UIGraphicsBeginImageContextWithOptions 和 UIImageJPEGRepresentation 不能很好地协同工作

发布于 2024-11-28 12:15:49 字数 715 浏览 1 评论 0原文

所以我有这段代码来创建一个 UIImage：

UIGraphicsBeginImageContextWithOptions(border.frame.size, YES, 0);
[border.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *thumbnailImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

此时，图像的尺寸是正确的，80x100。

然后它运行以下代码：

NSData *fullImageData = UIImageJPEGRepresentation(image, 1.0f);

图像的 NSData 返回尺寸为 160x200 的图像 - 是应有尺寸的两倍。

很明显，原因是这一行：

UIGraphicsBeginImageContextWithOptions(border.frame.size, YES, 0);

末尾的 0 是比例，因为它是 0，所以它按照设备比例因素。我保持这种方式是为了保持清晰的图像。然而，当我将图像设置为 1 时，尽管图像保持应有的大小，但它并没有以视网膜质量显示。我想做的是保持它的视网膜质量，但也保持它在正确的尺寸。有办法做到这一点吗？

原文

So i have this code to create a UIImage:

UIGraphicsBeginImageContextWithOptions(border.frame.size, YES, 0);
[border.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *thumbnailImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

At this point, the size on the image is correct, 80x100.

Then it runs this code:

NSData *fullImageData = UIImageJPEGRepresentation(image, 1.0f);

And the NSData of the image returns an image at the size 160x200 - twice as much as it should be.

It's became clear the reason for this is the line:

UIGraphicsBeginImageContextWithOptions(border.frame.size, YES, 0);

The 0 on the end is the scale, and because it's 0 it goes by the devices scale factor. I keep it this way to maintain a clear image. However, when i set the image to 1, despite the image staying the size it should, it doesn't come out in retina quality. What i want to do is keep it in retina quality, but also keep it at the right size. Is there a way to do this?

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知你几分 2024-12-05 12:15:49

在调用 UIImageJPEGRepresentation 之前尝试调整 UIImage 的大小

- (UIImage *)resizeImage:(UIImage*)image newSize:(CGSize)newSize {
    CGRect newRect = CGRectIntegral(CGRectMake(0, 0, newSize.width, newSize.height));
    CGImageRef imageRef = image.CGImage;

    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();

    // Set the quality level to use when rescaling
    CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
    CGAffineTransform flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, newSize.height);

    CGContextConcatCTM(context, flipVertical);  
    // Draw into the context; this scales the image
    CGContextDrawImage(context, newRect, imageRef);

    // Get the resized image from the context and a UIImage
    CGImageRef newImageRef = CGBitmapContextCreateImage(context);
    UIImage *newImage = [UIImage imageWithCGImage:newImageRef];

    CGImageRelease(newImageRef);
    UIGraphicsEndImageContext();    

    return newImage;
}

if([UIScreen mainScreen].scale > 1)
    {
        thumbnailImage = [self thumbnailImage newSize:CGSizeMake(thumbnailImage.size.width/[UIScreen       mainScreen].scale, thumbnailImage.size.height/[UIScreen mainScreen].scale)];
    }

Try resizing the UIImage before calling UIImageJPEGRepresentation

- (UIImage *)resizeImage:(UIImage*)image newSize:(CGSize)newSize {
    CGRect newRect = CGRectIntegral(CGRectMake(0, 0, newSize.width, newSize.height));
    CGImageRef imageRef = image.CGImage;

    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();

    // Set the quality level to use when rescaling
    CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
    CGAffineTransform flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, newSize.height);

    CGContextConcatCTM(context, flipVertical);  
    // Draw into the context; this scales the image
    CGContextDrawImage(context, newRect, imageRef);

    // Get the resized image from the context and a UIImage
    CGImageRef newImageRef = CGBitmapContextCreateImage(context);
    UIImage *newImage = [UIImage imageWithCGImage:newImageRef];

    CGImageRelease(newImageRef);
    UIGraphicsEndImageContext();    

    return newImage;
}

if([UIScreen mainScreen].scale > 1)
    {
        thumbnailImage = [self thumbnailImage newSize:CGSizeMake(thumbnailImage.size.width/[UIScreen       mainScreen].scale, thumbnailImage.size.height/[UIScreen mainScreen].scale)];
    }

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燕归巢 2024-12-05 12:15:49

- (UIImage *)imageWithImage{
    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;

}

- (UIImage *)imageWithImage{
    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);
    [image drawInRect:CGRectMake(0, 0, newSize.width, newSize.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;

}

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