ios: UIImage scale, UIImage and his appropriate CGimage are not identical

Question

i have this code, where self is UIImage object:

CGFloat scale = [sideSize floatValue] / MIN(self.size.width, self.size.height);
 UIGraphicsBeginImageContextWithOptions(CGSizeMake(self.size.width*scale,self.size.height*scale), NO, 0.0);
[self drawInRect:CGRectMake(0, 0, self.size.width*scale, self.size.height*scale)];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
SBLog(@"%f, %f", newImage.size.width, newImage.size.height);
return newImage;

But when i use function UIImagePNGRepresentation to get bytes data to transfer via internet, i have bytes of image that have another size after scale.

More over after this code when i use [newImage CGImage] i get the same bad size.

So, i think UIImagePNGRepresentation use CGImage to get data bytes from image.

So, how to do identical UIImage and CGImage?

What you exactly mean by "how to do identical UIImage and CGImage" ? — CodenameLambda1, Aug 14 '13 at 10:30
Make size identical. I want to get data of scaled image and transfer them, so i don't want to transfer bigger image. How can i get representation in bytes of scaled image. — Logioniz, Aug 14 '13 at 11:57
This means that you have certain size limit fixed for an image and if an image is bigger than this limit, you want to reduce the image to its limit size and then transfer it. Is that correct ? — CodenameLambda1, Aug 14 '13 at 12:06
i have decision of this task to resize CGImage, but it very bigger for this small task what i think — Logioniz, Aug 14 '13 at 12:13

score 0 · Answer 1 · answered Aug 14 '13 at 12:15

//This method will resize the original image to desired width 
//maintaining the Aspect Ratio
-(UIImage*)getResizedToWidth:(CGFloat)width
{
    UIImage *resultImage = nil;

    CGFloat ar = self.size.width/self.size.height;
    CGFloat ht = width/ar;

    CGSize newSize = CGSizeMake(width, ht);

    UIGraphicsBeginImageContext(newSize);
    CGContextRef ctx = UIGraphicsGetCurrentContext();

    CGContextScaleCTM(ctx, 1, -1);
    CGContextTranslateCTM(ctx, 0, -newSize.height);

    CGRect imageRect = CGRectMake(0, 0, newSize.width, newSize.height);

    CGContextDrawImage(ctx, imageRect, self.CGImage);

    resultImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return resultImage;
}

//This method will resize the original image to desired height 
//maintaining the Aspect Ratio
-(UIImage*)getResizedToHeight:(CGFloat)height
{
    UIImage *resultImage = nil;

    CGFloat ar = self.size.width/self.size.height;
    CGFloat wd = height*ar;

    CGSize newSize = CGSizeMake(wd, height);

    UIGraphicsBeginImageContext(newSize);
    CGContextRef ctx = UIGraphicsGetCurrentContext();

    CGContextScaleCTM(ctx, 1, -1);
    CGContextTranslateCTM(ctx, 0, -newSize.height);

    CGRect imageRect = CGRectMake(0, 0, newSize.width, newSize.height);

    CGContextDrawImage(ctx, imageRect, self.CGImage);

    resultImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return resultImage;
}

//This method will take in the maxSizeLength and automatically
// detect the maximum side in image and reduce it to given
// maxSideLength maintaining the Aspect Ratio
-(UIImage*)getResizedMaxSideToLength:(CGFloat)maxSideLength
{
    UIImage *src = [UIImage imageWithCGImage:self.CGImage];

    if (src.size.width > maxSideLength)
    {
        src = [src getResizedToWidth:maxSideLength];
    }
    else
    if (src.size.height >= maxSideLength )
    {
        src = [src getResizedToHeight:maxSideLength];
    }

    return src;
}

When you need CGImage, then simply get it by accessing the CGImage property of any UIImage, like below

CGImage *myCGImage = myUIImage.CGImage;

In this case you'll have to fix the orientation of image prior to perform resize operations with my code. Here's a link on how to fix the orientation of image http://stackoverflow.com/questions/5427656/ios-uiimagepickercontroller-result-image-orientation-after-upload/5427890#5427890 — CodenameLambda1, Aug 19 '13 at 04:54

ios: UIImage scale, UIImage and his appropriate CGimage are not identical

1 Answers1