35

我从相机中获取 UIimages 并将它们分配给 UIImageViews 以显示。当我这样做时，相机会给我一个 1200 x 1600 像素的图像，然后我将其分配给我的应用程序中的 UIImageView。在这种情况下，图像在图像视图中按预期显示。但是，当我在将检索到的 UIImage 分配给 UIImageView 之前尝试调整它的大小时，图像正在按预期调整大小，但是在某个地方（在调整大小的代码中？）我的 UIImage 正在旋转...结果，当我将调整大小的 UIImage 分配给 UIImageView 时，图像旋转了 90 度，并且由于纵横比（1200 x 1600 像素）没有改变而显得拉伸......

我正在使用它从相机中获取 UIImage：

- (void) imagePickerController:(UIImagePickerController*)picker didFinishPickingMediaWithInfo:(NSDictionary*)info
{

        myImg = [info objectForKey:@"UIImagePickerControllerOriginalImage"];
        myResizedImg = [self resizeImage:myImg width:400 height:533];
        [myImageView setImage:myResizedImg];

}

我正在使用它来调整它的大小：

-(UIImage *)resizeImage:(UIImage *)anImage width:(int)width height:(int)height
{

    CGImageRef imageRef = [anImage CGImage];

    CGImageAlphaInfo alphaInfo = CGImageGetAlphaInfo(imageRef);

    if (alphaInfo == kCGImageAlphaNone)
    alphaInfo = kCGImageAlphaNoneSkipLast;


    CGContextRef bitmap = CGBitmapContextCreate(NULL, width, height, CGImageGetBitsPerComponent(imageRef), 4 * width, CGImageGetColorSpace(imageRef), alphaInfo);

    CGContextDrawImage(bitmap, CGRectMake(0, 0, width, height), imageRef);

    CGImageRef ref = CGBitmapContextCreateImage(bitmap);
    UIImage *result = [UIImage imageWithCGImage:ref];

    CGContextRelease(bitmap);
    CGImageRelease(ref);

    return result;  
}

问题：如何在不旋转像素的情况下调整从相机中提取的 UIImage 的大小？

4

4 回答 4

61

您的代码不起作用的原因是因为您拥有的代码上的 imageOrientation 没有被考虑在内。具体来说，如果 imageOrientation 是右/左，那么您需要旋转图像并交换宽度/高度。这是一些执行此操作的代码：

-(UIImage*)imageByScalingToSize:(CGSize)targetSize
{
    UIImage* sourceImage = self; 
    CGFloat targetWidth = targetSize.width;
    CGFloat targetHeight = targetSize.height;

    CGImageRef imageRef = [sourceImage CGImage];
    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
    CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);

    if (bitmapInfo == kCGImageAlphaNone) {
        bitmapInfo = kCGImageAlphaNoneSkipLast;
    }

    CGContextRef bitmap;

    if (sourceImage.imageOrientation == UIImageOrientationUp || sourceImage.imageOrientation == UIImageOrientationDown) {
        bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

    } else {
        bitmap = CGBitmapContextCreate(NULL, targetHeight, targetWidth, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

    }   

    if (sourceImage.imageOrientation == UIImageOrientationLeft) {
        CGContextRotateCTM (bitmap, radians(90));
        CGContextTranslateCTM (bitmap, 0, -targetHeight);

    } else if (sourceImage.imageOrientation == UIImageOrientationRight) {
        CGContextRotateCTM (bitmap, radians(-90));
        CGContextTranslateCTM (bitmap, -targetWidth, 0);

    } else if (sourceImage.imageOrientation == UIImageOrientationUp) {
        // NOTHING
    } else if (sourceImage.imageOrientation == UIImageOrientationDown) {
        CGContextTranslateCTM (bitmap, targetWidth, targetHeight);
        CGContextRotateCTM (bitmap, radians(-180.));
    }

    CGContextDrawImage(bitmap, CGRectMake(0, 0, targetWidth, targetHeight), imageRef);
    CGImageRef ref = CGBitmapContextCreateImage(bitmap);
    UIImage* newImage = [UIImage imageWithCGImage:ref];

