将图像转换成黑白问题CGContext – iPhone Dev

我正在使用一种方法将用相机拍摄的图像转换为黑白图像。 我遇到的问题是，如果图片是以肖像模式拍摄的，它将在下一个视图中旋转和延伸。 但是，如果在风景拍摄，它只是find。

当我将图像转换为黑白色时，我只能复制这个错误。 这是我正在使用的方法。

林不是100％，这个错误是从转换，但它只发生在转换。 哦是的。 这是iOS 4。

/// - (UIImage *)convertImageToGrayScale:(UIImage *)image { // Create image rectangle with current image width/height CGRect imageRect = CGRectMake(0, 0, image.size.width, image.size.height); // Grayscale color space CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray(); // Create bitmap content with current image size and grayscale colorspace CGContextRef context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, colorSpace, kCGImageAlphaNone); // Draw image into current context, with specified rectangle // using previously defined context (with grayscale colorspace) CGContextDrawImage(context, imageRect, [image CGImage]); // Create bitmap image info from pixel data in current context CGImageRef imageRef = CGBitmapContextCreateImage(context); // Create a new UIImage object UIImage *newImage = [UIImage imageWithCGImage:imageRef]; // Release colorspace, context and bitmap information CGColorSpaceRelease(colorSpace); CGContextRelease(context); CFRelease(imageRef); // Return the new grayscale image return newImage; } 

@lessfame

Answer 1

我知道了

我最终做的是find这个function，旋转图像的变换取决于取决于方向。 它所做的是修复这个奇怪的旋转错误。

下面的代码片段：

 - (UIImage *)rotateImage:(UIImage *)image { int kMaxResolution = 320; // Or whatever CGImageRef imgRef = image.CGImage; CGFloat width = CGImageGetWidth(imgRef); CGFloat height = CGImageGetHeight(imgRef); CGAffineTransform transform = CGAffineTransformIdentity; CGRect bounds = CGRectMake(0, 0, width, height); if (width > kMaxResolution || height > kMaxResolution) { CGFloat ratio = width/height; if (ratio > 1) { bounds.size.width = kMaxResolution; bounds.size.height = bounds.size.width / ratio; } else { bounds.size.height = kMaxResolution; bounds.size.width = bounds.size.height * ratio; } } CGFloat scaleRatio = bounds.size.width / width; CGSize imageSize = CGSizeMake(CGImageGetWidth(imgRef), CGImageGetHeight(imgRef)); CGFloat boundHeight; UIImageOrientation orient = image.imageOrientation; switch(orient) { case UIImageOrientationUp: //EXIF = 1 transform = CGAffineTransformIdentity; break; case UIImageOrientationUpMirrored: //EXIF = 2 transform = CGAffineTransformMakeTranslation(imageSize.width, 0.0); transform = CGAffineTransformScale(transform, -1.0, 1.0); break; case UIImageOrientationDown: //EXIF = 3 transform = CGAffineTransformMakeTranslation(imageSize.width, imageSize.height); transform = CGAffineTransformRotate(transform, M_PI); break; case UIImageOrientationDownMirrored: //EXIF = 4 transform = CGAffineTransformMakeTranslation(0.0, imageSize.height); transform = CGAffineTransformScale(transform, 1.0, -1.0); break; case UIImageOrientationLeftMirrored: //EXIF = 5 boundHeight = bounds.size.height; bounds.size.height = bounds.size.width; bounds.size.width = boundHeight; transform = CGAffineTransformMakeTranslation(imageSize.height, imageSize.width); transform = CGAffineTransformScale(transform, -1.0, 1.0); transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0); break; case UIImageOrientationLeft: //EXIF = 6 boundHeight = bounds.size.height; bounds.size.height = bounds.size.width; bounds.size.width = boundHeight; transform = CGAffineTransformMakeTranslation(0.0, imageSize.width); transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0); break; case UIImageOrientationRightMirrored: //EXIF = 7 boundHeight = bounds.size.height; bounds.size.height = bounds.size.width; bounds.size.width = boundHeight; transform = CGAffineTransformMakeScale(-1.0, 1.0); transform = CGAffineTransformRotate(transform, M_PI / 2.0); break; case UIImageOrientationRight: //EXIF = 8 boundHeight = bounds.size.height; bounds.size.height = bounds.size.width; bounds.size.width = boundHeight; transform = CGAffineTransformMakeTranslation(imageSize.height, 0.0); transform = CGAffineTransformRotate(transform, M_PI / 2.0); break; default: [NSException raise:NSInternalInconsistencyException format:@"Invalid image orientation"]; } UIGraphicsBeginImageContext(bounds.size); CGContextRef context = UIGraphicsGetCurrentContext(); if (orient == UIImageOrientationRight || orient == UIImageOrientationLeft) { CGContextScaleCTM(context, -scaleRatio, scaleRatio); CGContextTranslateCTM(context, -height, 0); } else { CGContextScaleCTM(context, scaleRatio, -scaleRatio); CGContextTranslateCTM(context, 0, -height); } CGContextConcatCTM(context, transform); CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, width, height), imgRef); UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); return imageCopy; } 

该方法返回一个IMAGE，然后我可以在我的黑白function中使用

 - (UIImage *)convertImageToGrayScale:(UIImage *)image { image = [self rotateImage:image];//THIS IS WHERE REPAIR THE ROTATION PROBLEM // Create image rectangle with current image width/height CGRect imageRect = CGRectMake(0, 0, image.size.width, image.size.height); // Grayscale color space CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray(); // Create bitmap content with current image size and grayscale colorspace CGContextRef context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, colorSpace, kCGImageAlphaNone); // Draw image into current context, with specified rectangle // using previously defined context (with grayscale colorspace) CGContextDrawImage(context, imageRect, [image CGImage]); // Create bitmap image info from pixel data in current context CGImageRef imageRef = CGBitmapContextCreateImage(context); // Create a new UIImage object UIImage *newImage = [UIImage imageWithCGImage:imageRef]; // Release colorspace, context and bitmap information CGColorSpaceRelease(colorSpace); CGContextRelease(context); CFRelease(imageRef); // Return the new grayscale image return newImage; } 

请享用！

Answer 2

我修改了能够处理2.0缩放图像而不失去分辨率：

 - (UIImage *)convertImageToGrayScale:(UIImage *)image { // Create image rectangle with current image width/height CGRect imageRect = CGRectMake(0, 0, image.scale*image.size.width, image.scale*image.size.height); // Grayscale color space CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray(); // Create bitmap content with current image size and grayscale colorspace CGContextRef context = CGBitmapContextCreate(nil, image.scale*image.size.width, image.scale*image.size.height, 8, 0, colorSpace, kCGImageAlphaNone); // Draw image into current context, with specified rectangle // using previously defined context (with grayscale colorspace) CGContextDrawImage(context, imageRect, [image CGImage]); // Create bitmap image info from pixel data in current context CGImageRef imageRef = CGBitmapContextCreateImage(context); // Create a new UIImage object UIImage *newImage = [UIImage imageWithCGImage:imageRef scale:image.scale orientation:image.imageOrientation]; // Release colorspace, context and bitmap information CGColorSpaceRelease(colorSpace); CGContextRelease(context); CFRelease(imageRef); // Return the new grayscale image return newImage; } 

Answer 3

我想我明白了这一点。 现在去testing。

原来有UIImage方向标志。 我在http://discussions.apple.com/message.jspa?messageID=7276709find了支持主题

我认为这是使用一个开关来检查方向，并基于它将其旋转到正确的方向。

我发现后，我张贴代码。

Stanks！

• @lessfame