EAGLView to UIImage color conversion issue

问题

I have an EAGLView (taken from Apple's examples) which I can successfully convert to a UIImage using this code:

- (UIImage *)glToUIImage:(CGSize)size {

NSInteger backingWidth = size.width;
NSInteger backingHeight = size.height;

NSInteger myDataLength = backingWidth * backingHeight * 4;

// allocate array and read pixels into it.
GLuint *buffer = (GLuint *) malloc(myDataLength);
glReadPixels(0, 0, backingWidth, backingHeight, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

// gl renders “upside down” so swap top to bottom into new array.
for(int y = 0; y < backingHeight / 2; y++) {
    for(int x = 0; x < backingWidth; x++) {
        //Swap top and bottom bytes
        GLuint top = buffer[y * backingWidth + x];
        GLuint bottom = buffer[(backingHeight - 1 - y) * backingWidth + x];
        buffer[(backingHeight - 1 - y) * backingWidth + x] = top;
        buffer[y * backingWidth + x] = bottom;
    }
}

// make data provider with data.
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer, myDataLength, releaseScreenshotData);

// prep the ingredients
const int bitsPerComponent = 8;
const int bitsPerPixel = 4 * bitsPerComponent;
const int bytesPerRow = 4 * backingWidth;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGBitmapByteOrderDefault;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;

// make the cgimage
CGImageRef imageRef = CGImageCreate(backingWidth, backingHeight, bitsPerComponent, bitsPerPixel, bytesPerRow, colorSpaceRef, bitmapInfo, provider, NULL, YES, renderingIntent);
CGColorSpaceRelease(colorSpaceRef);
CGDataProviderRelease(provider);

// then make the UIImage from that
UIImage *myImage = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);

return myImage;

}

void releaseScreenshotData(void *info, const void *data, size_t size) {
free((void *)data);
};

And here is the code where I use this method to convert to a UIImage:

EAGLView *newView = [[EAGLView alloc] initWithImage:photo.originalImage];

[newView reshapeFramebuffer];
[newView drawView:theSlider.tag value:theSlider.value];
//the two lines above are how EAGLViews in Apple's examples are modified


photoItem *newPhoto = [[photoItem alloc] initWithImage:[self glToUIImage:photo.originalImage.size]];

The problem I am having is, sometimes the converted UIImage won't have the same colors as the EAGLView. This occurs if I apply a high saturation to the EAGLView, or high brigtness, or low contrast, and some other cases. For example, if I apply a high saturation to the EAGLView, and then convert to UIImage, some parts of the image will be brighter than what it's suppose to be.

So I discovered that the problem was a EAGLView timing issue in disguise, similar to my previous question here (EAGLView to UIImage timing question).

回答1:

For anyone that still cares see my comment below:

Tommy, I finally hacked my way into a solution. It was another EAGLView timing issue (which only showed up during Saturation actually), and I was able to fix it with your performSelector:afterDelay:0.0 approach. Thx

Also, I would recommend anyone coding for iOS 5.0 to look into Core Image and GLKView. They basically make your job of adjusting image properties (as I am doing here) and EAGLView to UIImage conversion type of stuff much simpler.

来源：https://stackoverflow.com/questions/7086468/eaglview-to-uiimage-color-conversion-issue

标签

iphone

ios

uiview

opengl-es

eaglview