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我正在嘗試讀取iPhone攝像頭的中心像素（平均值）的RGB值。這應該幾乎在實時發生。因此我打開一個UIImagePickerController，使用計時器每隔x秒拍攝一張照片。處理圖片是在一個單獨的線程中進行的，因此它在計算RGB值時不會阻止應用程序。我嘗試了幾種方法來訪問拍攝圖像的RGB /像素值，但都存在問題，即它們太慢並導致相機視圖滯後。 我嘗試以下：實時訪問iPhone的攝像頭圖像
- (UIColor *)getAverageColorOfImage:(UIImage*)image {
int pixelCount = kDetectorSize * kDetectorSize;
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * kDetectorSize;
NSUInteger bitsPerComponent = 8;
unsigned char *rawData = malloc(pixelCount * bytesPerPixel);
CGContextRef context = CGBitmapContextCreate(rawData, kDetectorSize, kDetectorSize, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextSetInterpolationQuality(context, kCGInterpolationNone);
NSLog(@"Drawing image");
CGContextDrawImage(context, CGRectMake(0, 0, kDetectorSize, kDetectorSize), [image CGImage]);
NSLog(@"Image drawn");
CGContextRelease(context);
// rawData contains the image data in the RGBA8888 pixel format. Alpha values are ignored
int byteIndex = 0;
CGFloat red = 0.0;
CGFloat green = 0.0;
CGFloat blue = 0.0;
for (int i = 0 ; i < pixelCount; ++i) {
red += rawData[byteIndex];
green += rawData[byteIndex + 1];
blue += rawData[byteIndex + 2];
byteIndex += bytesPerPixel;
}
free(rawData);
return [UIColor colorWithRed:red/pixelCount/255.0 green:green/pixelCount/255.0 blue:blue/pixelCount/255.0 alpha:1.0];
}
kDetectorSize被設置爲6，使得所處理的圖像的尺寸6×6像素。其中一個圖像參數也被裁剪爲6x6像素。緩慢的部分是CGContextDrawImage大約需要500-600ms在我的iPhone 4，我想該行一些替代方案：
UIGraphicsPushContext(context);
[image drawAtPoint:CGPointMake(0.0, 0.0)];
UIGraphicsPopContext();
或
UIGraphicsPushContext(context);
[image drawInRect:CGRectMake(0.0, 0.0, kDetectorSize, kDetectorSize)];
UIGraphicsPopContext();
兩種方法都是上面那樣的慢。圖像大小沒有顯着影響（我認爲它沒有影響）。 有沒有人知道更快的方式來訪問RGB值？
如果線程不會導致攝像機視圖滯後，那也可以。我打電話給我的線程：
- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {
UIImage *image = [info objectForKey:UIImagePickerControllerOriginalImage];
[NSThread detachNewThreadSelector:@selector(pickColorFromImage:) toTarget:self withObject:image];
}
- (void)pickColorFromImage:(UIImage *)image {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
[NSThread setThreadPriority:0.0];
[...cropping the image...]
UIColor *averageColor = [self getAverageColorOfImage:croppedImage];
[self performSelectorOnMainThread:@selector(applyPickedColor:) withObject:averageColor waitUntilDone:NO];
[pool release];
}
感謝您的幫助！