我想允许用户拍照,然后显示灰度版本。但是,它很慢,因为图像文件太大/分辨率太高。
用户拍照时如何降低图像质量?
这是我用于转换的代码:
- (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]);
/* changes start here */
// Create bitmap image info from pixel data in current context
CGImageRef grayImage = CGBitmapContextCreateImage(context);
// release the colorspace and graphics context
CGColorSpaceRelease(colorSpace);
CGContextRelease(context);
// make a new alpha-only graphics context
context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, nil, kCGImageAlphaOnly);
// draw image into context with no colorspace
CGContextDrawImage(context, imageRect, [image CGImage]);
// create alpha bitmap mask from current context
CGImageRef mask = CGBitmapContextCreateImage(context);
// release graphics context
CGContextRelease(context);
// make UIImage from grayscale image with alpha mask
UIImage *grayScaleImage = [UIImage imageWithCGImage:CGImageCreateWithMask(grayImage, mask) scale:image.scale orientation:image.imageOrientation];
// release the CG images
CGImageRelease(grayImage);
CGImageRelease(mask);
// return the new grayscale image
return grayScaleImage;
/* changes end here */
}