这是可能的,我之前尝试过两条路径:
转换为灰度,然后逐像素转换为黑白。
--问题是我在透明图像上没有得到好的结果。
如果您不是很严格,给定 RGBA 图像,获取像素 RGB 平均值并使用提供的阈值转换为黑白并保留其透明度。从技术上讲,这仍然是 RGBA,但更多的是黑色、白色和透明度。
e.g.
UIImage *originalImage = [UIImage imageNamed:@"option_bluetooth.png"];
unsigned char *pixelBuffer = [self getPixelData:originalImage.CGImage];
size_t length = originalImage.size.width * originalImage.size.height * 4;
CGFloat intensity;
int bw;
//50% threshold
const CGFloat THRESHOLD = 0.5;
for (int index = 0; index < length; index += 4)
{
intensity = (pixelBuffer[index] + pixelBuffer[index + 1] + pixelBuffer[index + 2]) / 3. / 255.;
if (intensity > THRESHOLD) {
bw = 255;
} else {
bw = 0;
}
pixelBuffer[index] = bw;
pixelBuffer[index + 1] = bw;
pixelBuffer[index + 2] = bw;
}
CGColorSpaceRef colorSpace=CGColorSpaceCreateDeviceRGB();
CGContextRef bitmapContext=CGBitmapContextCreate(pixelBuffer, originalImage.size.width, originalImage.size.height, 8, 4*originalImage.size.width, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrderDefault);
CFRelease(colorSpace);
free(pixelBuffer);
CGImageRef cgImage=CGBitmapContextCreateImage(bitmapContext);
CGContextRelease(bitmapContext);
UIImage *bwImage = [UIImage imageWithCGImage:cgImage];
我通过写入屏幕外上下文来获取像素数据(苹果建议的获取原始数据的新方法对我不起作用)
e.g.
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = malloc(imageHeight * imageWidth * 4);
CGContextRef offscreenContext = CGBitmapContextCreate(rawData, imageWidth, imageHeight,
bitsPerComponent, bytesPerRow, colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrderDefault);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(offscreenContext, CGRectMake(0, 0, imageWidth, imageHeight), cgCropped);
CGContextRelease(offscreenContext);
这是获取像素数据的代码
+ (unsigned char *) getPixelData: (CGImageRef) cgCropped {
size_t imageWidth = CGImageGetWidth(cgCropped);
size_t imageHeight = CGImageGetHeight(cgCropped);
size_t bitsPerComponent = 8;
size_t bytesPerPixel = 4;
size_t bytesPerRow = bytesPerPixel * imageWidth;
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = malloc(imageHeight * imageWidth * 4);
CGContextRef offscreenContext = CGBitmapContextCreate(rawData, imageWidth, imageHeight,
bitsPerComponent, bytesPerRow, colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrderDefault);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(offscreenContext, CGRectMake(0, 0, imageWidth, imageHeight), cgCropped);
CGContextRelease(offscreenContext);
return rawData;
}