, GL_TEXTURE_2D, GL_LUMINANCE, bufferWidth, bufferHeight, GL_LUMINANCE, GL_UNSIGNED_BYTE, 0, &luminanceTextureRef);
}

You would probably wonder why those two code in both branches is the same.As you see, the only difference is that GL_RED_EXT vs GL_LUMINANCE. Then I’m curious about which value is used in apple’s sample code.

Open file RippleViewController.m, scroll down then you can see the following code snippet:

 
// CVOpenGLESTextureCacheCreateTextureFromImage will create GLES texture
// optimally from CVImageBufferRef.

// Y-plane
glActiveTexture(GL_TEXTURE0);
err = CVOpenGLESTextureCacheCreateTextureFromImage(kCFAllocatorDefault, 
                                                   _videoTextureCache,
                                                   pixelBuffer,
                                                   NULL,
                                                   GL_TEXTURE_2D,
                                                   GL_RED_EXT,
                                                   _textureWidth,
                                                   _textureHeight,
                                                   GL_RED_EXT,
                                                   GL_UNSIGNED_BYTE,
                                                   0,
                                                   &_lumaTexture);
if (err) 
{
    NSLog(@"Error at CVOpenGLESTextureCacheCreateTextureFromImage %d", err);
}

So the shader string is much the same, well the texture uploading settings is different. I tried to change all the settings in GPUImageVideoCamera.m and GPUImageMovie.m.

Now run the app again, compare the image with previous one, this time it looks fine.

The complete code change is in this commit: fix color degradation.