如何为GPUImage滤镜和视网膜显示设置正确的比例因子？

Question

我在带有视网膜显示屏的iPad上尝试GPUImage filter from this example。

最终图像比必要的图像大2倍。我想我必须设置正确的大小或比例因子，但是如何？

- (void)addBorder {
    if (currentBorder != kBorderInitialValue) {
        GPUImageAlphaBlendFilter *blendFilter = [[GPUImageAlphaBlendFilter alloc] init];
        GPUImagePicture *imageToProcess = [[GPUImagePicture alloc] initWithImage:self.imageToWorkWithView.image];
        GPUImagePicture *border = [[GPUImagePicture alloc] initWithImage:self.imageBorder];

        blendFilter.mix = 1.0f;
        [imageToProcess addTarget:blendFilter];
        [border addTarget:blendFilter];

        [imageToProcess processImage];
        [border processImage];
        self.imageToWorkWithView.image = [blendFilter imageFromCurrentlyProcessedOutput];

        [blendFilter release];
        [imageToProcess release];
        [border release];
    }
}

Answer 1

您可以使用[blendFilter forceProcessingAtSize:]直接设置GPUImageFilter的输出大小。

Answer 2

我找到了一个解决方案，虽然这是一个黑客攻击。

在GPUImageOutput中，添加：

- (UIImage *)imageFromCurrentlyProcessedOutputWithOrientation:(UIImageOrientation)imageOrientation scale:(CGFloat)scale { // Added by Franz
    CGImageRef cgImageFromBytes = [self newCGImageFromCurrentlyProcessedOutputWithOrientation:imageOrientation];
    UIImage *finalImage = [UIImage imageWithCGImage:cgImageFromBytes scale:scale orientation:imageOrientation];
    CGImageRelease(cgImageFromBytes);

    return finalImage;
}
- (UIImage *)imageFromCurrentlyProcessedOutputWithOrientation:(UIImageOrientation)imageOrientation;
{
    return [self imageFromCurrentlyProcessedOutputWithOrientation:imageOrientation scale:1];
}

然后，您可以获得具有指定比例因子的视网膜显示图像。用法示例：

UIImage *filteredImage = [filter imageFromCurrentlyProcessedOutputWithOrientation:sourceImage.imageOrientation scale:sourceImage.scale];

我可以想象有一种更简单的方法。