一種較低級別的API的工作很好的參考是Programming With Quartz
下面的一些代碼是基於這本書的例子。
注:這是未經測試的代碼的意思是隻有起點....
- (NSBitmapImageRep*)convertImageRep:(NSBitmapImageRep*)startingImage{
CGImageRef anImage = [startingImage CGImage];
CGContextRef bitmapContext;
CGRect ctxRect;
size_t bytesPerRow, width, height;
width = CGImageGetWidth(anImage);
height = CGImageGetHeight(anImage);
ctxRect = CGRectMake(0.0, 0.0, width, height);
bytesPerRow = (width * 4 + 63) & ~63;
bitmapData = calloc(bytesPerRow * height, 1);
bitmapContext = createRGBBitmapContext(width, height, TRUE);
CGContextDrawImage (bitmapContext, ctxRect, anImage);
//Now extract the image from the context
CGImageRef bitmapImage = nil;
bitmapImage = CGBitmapContextCreateImage(bitmapContext);
if(!bitmapImage){
fprintf(stderr, "Couldn't create the image!\n");
return nil;
}
NSBitmapImageRep *newImage = [[NSBitmapImageRep alloc] initWithCGImage:bitmapImage];
return newImage;
}
語境創建功能:
CGContextRef createRGBBitmapContext(size_t width, size_t height, Boolean needsTransparentBitmap)
{
CGContextRef context;
size_t bytesPerRow;
unsigned char *rasterData;
//minimum bytes per row is 4 bytes per sample * number of samples
bytesPerRow = width*4;
//round up to nearest multiple of 16.
bytesPerRow = COMPUTE_BEST_BYTES_PER_ROW(bytesPerRow);
int bitsPerComponent = 2; // to get 256 colors (2xRGBA)
//use function 'calloc' so memory is initialized to 0.
rasterData = calloc(1, bytesPerRow * height);
if(rasterData == NULL){
fprintf(stderr, "Couldn't allocate the needed amount of memory!\n");
return NULL;
}
// uses the generic calibrated RGB color space.
context = CGBitmapContextCreate(rasterData, width, height, bitsPerComponent, bytesPerRow,
CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB),
(needsTransparentBitmap ? kCGImageAlphaPremultipliedFirst :
kCGImageAlphaNoneSkipFirst)
);
if(context == NULL){
free(rasterData);
fprintf(stderr, "Couldn't create the context!\n");
return NULL;
}
//Either clear the rect or paint with opaque white,
if(needsTransparentBitmap){
CGContextClearRect(context, CGRectMake(0, 0, width, height));
}else{
CGContextSaveGState(context);
CGContextSetFillColorWithColor(context, getRGBOpaqueWhiteColor());
CGContextFillRect(context, CGRectMake(0, 0, width, height));
CGContextRestoreGState(context);
}
return context;
}
用法是:
NSBitmapImageRep *startingImage; // assumed to be previously set.
NSBitmapImageRep *endingImageRep = [self convertImageRep:startingImage];
// Write out as data
NSData *outputData = [endingImageRep representationUsingType:NSPNGFileType properties:nil];
// somePath is set elsewhere
[outputData writeToFile:somePath atomically:YES];
8位256色?我希望圖像中不超過256種顏色。如果您的顏色可能超過256種,您可能需要使用pngnq(將其捆綁到您的應用中並使用NSTask運行):http://pngnq.sourceforge.net/ – 2010-03-03 04:31:50
是,256種顏色。我正在尋找類似輸出的東西,使用'-representationUsingType:properties'和'NSGIFFileType',除了輸出一個8位的PNG。 pngnq是一個選項(謝謝),但我希望能夠在不產生任何任務的情況下處理它。 – 2010-03-03 09:43:16