How to resize CIImage?

Question

I need to resize more image in one "for" but if I use UIGraphicsGetImageFromCurrentImageContext, I don't have enough memory for more images, because it stay on autorelease and images released when "for" is terminated. I need another method for resize. Any ideas. Thanks

-(UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize {
CGSize targetSize = newSize;      
CGSize imageSize = image.size;
CGFloat width = imageSize.width;
CGFloat height = imageSize.height;
CGFloat targetWidth = targetSize.width;
CGFloat targetHeight = targetSize.height;
CGFloat scaleFactor = 0.0;
CGFloat scaledWidth = targetWidth;
CGFloat scaledHeight = targetHeight;
CGPoint thumbnailPoint = CGPointMake(0.0,0.0);

if (CGSizeEqualToSize(imageSize, targetSize) == NO) 
{
    CGFloat widthFactor = targetWidth / width;
    CGFloat heightFactor = targetHeight / height;

    if (widthFactor > heightFactor) 
        scaleFactor = widthFactor; // scale to fit height
    else
        scaleFactor = heightFactor; // scale to fit width
    scaledWidth  = width * scaleFactor;
    scaledHeight = height * scaleFactor;

    // center the image
    if (widthFactor > heightFactor)
    {
        thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5; 
    }
    else 
        if (widthFactor < heightFactor)
        {
            thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
        }
}       

UIGraphicsBeginImageContext(targetSize); // this will crop

CGRect thumbnailRect = CGRectZero;
thumbnailRect.origin = thumbnailPoint;
thumbnailRect.size.width  = scaledWidth;
thumbnailRect.size.height = scaledHeight;

[image drawInRect:thumbnailRect];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
//pop the context to get back to the default
UIGraphicsEndImageContext();

return newImage;
}


-(void)preparePhotosForResolution:(CGSize)resolution {
NSLog(@"Resolution : %f,%f",resolution.width,resolution.height);
NSFileManager *fm = [NSFileManager defaultManager];
NSString *tmpPath = [projectPath stringByAppendingPathComponent:@"temp"];
[fm removeItemAtPath:tmpPath error:nil];
[fm createDirectoryAtPath:tmpPath withIntermediateDirectories:YES attributes:nil error:nil];
for (int i = 0; i < [sortArray count]; i++) {
    UIImage *image = [[UIImage alloc] initWithContentsOfFile:[projectPath stringByAppendingPathComponent:[sortArray objectAtIndex:i]]];
    UIImage *newImage = [self imageWithImage:image scaledToSize:resolution];
    [image release];
    NSData *imgData = UIImagePNGRepresentation(newImage);
    [fm createFileAtPath:[tmpPath stringByAppendingPathComponent:[sortArray objectAtIndex:i]] contents:imgData attributes:nil];
}
}

According to Google Translate, Andrew's comment is "Bai you are bald, so you do not know answer to question". In the meantime, Igor, can you show the code that you use to resize your images? That might help me or anyone else to come up with an answer to your image resizing problem. — Michael Dautermann, Feb 02 '12 at 16:33
exactly translate is "Hey, you are skin, so you don't know answer to question" ;) — Igor Bidiniuc, Feb 02 '12 at 17:08
@IgorBidiniuc Please take a look here: http://stackoverflow.com/questions/5860215/resizing-a-uiimage-without-loading-it-entirely-into-memory — Costique, Feb 02 '12 at 17:20

score 3 · Answer 1 · answered Jun 01 '18 at 10:15

3

    CIFilter *filter = [CIFilter filterWithName:@"CILanczosScaleTransform"];
    [filter setValue:newImage forKey:@"inputImage"];
    [filter setValue:@(scale) forKey:@"inputScale"];
    [filter setValue:@1.0 forKey:@"inputAspectRatio"];
    newImage = filter.outputImage;

answered Jun 01 '18 at 10:15

charvel

221
2
5

5

Welcome to SO. You need to include an explanation as to why your code is the right answer as well. – Nick Jun 01 '18 at 10:41
Please, explain your answer to improve its quality. – Andrea Mario Lufino Jun 01 '18 at 14:11
What is the scale in this instance? How do you define it? – Alan S Sep 26 '19 at 13:33
https://developer.apple.com/documentation/coreimage/cilanczosscaletransform?language=objc I hope this will assist a bit. Also, on the same topic: https://nshipster.com/image-resizing/ – YanivH Apr 17 '20 at 13:56

score -1 · Answer 2 · answered Apr 26 '23 at 11:00

With above objective-c code in swift.

inputImage = CIImage
inputScale       =  targetSize.width / originalSize.width
inputAspectRatio =  targetSize.width / (originalSize.width * resizeRatio)


    let resizeFilter = CIFilter(name: "CILanczosScaleTransform")
    resizeFilter?.setValue(inputImage, forKey: "inputImage")
    resizeFilter?.setValue(inputScale, forKey: "inputScale")
    resizeFilter?.setValue(inputAspectRatio, forKey: "inputAspectRatio")
    
    let outputImage = resizeFilter?.outputImage

How to resize CIImage?

2 Answers2