Question

我想让用户拍照，然后显示灰度版本。但是，它非常慢，因为图像文件太大/分辨率太高。

当用户拍照时，如何降低图像质量？

下面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 */
}

Answer 1

如果您使用AVFoundation捕获图像，您可以通过更改捕获会话预设来设置要捕获的图像的质量，如下所示：

AVCaptureSession *session = [[AVCaptureSession alloc] init];
session.sessionPreset = AVCaptureSessionPresetLow;

有一个表格与AVFoundation Programming Guide中的哪个分辨率相对应。

Answer 2

如何在将UIImage传递给灰度转换之前对其进行下采样？类似的东西：

NSData *imageAsData = UIImageJPEGRepresentation(imageFromCamera, 0.5);
UIImage *downsampledImaged = [UIImage imageWithData:imageAsData];

当然，您可以使用0.5以外的其他压缩质量。

iOS：拍摄低质量图像

2 个答案: