CGImage of UIImage return NULL - objective-c

Question

I created a function for splitting an image into multiple images, but when I take take the CGImage of the UIImage, the CGImage returns NULL
NSArray* splitImage(UIImage* image,NSUInteger pieces) {
NSLog(#"width: %f, %zu",image.size.width,CGImageGetWidth(image.CGImage));
NSLog(#"%#",image.CGImage);
returns NULL
NSMutableArray* tempArray = [[NSMutableArray alloc]initWithCapacity:pieces];
CGFloat piecesSize = image.size.height/pieces;
for (NSUInteger i = 0; i < pieces; i++) {
// take in account retina displays
CGRect subFrame = CGRectMake(0,i * piecesSize * image.scale ,image.size.width * image.scale,piecesSize * image.scale);
CGImageRef newImage = CGImageCreateWithImageInRect(image.CGImage,subFrame);
UIImage* finalImage =[UIImage imageWithCGImage:newImage];
CGImageRelease(newImage);
[tempArray addObject:finalImage];
}
NSArray* finalArray = [NSArray arrayWithArray:tempArray];
[tempArray release];
return finalArray;
}

Answer 1

I have created UIImage from CGImage.
CIImage *ciImage = image.CIImage;
CIContext *context = [CIContext contextWithOptions:nil];
CGImageRef ref = [context createCGImage:ciImage fromRect:ciImage.extent];
UIImage *newImage = [UIImage imageWithCGImage:ref];
And now newImage.CGImage is not nil

Answer 2

The CGImage property will return nil if the UIImage was created from another image such as an IOSurface or CIImage. To get around this in this particular case I can create a CGImage from an IOSurface using the c function then convert that to a UIImage.
UICreateCGImageFromIOSurface(IOSurfaceRef surface);

Answer 3

Convert CGImage to UIImage with this and cgImage will not be null:
func convert(cmage:CIImage) -> UIImage
{
let context:CIContext = CIContext.init(options: nil)
let cgImage:CGImage = context.createCGImage(cmage, from: cmage.extent)!
let image:UIImage = UIImage.init(cgImage: cgImage)
return image
}

Answer 4

What you did now is just create pieces with 0.f width, you should use two fors to define the width & height for your pieces. Code sample like this (not tested yet, but it should works):
for (int height = 0; height < image.size.height; height += piecesSize) {
for (int width = 0; width < image.size.width; width += piecesSize) {
CGRect subFrame = CGRectMake(width, height, piecesSize, piecesSize);
CGImageRef newImage = CGImageCreateWithImageInRect(image.CGImage, subFrame);
UIImage * finalImage = [UIImage imageWithCGImage:newImage];
CGImageRelease(newImage);
[tempArray addObject:finalImage];
}
}

Answer 5

It happens in some cases when we try to crop image. I found the solution like this try this may be this can help you:-
NSData *imageData = UIImageJPEGRepresentation(yourImage, 0.9);
newImage = [UIImage imageWithData:imageData];