How do I reduce Image quality/size in iPhone objective-c?

问题

I have an app that lets the user take a picture with his/her iPhone and use it as a background image for the app. I use UIImagePickerController to let the user take a picture and set the background UIImageView image to the returned UIImage object.

IBOutlet UIImageView *backgroundView;

-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)image editingInfo:(NSDictionary *)editingInfo {
 backgroundView.image = image;
 [self dismissModalViewControllerAnimated:YES];
}

This all works fine. How can I reduce the size of the UIImage to 480x320 so my app can be memory efficient? I don't care if I loose any image quality.

Thanks in advance.

回答1:

You can create a graphics context, draw the image into that at the desired scale, and use the returned image. For example:

UIGraphicsBeginImageContext(CGSizeMake(480,320));

CGContextRef            context = UIGraphicsGetCurrentContext();

[image drawInRect: CGRectMake(0, 0, 480, 320)];

UIImage        *smallImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

回答2:

I know this question is already solved, but just if someone (like i did) wants to scale the image keeping the aspect ratio, this code might be helpful:

-(UIImage *)resizeImage:(UIImage *)image toSize:(CGSize)size
{
    float width = size.width;
    float height = size.height;

    UIGraphicsBeginImageContext(size);
    CGRect rect = CGRectMake(0, 0, width, height);

    float widthRatio = image.size.width / width;
    float heightRatio = image.size.height / height; 
    float divisor = widthRatio > heightRatio ? widthRatio : heightRatio;

    width = image.size.width / divisor; 
    height = image.size.height / divisor;

    rect.size.width  = width;
    rect.size.height = height;

    if(height < width)
        rect.origin.y = height / 3;

    [image drawInRect: rect];

    UIImage *smallImage = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();   

    return smallImage;
}

回答3:

Use contentOfFile and make sure that all of your images are .png. Apple is optimized for png.

Oh, use the contentOfFile not the imageName method. Several reasons for that. Images that is brought in memory by ImageName remained in memory even after a [release] is called.

Dont ask my why. The apple told me so.

Roydell Clarke

来源：https://stackoverflow.com/questions/2079543/how-do-i-reduce-image-quality-size-in-iphone-objective-c

标签

objective-c

ios

uiimage

uiimagepickercontroller