将索引颜色.png转换为 RGB 或灰度

Question

我正在编写这个需要显示图像的今日小部件。我注意到，每次加载小部件时，都会重新绘制图像。这大约需要半秒钟。经过一番调查，我发现罪魁祸首是图像文件位于索引颜色空间中。所以：我的问题是：如何将此文件转换为 iPhone 可以更有效地显示的内容？例如，RGB 文件。然后，我会将其保存到一个新文件中，并将该新文件加载到我的 UIImageView 中。

我玩了一下CGImage，因为我相信这是解决方案的方向，但我最终得到了一个白色的UIImageView。

这是我的代码：

UIImage * theCartoon = [UIImage imageWithData:imageData];
    CGImageRef si = [theCartoon CGImage];
    CGDataProviderRef src = CGImageGetDataProvider(si);
    CGImageRef imageRef = CGImageCreateWithPNGDataProvider(src, NULL, NO, kCGRenderingIntentDefault);
    cartoon.image = [[UIImage alloc] initWithCGImage:imageRef];

对这种方法有什么建议吗？一些明显的编程错误？

Answer 1

试试这个

// The source image
CGImageRef image = theCartoon.CGImage;
CGSize size = CGSizeMake(CGImageGetWidth(image), CGImageGetHeight(image));
// The result image in RGB color space   
CGImageRef result = nil;
// Check color space
CGColorSpaceRef srcColorSpace = CGImageGetColorSpace(image);
if (CGColorSpaceGetModel(srcColorSpace) != kCGColorSpaceModelRGB) {
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(nil, size.width, size.height, 8, 0, colorSpace, kCGImageAlphaNoneSkipLast);
    CGRect rect = {CGPointZero, size};
    CGContextDrawImage(context, rect, image);
    result = CGBitmapContextCreateImage(context);
    CGContextRelease(context);
    CGColorSpaceRelease(colorSpace);
}

Answer 2

自从提出这个问题以来已经有一段时间了，但对于可能需要这个的其他人，这是我的解决方案：

-(UIImage *) convertIndexedColorSpaceToRGB:(UIImage *) sourceImage {
CGImageRef originalImageRef = sourceImage.CGImage;
const CGBitmapInfo originalBitmapInfo = CGImageGetBitmapInfo(originalImageRef);
// See: http://stackoverflow.com/questions/23723564/which-cgimagealphainfo-should-we-use
const uint32_t alphaInfo = (originalBitmapInfo & kCGBitmapAlphaInfoMask);
CGBitmapInfo bitmapInfo = originalBitmapInfo;
switch (alphaInfo)
{
    case kCGImageAlphaNone:
        bitmapInfo |= kCGBitmapByteOrder32Big | kCGImageAlphaNoneSkipLast;
        break;
    case kCGImageAlphaPremultipliedFirst:
    case kCGImageAlphaPremultipliedLast:
    case kCGImageAlphaNoneSkipFirst:
    case kCGImageAlphaNoneSkipLast:
        break;
    case kCGImageAlphaOnly:
    case kCGImageAlphaLast:
    case kCGImageAlphaFirst:
    { 
        return sourceImage;
    }
        break;
}
const CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
const CGSize pixelSize = CGSizeMake(sourceImage.size.width * sourceImage.scale, sourceImage.size.height * sourceImage.scale);
const CGContextRef context = CGBitmapContextCreate(NULL,
                                                   pixelSize.width,
                                                   pixelSize.height,
                                                   CGImageGetBitsPerComponent(originalImageRef),
                                                   pixelSize.width*4,
                                                   colorSpace,
                                                   bitmapInfo
                                                   );
CGColorSpaceRelease(colorSpace);
if (!context) return sourceImage;
const CGRect imageRect = CGRectMake(0, 0, pixelSize.width, pixelSize.height);
UIGraphicsPushContext(context);
// Flip coordinate system. See: http://stackoverflow.com/questions/506622/cgcontextdrawimage-draws-image-upside-down-when-passed-uiimage-cgimage
CGContextTranslateCTM(context, 0, pixelSize.height);
CGContextScaleCTM(context, 1.0, -1.0);
[sourceImage drawInRect:imageRect];
UIGraphicsPopContext();
const CGImageRef decompressedImageRef = CGBitmapContextCreateImage(context);
CGContextRelease(context);
UIImage *image = [UIImage imageWithCGImage:decompressedImageRef scale:[UIScreen mainScreen].scale orientation:UIImageOrientationUp];
CGImageRelease(decompressedImageRef);
return image; }