Image quality with UIImageWriteToSavedPhotosAlbum - ios

Question

I am trying to get a screenshot from a GLKView and save it to Photo Library. Unfortunately the quality of the saved photo is very low and I cannot figure why.
This is the link to the UIImage displayed on the screen using ImageView class: https://www.dropbox.com/s/d2cyb099n0ndqag/IMG_0148.PNG?dl=0
This is the link to the photo saved in Photo Albums:
https://www.dropbox.com/s/8pdaytonwxxd6wk/IMG_0147.JPG?dl=0
The code is as follows:
- (UIImage*)snapshot
{
GLint backingWidth, backingHeight;
GLint framebuff;
glGetIntegerv( GL_FRAMEBUFFER_BINDING, &framebuff);
glBindFramebuffer(GL_FRAMEBUFFER, framebuff);
// Get the size of the backing CAEAGLLayer
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &backingWidth);
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &backingHeight);
NSInteger x = 0, y = 0, width = backingWidth, height = backingHeight;
NSInteger dataLength = width * height * 4;
GLubyte *data = (GLubyte*)malloc(dataLength * sizeof(GLubyte));
// Read pixel data from the framebuffer
glPixelStorei(GL_PACK_ALIGNMENT, 4);
glReadPixels(x, y, width, height, GL_RGBA, GL_UNSIGNED_BYTE, data);
GLenum errCode;
if ((errCode = glGetError()) != GL_NO_ERROR) {
//errStr = gluErrorString(errCode);
printf("%u: OpenGL ERROR ",errCode);
}
// gl renders "upside down" so swap top to bottom into new array.
// there's gotta be a better way, but this works.
GLubyte *buffer2 = (GLubyte *) malloc(dataLength);
for(int y = 0; y < height; y++)
{
for(int x = 0; x < width * 4; x++)
{
buffer2[((height - 1) - y) * width * 4 + x] = data[y * 4 * width + x];
}
}
// Create a CGImage with the pixel data
// If your OpenGL ES content is opaque, use kCGImageAlphaNoneSkipLast to ignore the alpha channel
// otherwise, use kCGImageAlphaPremultipliedLast
CGDataProviderRef ref = CGDataProviderCreateWithData(NULL, buffer2, dataLength, NULL);
CGColorSpaceRef colorspace = CGColorSpaceCreateDeviceRGB();
CGImageRef iref = CGImageCreate(width, height, 8, 32, width * 4, colorspace, kCGBitmapByteOrderDefault, ref, NULL, YES, kCGRenderingIntentDefault);
// Retrieve the UIImage from the current context
UIImage *image = [UIImage imageWithCGImage:iref];
UIImageView *myImageView = [[UIImageView alloc] init];
myImageView.frame = CGRectMake(0, 0, fluid.gpu.Drawing.Pong->width,fluid.gpu.Drawing.Pong->height);
myImageView.image = image;
[self.view addSubview:myImageView];
CFRelease(colorspace);
CGImageRelease(iref);
free(data);
return image;
}
-(void)SavePhoto{
UIImage *temp = [self snapshot];
UIImageWriteToSavedPhotosAlbum(temp, self, #selector(imageSavedToPhotosAlbum: didFinishSavingWithError: contextInfo:), (__bridge void*)self.context);
}
- (void)imageSavedToPhotosAlbum:(UIImage *)image didFinishSavingWithError:(NSError *)error contextInfo:(void *)contextInfo {
NSString *message;
NSString *title;
if (!error) {
title = NSLocalizedString(#"Save picture", #"");
message = NSLocalizedString(#"Your screenshot was saved to Photos Album.", #"");
} else {
title = NSLocalizedString(#"There was an error saving screenshot.", #"");
message = [error description];
}
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:title
message:message
delegate:nil
cancelButtonTitle:NSLocalizedString(#"OK", #"")
otherButtonTitles:nil];
[alert show];
}
I also tried the convenience method of [GLKView snapshot] but I get the same result. The problem is replicated on iPhone 4, iPhone 3Gs, IPad2

Answer 1

I manage to get a better quality by transforming my image into a PNG format and save this last one:
NSData* imdata = UIImagePNGRepresentation ( image ); // get PNG representation
UIImage* imgPng = [UIImage imageWithData:imdata]; // wrap UIImage
return imgPng;