【图片旋转】很怪异的问题

码拜

9年 ago

从相册里面拿到一张照片，假如是本人手机上拍的图片，旋转就会出现问题，假如是外部导入的图片，旋转就正确。实在不知道怎么回事。附上旋转的代码。
– (UIImage *)rotatedImage:(UIImage *)imageToRotate withRotion:(NSInteger)rotation
{
CGFloat rotationAngle = rotation * M_PI / 180;
CGSize imageSize = imageToRotate.size;

// Image size after the transformation
CGSize outputSize = [self sizeForRotatedImage:imageToRotate withRotation:rotation];

CGSize absoluteOutputSize = CGSizeAbsolute(outputSize);

UIImage *outputImage = nil;

// Create the bitmap context
UIGraphicsBeginImageContext(absoluteOutputSize);
CGContextRef imageContextRef = UIGraphicsGetCurrentContext();

// Set the anchor point to {0.5, 0.5}
CGContextTranslateCTM(imageContextRef, .5 * absoluteOutputSize.width, .5 * absoluteOutputSize.height);

// Apply rotation
CGContextRotateCTM(imageContextRef, rotationAngle);

// Draw the current image
CGContextScaleCTM(imageContextRef, 1.0, -1.0);
CGContextDrawImage(imageContextRef, (CGRect) {{-(.5 * imageSize.width), -(.5 * imageSize.height)}, imageSize}, imageToRotate.CGImage);

outputImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

return outputImage;
}
– (CGSize)sizeForRotatedImage:(UIImage *)imageToRotate withRotation:(NSInteger)rotation
{
if (imageToRotate == nil) {
return CGSizeMake(0, 0);
}

CGFloat rotationAngle = rotation * M_PI / 180;

CGSize imageSize = imageToRotate.size;
// Image size after the transformation
CGSize outputSize = CGSizeApplyAffineTransform(imageSize, CGAffineTransformMakeRotation(rotationAngle));

return outputSize;
}

图片大小你都设置一样试试，应该是你没有自动识别图片的大小

这是原因是图片是有元数据的，你发现的imageOrientation只是其中元数据的一种，有两种方式处理：
一。在draw的时候判断图片方向
二。把方向数据干掉：

- (UIImage *)fixOrientation:(UIImage *)aImage {
    
    // No-op if the orientation is already correct
    if (aImage.imageOrientation == UIImageOrientationUp) 
        return aImage;
    
    // We need to calculate the proper transformation to make the image upright.
    // We do it in 2 steps: Rotate if Left/Right/Down, and then flip if Mirrored.
    CGAffineTransform transform = CGAffineTransformIdentity;
    
    switch (aImage.imageOrientation) {
        case UIImageOrientationDown:
        case UIImageOrientationDownMirrored:
            transform = CGAffineTransformTranslate(transform, aImage.size.width, aImage.size.height);
            transform = CGAffineTransformRotate(transform, M_PI);
            break;
            
        case UIImageOrientationLeft:
        case UIImageOrientationLeftMirrored:
            transform = CGAffineTransformTranslate(transform, aImage.size.width, 0);
            transform = CGAffineTransformRotate(transform, M_PI_2);
            break;
            
        case UIImageOrientationRight:
        case UIImageOrientationRightMirrored:
            transform = CGAffineTransformTranslate(transform, 0, aImage.size.height);
            transform = CGAffineTransformRotate(transform, -M_PI_2);
            break;
        default:
            break;
    }
    
    switch (aImage.imageOrientation) {
        case UIImageOrientationUpMirrored:
        case UIImageOrientationDownMirrored:
            transform = CGAffineTransformTranslate(transform, aImage.size.width, 0);
            transform = CGAffineTransformScale(transform, -1, 1);
            break;
            
        case UIImageOrientationLeftMirrored:
        case UIImageOrientationRightMirrored:
            transform = CGAffineTransformTranslate(transform, aImage.size.height, 0);
            transform = CGAffineTransformScale(transform, -1, 1);
            break;
        default:
            break;
    }
    
    // Now we draw the underlying CGImage into a new context, applying the transform
    // calculated above.
    CGContextRef ctx = CGBitmapContextCreate(NULL, aImage.size.width, aImage.size.height,
                                             CGImageGetBitsPerComponent(aImage.CGImage), 0,
                                             CGImageGetColorSpace(aImage.CGImage),
                                             CGImageGetBitmapInfo(aImage.CGImage));
    CGContextConcatCTM(ctx, transform);
    switch (aImage.imageOrientation) {
        case UIImageOrientationLeft:
        case UIImageOrientationLeftMirrored:
        case UIImageOrientationRight:
        case UIImageOrientationRightMirrored:
            // Grr...
            CGContextDrawImage(ctx, CGRectMake(0,0,aImage.size.height,aImage.size.width), aImage.CGImage);
            break;
            
        default:
            CGContextDrawImage(ctx, CGRectMake(0,0,aImage.size.width,aImage.size.height), aImage.CGImage);
            break;
    }
    
    // And now we just create a new UIImage from the drawing context
    CGImageRef cgimg = CGBitmapContextCreateImage(ctx);
    UIImage *img = [UIImage imageWithCGImage:cgimg];
    CGContextRelease(ctx);
    CGImageRelease(cgimg);
    return img;
}