I'm trying to resize JPEG image in Objective-C (iOS). Input is a JPG file and output should be UIImage
.
I have this code:
// Load image from a file
NSData *imageData = [NSData dataWithContentsOfFile:jpgFile];
UIImage *inputImage = [UIImage imageWithData:imageData];
CIImage *ciImage = inputImage.CIImage;
// Set Lanczos filter
CIFilter *scaleFilter = [CIFilter filterWithName:@"CILanczosScaleTransform"];
[scaleFilter setValue:ciImage forKey:@"inputImage"];
[scaleFilter setValue:[NSNumber numberWithFloat:0.5] forKey:@"inputScale"];
[scaleFilter setValue:[NSNumber numberWithFloat:1.0] forKey:@"inputAspectRatio"];
// Get an output
CIImage *finalImage = [scaleFilter valueForKey:@"outputImage"];
UIImage *outputImage = [[UIImage alloc] initWithCIImage:finalImage];
But the output image is invalid ( outputImage.size.height is 0
), and it causes following errors in an other processing:
CGContextDrawImage: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable. ImageIO: JPEG Empty JPEG image (DNL not supported)
I don't know, what is wrong with the code above (except the initialization mentioned by Sulthan below - thank him for that). I used following code at the end (this code works OK):
CIImage *input_ciimage = [[CIImage alloc] initWithImage:inputImage]; CIImage *output_ciimage = [[CIFilter filterWithName:@"CILanczosScaleTransform" keysAndValues: kCIInputImageKey, input_ciimage, kCIInputScaleKey, [NSNumber numberWithFloat:0.5], nil] outputImage]; CIContext *context = [CIContext contextWithOptions:nil]; CGImageRef output_cgimage = [context createCGImage:output_ciimage fromRect:[output_ciimage extent]]; UIImage *output_uiimage = [UIImage imageWithCGImage:output_cgimage]; CGImageRelease(output_cgimage);
This line is the problem:
CIImage *ciImage = inputImage.CIImage
If the image is not initialized from a CIImage
then it's own CIImage
is nil
. A safer approach is:
CIImage *ciImage = [[CIImage alloc] initWithImage:inputImage];
Also, make sure the image has been loaded successfully from your data.
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