我知道这个问题已经被问过好几次了,但他们的回答让我的图像质量下降。他们都变得像素化。因此,即使它正确地裁剪和调整大小,它也会降低质量。
只是为了让您检查一下,这是每个帖子中的算法:
- (UIImage*)scaleAndCropImage:(UIImage *)aImage forSize:(CGSize)targetSize
{
UIImage *sourceImage = aImage;
UIImage *newImage = nil;
CGSize imageSize = sourceImage.size;
CGFloat width = imageSize.width;
CGFloat height = imageSize.height;
CGFloat targetWidth = targetSize.width;
CGFloat targetHeight = targetSize.height;
CGFloat scaleFactor = 0.0;
CGFloat scaledWidth = targetWidth;
CGFloat scaledHeight = targetHeight;
CGPoint thumbnailPoint = CGPointMake(0.0,0.0);
if (CGSizeEqualToSize(imageSize, targetSize) == NO)
{
CGFloat widthFactor = targetWidth / width;
CGFloat heightFactor = targetHeight / height;
if (widthFactor > heightFactor)
{
scaleFactor = widthFactor; // scale to fit height
}
else
{
scaleFactor = heightFactor; // scale to fit width
}
scaledWidth = width * scaleFactor;
scaledHeight = height * scaleFactor;
// center the image
if (widthFactor > heightFactor)
{
thumbnailPoint.y = (targetHeight - scaledHeight) * 0.5;
}
else
{
if (widthFactor < heightFactor)
{
thumbnailPoint.x = (targetWidth - scaledWidth) * 0.5;
}
}
}
UIGraphicsBeginImageContext(targetSize); // this will crop
CGRect thumbnailRect = CGRectZero;
thumbnailRect.origin = thumbnailPoint;
thumbnailRect.size.width = scaledWidth;
thumbnailRect.size.height = scaledHeight;
[sourceImage drawInRect:thumbnailRect];
newImage = UIGraphicsGetImageFromCurrentImageContext();
if(newImage == nil)
{
NSLog(@"could not scale image");
}
//pop the context to get back to the default
UIGraphicsEndImageContext();
return newImage;
}
最佳答案
在开始 UIGraphicsImageContext 的行中,使用 UIGraphicsBeginImageContextWithOptions
而不是 UIGraphicsBeginImageContext
。尝试这样的事情:
UIGraphicsBeginImageContextWithOptions(targetSize, NO, 0.0)
请注意上面传递的三个参数,我将按顺序逐一介绍:
targetSize
是以点(而不是像素)测量的图像大小NO
是一个 BOOL 值(可以是 YES 或 NO),指示图像是否 100% 不透明。将此设置为 NO 将保留透明度并创建一个 alpha channel 来处理透明度。- 上述代码中最重要的部分是最后一个参数,
0.0
。这是将要应用的图像比例因子。将值指定为0.0
会设置当前设备屏幕的比例因子。这意味着质量将得到保留,并且在 Retina 显示器上看起来特别好。
这是 Apple Documentation在 UIGraphicsBeginImageContextWithOptions
上。
关于objective-c - UIImage 调整大小并裁剪以适合框架,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/17725959/