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iOS图片裁剪、旋转、格式转换

iOS图片裁剪、旋转、格式转换

在使用 CoreML 对图片进行识别时，有时模型需要接收特定格式的图片，这就需要我们先对图片做好处理，再传递给模型。比如，我在一个识别人脸面部表情的程序中，就需要先裁剪出人脸区域，做成适当大小的灰度图，再交给 MLModel 进行识别。

此篇文章汇总了一些对图片进行处理的函数。

CMSampleBufferRef 转 UIImage

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- (UIImage *)getImageFromSampleBuffer:(CMSampleBufferRef) buffer {
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(buffer);
    CVPixelBufferLockBaseAddress(imageBuffer, 0);
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);
    size_t bytesPerRow = CVPixelBufferGetBytesPerRow(imageBuffer);
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    
    CGContextRef context = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    CGImageRef quartzImage = CGBitmapContextCreateImage(context);
    CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
    UIImage *image = [UIImage imageWithCGImage:quartzImage];
    CGImageRelease(quartzImage);
    return image;
}

CGImageRef 转 CVPixelBufferRef

这个函数中对图像做了一些翻转变化，而且还将图片转为了 8 位的灰度图，请注意色彩空间等地方。

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- (CVPixelBufferRef) pixelBufferFromCGImage: (CGImageRef) image {
    NSDictionary *options = @{
                              (NSString*)kCVPixelBufferCGImageCompatibilityKey : @YES,
                              (NSString*)kCVPixelBufferCGBitmapContextCompatibilityKey : @YES,
                              };
    
    CVPixelBufferRef pxbuffer = NULL;

    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault, CGImageGetWidth(image),
                                          CGImageGetHeight(image), kCVPixelFormatType_OneComponent8, (__bridge CFDictionaryRef) options,
                                          &pxbuffer);
    if (status!=kCVReturnSuccess) {
        NSLog(@"Operation failed");
    }
    NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);
    
    CVPixelBufferLockBaseAddress(pxbuffer, 0);
    void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
    
    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceGray(); //灰度
    CGContextRef context = CGBitmapContextCreate(pxdata, CGImageGetWidth(image),
                                                 CGImageGetHeight(image), 8, CVPixelBufferGetBytesPerRow(pxbuffer), rgbColorSpace,
                                                 kCGImageAlphaNone);

    NSParameterAssert(context);

    CGContextConcatCTM(context, CGAffineTransformMakeRotation(0));
    //CGAffineTransform flipVertical = CGAffineTransformMake( 1, 0, 0, -1, 0, CGImageGetHeight(image) );
    //CGContextConcatCTM(context, flipVertical);
    CGAffineTransform flipHorizontal = CGAffineTransformMake( -1.0, 0.0, 0.0, 1.0, CGImageGetWidth(image), 0.0 );
    CGContextConcatCTM(context, flipHorizontal);
    CGContextDrawImage(context, CGRectMake(0, 0, CGImageGetWidth(image),
                                           CGImageGetHeight(image)), image);
    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);
    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);
    return pxbuffer;
}

CVPixelBufferRef 转 UIImage

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- (UIImage *)imageFromPixelBuffer:(CVPixelBufferRef)pixelBufferRef {
    CVImageBufferRef imageBuffer =  pixelBufferRef;
    
    CVPixelBufferLockBaseAddress(imageBuffer, 0);
    void *baseAddress = CVPixelBufferGetBaseAddress(imageBuffer);
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);
    size_t bufferSize = CVPixelBufferGetDataSize(imageBuffer);
    size_t bytesPerRow = CVPixelBufferGetBytesPerRowOfPlane(imageBuffer, 0);
    
    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL, baseAddress, bufferSize, NULL);
    
    CGImageRef cgImage = CGImageCreate(width, height, 8, 32, bytesPerRow, rgbColorSpace, kCGImageAlphaNoneSkipFirst | kCGBitmapByteOrderDefault, provider, NULL, true, kCGRenderingIntentDefault);
    UIImage *image = [UIImage imageWithCGImage:cgImage];
    CGImageRelease(cgImage);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(rgbColorSpace);
    
    CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
    return image;
}

生成灰度图

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- (UIImage*)grayImage:(UIImage*)sourceImage {
    int width = sourceImage.size.width;
    int height = sourceImage.size.height;
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
    CGContextRef context = CGBitmapContextCreate (nil, width, height,8,0, colorSpace,kCGImageAlphaNone);
    CGColorSpaceRelease(colorSpace);
    if (context ==NULL) {
        return nil;
    }
    CGContextDrawImage(context,CGRectMake(0,0, width, height), sourceImage.CGImage);
    UIImage *grayImage = [UIImage imageWithCGImage:CGBitmapContextCreateImage(context)];
    CGContextRelease(context);
    return grayImage;
}

图片裁剪

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- (UIImage*)getSubImage:(CGRect)rect cgImage:(CGImageRef)cgImage {
    CGImageRef subImageRef = CGImageCreateWithImageInRect(cgImage, rect);
    CGRect smallBounds = CGRectMake(0, 0, CGImageGetWidth(subImageRef), CGImageGetHeight(subImageRef));
    
    UIGraphicsBeginImageContext(smallBounds.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextDrawImage(context, smallBounds, subImageRef);
    UIImage* smallImage = [UIImage imageWithCGImage:subImageRef];
    UIGraphicsEndImageContext();
    CGImageRelease(subImageRef);
    return smallImage;
}

图片旋转

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- (UIImage*)rotateImageWithAngle:(UIImage*)vImg Angle:(CGFloat)vAngle IsExpand:(BOOL)vIsExpand {
    CGSize imgSize = CGSizeMake(vImg.size.width * vImg.scale, vImg.size.height * vImg.scale);
    
    CGSize outputSize = imgSize;
    if (vIsExpand) {
        CGRect rect = CGRectMake(0, 0, imgSize.width, imgSize.height);
        //旋转
        rect = CGRectApplyAffineTransform(rect, CGAffineTransformMakeRotation(vAngle*M_PI/180.0));

        outputSize = CGSizeMake(CGRectGetWidth(rect), CGRectGetHeight(rect));
    }
    
    UIGraphicsBeginImageContext(outputSize);
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    CGContextTranslateCTM(context, outputSize.width / 2, outputSize.height / 2);
    CGContextRotateCTM(context, vAngle*M_PI/180.0);
    CGContextTranslateCTM(context, -imgSize.width / 2, -imgSize.height / 2);
    
    [vImg drawInRect:CGRectMake(0, 0, imgSize.width, imgSize.height)];
    
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return image;
}

CGImageRef 转 CVPixelBufferRef

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- (CVPixelBufferRef) pixelBufferColorfulFromCGImage: (CGImageRef) image
{
    NSDictionary *options = @{
                              (NSString*)kCVPixelBufferCGImageCompatibilityKey : @YES,
                              (NSString*)kCVPixelBufferCGBitmapContextCompatibilityKey : @YES,
                              (NSString*)kCVPixelBufferIOSurfacePropertiesKey: [NSDictionary dictionary]
                              };
    CVPixelBufferRef pxbuffer = NULL;
    
    CGFloat frameWidth = CGImageGetWidth(image);
    CGFloat frameHeight = CGImageGetHeight(image);
    
    CVReturn status = CVPixelBufferCreate(kCFAllocatorDefault,
                                          frameWidth,
                                          frameHeight,
                                          kCVPixelFormatType_32BGRA,
                                          (__bridge CFDictionaryRef) options,
                                          &pxbuffer);
    
    NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);
    
    CVPixelBufferLockBaseAddress(pxbuffer, 0);
    void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
    NSParameterAssert(pxdata != NULL);
    
    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    
    CGContextRef context = CGBitmapContextCreate(pxdata,
                                                 frameWidth,
                                                 frameHeight,
                                                 8,
                                                 CVPixelBufferGetBytesPerRow(pxbuffer),
                                                 rgbColorSpace,
                                                 (CGBitmapInfo)kCGImageAlphaNoneSkipFirst);
    NSParameterAssert(context);
    CGContextConcatCTM(context, CGAffineTransformIdentity);
    CGContextDrawImage(context, CGRectMake(0,
                                           0,
                                           frameWidth,
                                           frameHeight),
                       image);
    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);
    
    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);
    
    return pxbuffer;
}

以上各个函数基本都要操作指针，所以一定要注意手动释放内存，否则会造成非常严重的内存泄漏。

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