iPhone NSBitmapImageRep

Question

我有一个包含 JPEG 图像数据的缓冲区。我需要在 UIImageView 中显示此图像。我需要将此图像缓冲区转换为 UIImage 对象并按如下方式使用它

NSData *data = [NSData dataWithContentsOfFile:appFile];UIImage *theImage = [[UIImage alloc] initWithData:data];

我显示了图像，但与实际分辨率相比，分辨率较低。我是否需要先将其转换为 Bitmap，然后将其与 UIImage 一起使用？我似乎无法使用 NSBitmapImageRep。关于如何实现这一目标有什么想法吗？

Answer 1

如果 UIImageView 框架尺寸与源图像尺寸不同，您将获得图像的调整大小版本。质量可能相当粗糙，具体取决于执行的转换量。

我在网上某个地方找到了这段代码(对不起原作者 - 我已经失去了归属)，它执行更平滑的调整大小:

UIImage* resizedImage(UIImage *inImage, CGRect thumbRect)
{
    CGImageRef          imageRef = [inImage CGImage];
    CGImageAlphaInfo    alphaInfo = CGImageGetAlphaInfo(imageRef);

    // There's a wierdness with kCGImageAlphaNone and CGBitmapContextCreate
    // see Supported Pixel Formats in the Quartz 2D Programming Guide
    // Creating a Bitmap Graphics Context section
    // only RGB 8 bit images with alpha of kCGImageAlphaNoneSkipFirst, kCGImageAlphaNoneSkipLast, kCGImageAlphaPremultipliedFirst,
    // and kCGImageAlphaPremultipliedLast, with a few other oddball image kinds are supported
    // The images on input here are likely to be png or jpeg files
    if (alphaInfo == kCGImageAlphaNone)
        alphaInfo = kCGImageAlphaNoneSkipLast;

    // Build a bitmap context that's the size of the thumbRect
    CGContextRef bitmap = CGBitmapContextCreate(
                                                NULL,
                                                thumbRect.size.width,       // width
                                                thumbRect.size.height,      // height
                                                CGImageGetBitsPerComponent(imageRef),   // really needs to always be 8
                                                4 * thumbRect.size.width,   // rowbytes
                                                CGImageGetColorSpace(imageRef),
                                                alphaInfo
                                                );

    // Draw into the context, this scales the image
    CGContextDrawImage(bitmap, thumbRect, imageRef);

    // Get an image from the context and a UIImage
    CGImageRef  ref = CGBitmapContextCreateImage(bitmap);
    UIImage*    result = [UIImage imageWithCGImage:ref];

    CGContextRelease(bitmap);   // ok if NULL
    CGImageRelease(ref);

    return result;
}