Try to save image in background - iphone

Question

I'm trying to call UIImagePNGRepresentation in other than main thread, but I'm getting only the EXC_BAD_ACCESS exception.
Here is code
UIImage *imageToSave = [UIImage imageWithCGImage:imageRef];
dispatch_queue_t taskQ = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(taskQ,
^{
NSData *binaryImage = UIImagePNGRepresentation(imageToSave);
if (![binaryImage writeToFile:destinationFilePath atomically:YES]) {
SCASSERT(assCodeCannotCreateFile, #"Write of image file failed!");
};
});
Exception occours when trying to access imageToSave variable.
EDIT:
I want to save OpenGL sceene to PNG file, there is code of whole function
- (void)saveImage:(NSString *)destinationFilePath {
NSUInteger width = (uint)self.frame.size.width;
NSUInteger height = (uint)self.frame.size.height;
NSUInteger myDataLength = width * height * 4;
// allocate array and read pixels into it.
GLubyte *buffer = (GLubyte *)malloc(myDataLength);
glReadPixels(0, 0, width, height, GL_RGBA, GL_UNSIGNED_BYTE, buffer);
// 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(myDataLength);
for (int y = 0; y <height; y++) {
for (int x = 0; x <width * 4; x++) {
buffer2[((int)height - 1 - y) * (int)width * 4 + x] = buffer[y * 4 * (int)width + x];
}
}
JFFree(buffer);
// make data provider with data.
CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, buffer2, myDataLength, NULL);
// prep the ingredients
int bitsPerComponent = 8;
int bitsPerPixel = 32;
int bytesPerRow = 4 * width;
CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB();
CGBitmapInfo bitmapInfo = kCGImageAlphaPremultipliedLast;
CGColorRenderingIntent renderingIntent = kCGRenderingIntentDefault;
// make the cgimage
CGImageRef imageRef = CGImageCreate(width,
height,
bitsPerComponent,
bitsPerPixel,
bytesPerRow,
colorSpaceRef,
bitmapInfo,
provider,
NULL,
NO,
renderingIntent);
UIImage *imageToSave = [UIImage imageWithCGImage:imageRef];
dispatch_queue_t taskQ = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0);
dispatch_async(taskQ,
^{
NSData *binaryImage = UIImagePNGRepresentation(imageToSave);
if (![binaryImage writeToFile:destinationFilePath atomically:YES]) {
SCASSERT(assCodeCannotCreateFile, #"Write of image file failed!");
};
});
// release resources
CGColorSpaceRelease(colorSpaceRef);
CGDataProviderRelease(provider);
CGImageRelease(imageRef);
JFFree(buffer2);
}

Answer 1

leave out the CGImageRelease call because the UIImage doesnt retain the CGImageRef
see imageWithCGImage and memory