ios：UIImage比例，UIImage和他对应的CGimage不一样

Question

我有这段代码，其中self 是 UIImage 对象：

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;

但是当我使用函数UIImagePNGRepresentation 来获取字节数据以通过互联网传输时，我的图像字节在缩放后具有另一个大小。

当我使用[newImage CGImage] 时，在这段代码之后，我得到了相同的错误尺寸。

所以，我认为UIImagePNGRepresentation 使用 CGImage 从图像中获取数据字节。

那么，如何做到 UIImage 和 CGI​​mage 相同呢？

Answer 1

//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;
}

当您需要 CGImage 时，只需访问任何 UIImage 的 CGImage 属性即可获取它，如下所示

CGImage *myCGImage = myUIImage.CGImage;