对比度阈值，小于该值的像素将不产生散景效果。

The contrast threshold below which pixels will not have bokeh artifacts applied.

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如果您使用该值，将提升渲染性能，因为这样做可以避免生成一些不必要的散景效果。

Performance will be improved if you use this parameter to avoid generating unnecessary bokeh artifacts.

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该值的重要意义在于你通常只想场景中一些高频率地方（即图片中的噪声区域）产生散景效果，否则他们将几乎无法看见。

The significance of this is that you usually only need bokeh shapes in areas of high frequency (ie, cluttered or "noisy" areas of image) since they are otherwise nearly invisible.

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