iPhone 4s-UIImage CGImage图像尺寸

Question

I have a crash which only occurs on 4S (not on 3GS). I am doubting its because of @2x. Basically I get raw bytes of image and manipulate. Here's the question I have.

I load a image as mentioned in the sample code below. At the end, uiWidth should be 2000 and cgwidth should be 2000. Correct? (Would it still be true if image is loaded from camera rolls? Or its autoscaling and uiWidth will be 4000?)

//test.jpg is 2000x 1500 pixels.
NSString *fileName = [[NSBundle mainBundle] pathForResource:@"test" ofType:@"jpg"];
UIImage *image = [UIImage imageWithContentsOfFile:fileName];

int uiWidth = image.size.width;

CGImageRef cgimg = image.CGImage;

int cgWidth = CGImageGetWidth(cgimg);

Thank you for your help.

Answer 1

The size reported by UIImage is in points, not pixels. You need to take into account the scale property of UIImage .

In other words, if test.jpg is 1000x1000 then UIImage.size will report 1000x1000. If test@2x.png is 2000x2000 then UIImage.size will also report 1000x1000. But in the 2nd case, UIImage.scale will report 2.

CGImageGetWidth reports its width in pixels, not points.