    CGContextRelease(bitmap);
    CGImageRelease(ref);

    return newImage; 
}

这将调整您的图像大小并将其旋转到正确的方向。如果您需要弧度的定义，它是：

static inline double radians (double degrees) {return degrees * M_PI/180;}

Daniel 给出的答案也是正确的，但它存在线程安全的问题，因为您使用的是 UIGraphicsBeginImageContext()。由于上面的代码只使用了 CG 函数，所以你已经准备好了。我也有一个类似的功能来调整图像大小和对图像进行适当的方面填充 - 如果这就是你要找的，请告诉我。

注意：我从这篇文章中获得了原始功能，并进行了一些修改以使其适用于 JPEG。

于 2009-08-11T19:23:40.317 回答
12

我的一些代码也有这个问题，我发现这个代码有效，检查一下，让我知道你发现了什么

+ (UIImage*)imageWithImage:(UIImage*)image 
               scaledToSize:(CGSize)newSize;
{
   UIGraphicsBeginImageContext( newSize );
   [image drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
   UIImage* newImage = UIGraphicsGetImageFromCurrentImageContext();
   UIGraphicsEndImageContext();

   return newImage;
}
于 2009-08-11T13:14:11.823 回答
2

斯威夫特 3

我将它添加到didFinishPickingMediaWithInfo方法中，然后使用image而不用担心它的旋转。

var image = info[UIImagePickerControllerOriginalImage] as! UIImage
if (image.imageOrientation != .up) {
  UIGraphicsBeginImageContextWithOptions(image.size, false, image.scale)
  image.draw(in: CGRect(x: 0, y: 0, width: image.size.width, height: image.size.height))
  image = UIGraphicsGetImageFromCurrentImageContext()!
  UIGraphicsEndImageContext()
}
于 2016-12-29T14:11:57.770 回答
1

如果您想通过在两侧按宽度或高度裁剪矩形图像（无论是水平还是垂直）制作方形图像，请使用我的代码。不同的是我不拉伸，但我裁剪。我通过修改从顶部代码中制作了它：

//Cropping _image to fit it to the square by height or width

CGFloat a = _image.size.height;
CGFloat b = _image.size.width;
CGRect cropRect;

if (!(a==b)) {
    if (a<b) {
        cropRect = CGRectMake((b-a)/2.0, 0, a, a);
        b = a;
    }
    else if (b<a) {
        cropRect = CGRectMake(0, (a-b)/2.0, b, b);
        a = b;
    }

    CGImageRef imageRef = CGImageCreateWithImageInRect([_image CGImage], cropRect);

    UIImage* sourceImage = _image; 
    CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);
    CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);
    CGContextRef bitmap;
    if (sourceImage.imageOrientation == UIImageOrientationUp || sourceImage.imageOrientation == UIImageOrientationDown) {
        bitmap = CGBitmapContextCreate(NULL, a, a, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

    } else {
        bitmap = CGBitmapContextCreate(NULL, a, a, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);
    }

    if (sourceImage.imageOrientation == UIImageOrientationLeft) {
        CGContextRotateCTM (bitmap, radians(90));
        CGContextTranslateCTM (bitmap, 0, -a);

    } else if (sourceImage.imageOrientation == UIImageOrientationRight) {
        CGContextRotateCTM (bitmap, radians(-90));
        CGContextTranslateCTM (bitmap, -a, 0);

    } else if (sourceImage.imageOrientation == UIImageOrientationUp) {
        // NOTHING
    } else if (sourceImage.imageOrientation == UIImageOrientationDown) {
        CGContextTranslateCTM (bitmap, a, a);
        CGContextRotateCTM (bitmap, radians(-180.));
    }

    CGContextDrawImage(bitmap, CGRectMake(0, 0, a, a), imageRef);
    CGImageRef ref = CGBitmapContextCreateImage(bitmap);
    _image = [UIImage imageWithCGImage:ref];
    CGImageRelease(imageRef);
}
于 2012-05-26T16:43:17.057 回答