保存UIImage爲8位灰度位圖

Question

我想輸出一個8位灰度位圖的UIImage，但我不熟悉圖像處理，所以我在如何做到這一點的損失。我遵循這個stackoverflow後（Objective C - save UIImage as a BMP file）創建一個UIImage類別，它可以成功地生成一個RGB 32位圖像，但我一直無法操縱代碼，讓它以8位灰度輸出它。我試圖獲取這個圖像的原始字節，以傳遞給提供的C庫。

是否有什麼樣的UIImage我想要生成位圖？它可以是每個像素的位數，每個組件的位數和alpha設置？我已經嘗試在沒有alpha的8位UIImage上使用此代碼，並且使用alpha的32位，並且都沒有創建可以由OS X打開的位圖。

我希望有人能幫忙！我一直在敲我的頭幾天！

- (NSData *)bitmapData 
{ 
    NSData   *bitmapData = nil; 
    CGImageRef  image = self.CGImage; 
    CGContextRef context = NULL; 
    CGColorSpaceRef colorSpace; 
    UInt8   *rawData; 

    size_t bitsPerPixel = 8; 
    size_t bitsPerComponent = 8; 
    size_t bytesPerPixel = bitsPerPixel/bitsPerComponent; 

    size_t width = CGImageGetWidth(image); 
    size_t height = CGImageGetHeight(image); 

    size_t bytesPerRow = width * bytesPerPixel; 
    size_t bufferLength = bytesPerRow * height; 

    colorSpace = CGColorSpaceCreateDeviceGray(); 

    if (colorSpace) 
    { 
     // Allocate memory for raw image data 
     rawData = (UInt8 *)calloc(bufferLength, sizeof(UInt8)); 

     if (rawData) 
     { 
      CGBitmapInfo bitmapInfo = (CGBitmapInfo)kCGImageAlphaNone; 
      context = CGBitmapContextCreate(rawData, 
              width, 
              height, 
              bitsPerComponent, 
              bytesPerRow, 
              colorSpace, 
              bitmapInfo); 

      if (context) 
      { 
       CGRect rect = CGRectMake(0, 0, width, height); 

       CGContextTranslateCTM(context, 0, height); 
       CGContextScaleCTM(context, 1.0, -1.0); 
       CGContextDrawImage(context, rect, image); 

       bitmapData = [NSData dataWithBytes:rawData length:bufferLength]; 

       CGContextRelease(context); 
      } 

      free(rawData); 
     } 

     CGColorSpaceRelease(colorSpace); 
    } 

    return bitmapData; 
} 

- (NSData *)bitmapFileHeaderData 
{ 
    CGImageRef image = self.CGImage; 
    UInt32  width = (UInt32)CGImageGetWidth(image); 
    UInt32  height = (UInt32)CGImageGetHeight(image); 

    t_bitmap_header header; 

    header.fileType = 0x4D42; 
    header.fileSize = (height * width) + 54; 
    header.reserved1 = 0; 
    header.reserved2 = 0; 
    header.bitmapOffset = 54; 
    header.headerSize = 40; 
    header.width = width; 
    header.height = height; 
    header.colorPlanes = 1; 
    header.bitsPerPixel = 8; 
    header.compression = 0; 
    header.bitmapSize = height * width; 
    header.horizontalResolution = 0; 
    header.verticalResolution = 0; 
    header.colorsUsed = 0; 
    header.colorsImportant = 0; 

    return [NSData dataWithBytes:&header length:sizeof(t_bitmap_header)]; 
} 

- (NSData *)bitmapDataWithFileHeader 
{ 
    NSMutableData *data = [NSMutableData dataWithData:[self bitmapFileHeaderData]]; 
    [data appendData:[self bitmapData]]; 

    return [NSData dataWithData:data]; 
} 

Answer 1

如果你有沒有Alpha通道一個UIImage，您可以將其轉換爲灰度是這樣的：

- (UIImage *)grayscaleImage:(UIImage *)image { 
    CGRect imageRect = CGRectMake(0, 0, image.size.width, image.size.height); 
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray(); 
    CGContextRef context = CGBitmapContextCreate(nil, image.size.width, image.size.height, 8, 0, colorSpace, (CGBitmapInfo)kCGImageAlphaNone); 
    CGContextDrawImage(context, imageRect, [image CGImage]); 
    CGImageRef imageRef = CGBitmapContextCreateImage(context); 
    UIImage *grayscaleImage = [UIImage imageWithCGImage:imageRef]; 
    CGColorSpaceRelease(colorSpace); 
    CGContextRelease(context); 
    CFRelease(imageRef); 
    return grayscaleImage; 
}