iOS图片美颜

使用GPUImage做美颜非常方便，内置已经提供了一个GPUImagePicture作为图片输入Filter。

GPUImagePicture的实现方法是读取图片数据，将其写入到GPUImageFramebuffer，是一种非常高效的方案。我的方案是将image转为CMSampleBufferRef，这样就能复用视频的处理代码。转换代码如下

- (CVPixelBufferRef)pixelBufferFromUIImage:(UIImage *)image {
    CGSize frameSize = CGSizeMake(CGImageGetWidth(image.CGImage),CGImageGetHeight(image.CGImage));
    NSDictionary *options =
    [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES],kCVPixelBufferCGImageCompatibilityKey,
     [NSNumber numberWithBool:YES],kCVPixelBufferCGBitmapContextCompatibilityKey,
     [NSDictionary dictionary], (id)kCVPixelBufferIOSurfacePropertiesKey, nil];
    CVPixelBufferRef pxbuffer = NULL;
    int cropWidth = (int)CGImageGetWidth(image.CGImage) & ~15;
    int cropHeight = (int)CGImageGetHeight(image.CGImage) & ~1;
    CVReturn status =
    CVPixelBufferCreate(kCFAllocatorDefault, cropWidth, cropHeight, kCVPixelFormatType_32BGRA, (__bridge CFDictionaryRef)options, &pxbuffer);
    NSParameterAssert(status == kCVReturnSuccess && pxbuffer != NULL);
    CVPixelBufferLockBaseAddress(pxbuffer, 0);
    void *pxdata = CVPixelBufferGetBaseAddress(pxbuffer);
    CGColorSpaceRef rgbColorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef context = CGBitmapContextCreate(pxdata, cropWidth, cropHeight,8, CVPixelBufferGetBytesPerRow(pxbuffer),rgbColorSpace,(CGBitmapInfo)kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst);
    CGContextDrawImage(context, CGRectMake(0, 0, cropWidth, cropHeight), image.CGImage);
    CGColorSpaceRelease(rgbColorSpace);
    CGContextRelease(context);
    CVPixelBufferUnlockBaseAddress(pxbuffer, 0);
    return pxbuffer;
}

有个坑的地方是，在后面处理的时候会遇到CVOpenGLESTextureCacheCreateTextureFromImage返回-6638错误，看了官方文档才找到解决方案 https://developer.apple.com/library/archive/qa/qa1781/_index.html

上效果图

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