在 Objective C 问题中从 UIImage 获取 RGB 值颜色

Question

嘿，我有这个问题，需要帮助；这是我的代码，但我不知道为什么当我单击白色时，视图中的颜色会向我发送黑色？？？...一些帮助？

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {

    UITouch *touch = [touches anyObject];

    if ([touch tapCount] == 2) {
        return;
    }
    self.imageTakenView.userInteractionEnabled = true;
    CGPoint lastPoint = [touch locationInView:self.imageTakenView];
    NSLog(@"%f :: ", lastPoint.x);
    NSLog(@"%f :: ", lastPoint.y);
    UIColor *colorPickerColor;
    colorPickerColor = [self getPixelColorAtLocation:lastPoint];

    self.colorPickerView.backgroundColor = colorPickerColor;

}
- (UIColor*) getPixelColorAtLocation:(CGPoint)point {
    UIColor* color = nil;
    CGImageRef inImage = self.imageTaken.CGImage;
    // Create off screen bitmap context to draw the image into. Format ARGB is 4 bytes for each pixel: Alpa, Red, Green, Blue
    CGContextRef cgctx = [self createARGBBitmapContextFromImage:inImage];
    if (cgctx == NULL) { return nil; /* error */ }

    size_t w = CGImageGetWidth(inImage);
    size_t h = CGImageGetHeight(inImage);
    CGRect rect = {{0,0},{w,h}};

    // 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(cgctx, rect, inImage);

    // Now we can get a pointer to the image data associated with the bitmap
    // context.
    unsigned char* data = CGBitmapContextGetData (cgctx);
    if (data != NULL) {
        //offset locates the pixel in the data from x,y.
        //4 for 4 bytes of data per pixel, w is width of one row of data.
        int offset = 4*((w*round(point.y))+round(point.x));     // 4 base
        int alpha =  data[offset];
        int red = data[offset+1];
        int green = data[offset+2];
        int blue = data[offset+3];
        NSLog(@"offset: %i colors: RGB A %i %i %i  %i",offset,red,green,blue,alpha);
        color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:(blue/255.0f) alpha:(alpha/255.0f)];
    }

    // When finished, release the context
    CGContextRelease(cgctx);
    // Free image data memory for the context
    if (data) { free(data); }

    return color;
}

- (CGContextRef) createARGBBitmapContextFromImage:(CGImageRef) inImage {

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

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

    // 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);
    bitmapByteCount     = (bitmapBytesPerRow * pixelsHigh);

    // Use the generic RGB color space.
    colorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB);
    if (colorSpace == NULL)
    {
        fprintf(stderr, "Error allocating color space\n");
        return NULL;
    }

    // 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 (bitmapData,
                                     pixelsWide,
                                     pixelsHigh,
                                     8,      // bits per component
                                     bitmapBytesPerRow,
                                     colorSpace,
                                     kCGImageAlphaPremultipliedFirst);
    if (context == NULL)
    {
        free (bitmapData);
        fprintf (stderr, "Context not created!");
    }

    // Make sure and release colorspace before returning
    CGColorSpaceRelease( colorSpace );

    return context;
}

在图片中，图片的底部出现了一个棕色的视野；当我点击雾的图片时出现这种颜色所以我认为颜色一定是白色或灰色所以......我完全不明白......

截图是使用 iPhone 5S 模拟器 un xcode 7.2 截取的。

谢谢

Answer 1

您应该制作一个与 imageTakenView 属性大小相同的图像的缩放副本，然后使用该副本来检测颜色。这样，您触摸的点的映射将正确发生。

请参阅此答案以缩放图像 - https://*.com/a/2658801/5316422。

确保将图像缩放到 imageTakenView 属性的大小。