Creating UIImage from context of UIImageView

Question

So I am cropping an image with a UIImageView which may or may not be very efficient. I'm some what a n00b when it comes to Graphics programming. When all my code runs I am stuck with a white image and I'm not quite sure why.

I took a look at this: Crop and save visible region of UIImageView using AspectFill and have had no success. Here is my code:

imageFile = [info objectForKey:UIImagePickerControllerOriginalImage];

selectedImage.hidden = false;  //selectedImage is my UIImageView
selectedImage.image = imageFile;

UIGraphicsBeginImageContext(selectedImage.frame.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGImageRef image = CGBitmapContextCreateImage(context);

float width = CGImageGetWidth(image);
float height = CGImageGetHeight(image);

CGImageRef cropped_img = CGImageCreateWithImageInRect(image, CGRectMake(0, 0, width, height));

imageFile = [UIImage imageWithCGImage:cropped_img];
imageFile = [UIImage imageWithData:UIImageJPEGRepresentation(imageFile, 0.05f)];

selectedImage.image = imageFile;  //Final product is white

So selectedImage is my UIImageView and that is what ends up being white. Any help would greatly be appreciated.

Answer 1

Maybe this line?

imageFile = [UIImage imageWithData:UIImageJPEGRepresentation(imageFile, 0.05f)];

If you are getting a UIImage from the line directly above it I would not think you would then need to pass it through at an extremely low JPEG compression rate. 0 being the lowest quality, maybe it's so low it looks white. Try removing that line and or changing the compression.

Answer 2

In these lines

CGContextRef context = UIGraphicsGetCurrentContext();
CGImageRef image = CGBitmapContextCreateImage(context);

you create a new context, that will be blank (white) and then create an image from this. So your resulting image will just be white.

The function CGImageCreateWithImageInRect needs a CGImageRef , which you can get from a UIImage easily with

CGImageCreateWithImageInRect(imageFile.CGImage, CGRectMake(0, 0, width, height));

---

Not sure why you are doing this line

imageFile = [UIImage imageWithData:UIImageJPEGRepresentation(imageFile, 0.05f)];

This will just give you a poor quality image :/

Answer 3

I found the solution from this SO post: Creating UIImage from context of UIImageView

Here's the solution:

I needed to import the Quartz Core Framework: #import <QuartzCore/QuartzCore.h>

Then I used the following method:

- (UIImage*)imageFromImageView:(UIImageView*)imageView
{
    UIGraphicsBeginImageContext(imageView.frame.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextRotateCTM(context, 2*M_PI);

    [imageView.layer renderInContext:context];
    UIImage *image =  UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return image;
}