Question

我有这个代码，它主要使用C代码检查像素颜色：

- (NSArray *)colorsForPixelsAtPoints:(NSArray *)pointValues
{
    NSMutableArray *colors = [NSMutableArray array];
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    // Pinpoint individual pixels from the drawn view.
    for (NSValue *pointValue in pointValues)
    {
        // Setup variables
        unsigned char pixelData[4] = {0, 0, 0, 0};

        CGSize imageSize = self.size;
        CGPoint point = [pointValue CGPointValue];

        // Create graphics context
        CGContextRef colorContext = CGBitmapContextCreate(pixelData, 1, 1, 8, 4, colorSpace, (CGBitmapInfo)kCGImageAlphaPremultipliedLast);
        CGContextSetBlendMode(colorContext, kCGBlendModeCopy);
        CGContextTranslateCTM(colorContext, -point.x, (point.y - imageSize.height));

        // Draw image
        CGRect colorFrame = CGRectMake(0, 0, imageSize.width, imageSize.height);
        CGContextDrawImage(colorContext, colorFrame, [self CGImage]);

        // Get color information
        UIColor *pixelColor = [UIColor colorWithRed: (pixelData[0] / 255.0)
                                              green: (pixelData[1] / 255.0)
                                               blue: (pixelData[2] / 255.0)
                                              alpha: 1];
        [colors addObject: pixelColor];

        // Clean up
        CGContextRelease(colorContext);
    }

    // Clean up
    CGColorSpaceRelease(colorSpace);
    return colors;
}

我想优化所需的时间。

我目前想知道将CGBitmapContextCreate行移到for循环之前，以及如何使其工作。

任何其他加快这一点的想法都会受到赞赏。

Answer 1

请参阅：How to get pixel data from a UIImage (Cocoa Touch) or CGImage (Core Graphics)?

您可以更改方法以读取不同坐标处的像素，而不是读取多个连续像素：

...
// Now your rawData contains the image data in the RGBA8888 pixel format.
for (int ii = 0 ; ii < [pointValues count] ; ++ii)
{
    NSValue *pointValue = [pointValues objectAtIndex:ii]
    CGPoint point = [pointValue CGPointValue];
    int byteIndex = (bytesPerRow * point.y) + point.x * bytesPerPixel;
    CGFloat red   = (rawData[byteIndex]     * 1.0) / 255.0;
    CGFloat green = (rawData[byteIndex + 1] * 1.0) / 255.0;
    CGFloat blue  = (rawData[byteIndex + 2] * 1.0) / 255.0;
    CGFloat alpha = (rawData[byteIndex + 3] * 1.0) / 255.0;

    UIColor *acolor = [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
    [result addObject:acolor];
}
...

还要确保你的点在整数坐标上，否则你可能会遇到奇怪的结果！

加快检查点的像素颜色

1 个答案: