比较UIImage

Question

如何将图像与另一图像进行比较？

谢谢！

Answer 1

如果你有两个UIImages，你应该从这些物体中获得它们的CGImageRef石英表示。然后创建两个新的位图上下文，由您创建并传入的内存缓冲区支持，每个映像一个。然后使用CGContextDrawImage将图像绘制到位图上下文中。现在，图像的字节都在缓冲区中。然后，您可以手动循环或memcmp来检查差异。

关于创建位图上下文并将其绘制到Apple中的Apple自己的详细说明和示例代码如下：

https://developer.apple.com/library/content/documentation/GraphicsImaging/Conceptual/drawingwithquartz2d/dq_context/dq_context.html

您的不同之处在于您将现有图像绘制到上下文中。使用CGContextDrawImage。

Answer 2

这是我在单元测试中用来比较图像的方法。与其他方法（例如，UIImagePNGRepresentation）不同，即使图像具有不同的色彩空间（例如，RGB和灰度），它也可以工作。

@implementation UIImage (HPIsEqualToImage)

- (BOOL)hp_isEqualToImage:(UIImage*)image
{
    NSData *data = [image hp_normalizedData];
    NSData *originalData = [self hp_normalizedData];
    return [originalData isEqualToData:data];
}

- (NSData*)hp_normalizedData
{
    const CGSize pixelSize = CGSizeMake(self.size.width * self.scale, self.size.height * self.scale);
    UIGraphicsBeginImageContext(pixelSize);
    [self drawInRect:CGRectMake(0, 0, pixelSize.width, pixelSize.height)];
    UIImage *drawnImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return UIImagePNGRepresentation(drawnImage);
}

@end

这不是很有效，所以我建议不要在生产代码中使用它，除非性能不是问题。

Answer 3

这是代码示例

-(NSMutableArray*)getImageBinary:(UIImage*)ImageToCompare
{
    int i = 0;    
    int step = 4;

    CGContextRef context = NULL;
    CGColorSpaceRef colorSpace;
    //void * bitmapData;
    //int bitmapByteCount;
    int bitmapBytesPerRow;

    // Get image width, height. We'll use the entire image.
    size_t pixelsWide = CGImageGetWidth(ImageToCompare.CGImage);
    size_t pixelsHigh = CGImageGetHeight(ImageToCompare.CGImage);

    // Declare the number of bytes per row. Each pixel in the bitmap in this
    // example is represented by 4 bytes; 8 bits each of red, green, blue, and
    // alpha.
    bitmapBytesPerRow = (pixelsWide * 4);
    NSMutableArray *firstImagearray=[[NSMutableArray alloc]init];

    //bitmapByteCount = (bitmapBytesPerRow * pixelsHigh);

    // Use the generic RGB color space.
    colorSpace = CGColorSpaceCreateDeviceRGB();

    if (colorSpace == NULL)
    {
        fprintf(stderr, "Error allocating color space\n");
        return nil;
    }

    // Allocate memory for image data. This is the destination in memory
    // where any drawing to the bitmap context will be rendered.
    //bitmapData = malloc( bitmapByteCount );
    //  if (bitmapData == NULL)
    //  {
    //      fprintf (stderr, "Memory not allocated!");
    //      CGColorSpaceRelease( colorSpace );
    //      return NULL;
    //  }

    // Create the bitmap context. We want pre-multiplied ARGB, 8-bits
    // per component. Regardless of what the source image format is
    // (CMYK, Grayscale, and so on) it will be converted over to the format
    // specified here by CGBitmapContextCreate.
    context = CGBitmapContextCreate (NULL,
                                     pixelsWide,
                                     pixelsHigh,
                                     8,      // bits        per component
                                     bitmapBytesPerRow,
                                     colorSpace,
                                     kCGImageAlphaPremultipliedFirst);

    if (context == NULL)
    {
        //free (bitmapData);
        fprintf (stderr, "Context not created!");
    }

    CGRect rect = {{0,0},{pixelsWide, pixelsHigh}};
    //
    // Draw the image to the bitmap context. Once we draw, the memory
    // allocated for the context for rendering will then contain the
    // raw image data in the specified color space.
    CGContextDrawImage(context, rect, ImageToCompare.CGImage);

    // Make sure and release colorspace before returning
    CGColorSpaceRelease( colorSpace );
    /////**********
    size_t _width = CGImageGetWidth(ImageToCompare.CGImage);
    size_t _height = CGImageGetHeight(ImageToCompare.CGImage);

    unsigned char* data = CGBitmapContextGetData (context);

    if (data != NULL) 
    {
        int max = _width * _height * 4;

        for (i = 0; i < max; i+=step)
        {
            [firstImagearray addObject:[NSNumber numberWithInt:data[i + 0]]];
            [firstImagearray addObject:[NSNumber numberWithInt:data[i + 1]]];
            [firstImagearray addObject:[NSNumber numberWithInt:data[i + 2]]];
            [firstImagearray addObject:[NSNumber numberWithInt:data[i + 3]]];     }
    }

    if (context == NULL)
        // error creating context
    return nil;


    //if (data) { free(data); }
    if (context) {
        CGContextRelease(context);
    }
    return firstImagearray;
}

-(BOOL)Compare:(UIImage*)ImageToCompare secondImage:(UIImage*)secondImage
{
    ImageToCompare=[ImageToCompare  scaleToSize:CGSizeMake(self.appdelegate.ScreenWidth,self.appdelegate.ScreenHeigth)];
    secondImage=[secondImage scaleToSize:CGSizeMake(self.appdelegate.ScreenWidth, self.appdelegate.ScreenHeigth)];

    NSArray *first=[[NSArray alloc] initWithArray:(NSArray *)[self    getImageBinary:ImageToCompare]];
    NSArray *second=[[NSArray alloc] initWithArray:(NSArray *)[self getImageBinary:secondImage]];

    for (int x=0; x<first.count; x++)
    {
        if ([((NSNumber*)[first objectAtIndex:x]) intValue] ==[((NSNumber*)[second objectAtIndex:x]) intValue])
        {

        }
        else
        {
             return NO;
        }
    }
    return YES;
}

Answer 4

更新

基于Skycamelfalling's评论，我验证了在使用UIImage的pngData()方法时，我的单元测试仍然通过，而不是使用图像上下文绘制。更简单！

为了历史的兴趣：这是一个hpique's答案的Swift 4变种。当我需要测试两个UIImages的“相同性”时，它在我的单元测试中对我有用。

fileprivate extension UIImage {
    func makeNormalizedData() -> Data? {
        defer { UIGraphicsEndImageContext() }
        let pixelSize = CGSize(width: size.width * scale, height: size.height * scale)
        UIGraphicsBeginImageContext(pixelSize)
        draw(in: CGRect(origin: CGPoint.zero, size: pixelSize))
        guard let drawnImage = UIGraphicsGetImageFromCurrentImageContext() else { return nil }
        return UIImagePNGRepresentation(drawnImage)
    }
}