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问题描述

我将几个photoshop元素映射到CIFilter,唯一一个我遇到问题的是这个级别调整:

I'm mapping several photoshop elements to CIFilter, the only one I'm having trouble with is this Levels Adjustment:

哪个CI过滤器(或过滤器的组合)可以让我利用16,1.73,239&第一个例子中的39/245或者第二个例子中的31,1.25,255 30/255。我相信这是一种阴影/黑白水平调整。

Which CI Filter (or combination of filters) would let me utilize the 16, 1.73, 239 & 39/245 above in the first example or the 31, 1.25, 255 30/255 in the second example. I believe this is a kind of shadow/black and white level adjustment.

任何帮助表示感谢。

推荐答案

通过调整此页面中的公式:,我相信你可以使用 CIColorMatrix CIGammaAdjust的组合来做到这一点和另一个 CIColorMatrix

By adapting the formula from this page: http://http.developer.nvidia.com/GPUGems/gpugems_ch22.html, I believe you can do this using a combination of CIColorMatrix, CIGammaAdjust and another CIColorMatrix.

让我们调用输入级别 inBlack inGamma inWhite ,输出等级 outBlack outWhite 。请注意,Photoshop颜色介于0到255之间,而CI颜色介于0和1之间,因此您需要将Photoshop值(除了 inGamma !)除以255,然后再将它们放入以下公式。

Let's call the input levels inBlack, inGamma and inWhite respectively, and the output levels outBlack and outWhite. Note that Photoshop color are between 0 and 255 while CI colors are between 0 and 1 so you need to divide the Photoshop values (except inGamma!) by 255 before putting them into the following formulas.

输入映射是 pixel =(inPixel-inBlack)/(inWhite-inBlack),其中意味着你的第一个矩阵将是

The input mapping is pixel = (inPixel-inBlack)/(inWhite-inBlack), which means your first matrix will be

red = [1/(inWhite-inBlack) 0 0 0]
green = [0 1/(inWhite-inBlack) 0 0]
blue = [0 0 1/(inWhite-inBlack) 0]
alpha = [0 0 0 1]
bias = [-inBlack/(inWhite-inBlack), -inBlack/(inWhite-inBlack),-inBlack/(inWhite-inBlack), 0]

然后使用 CIGammaAdjust inGamma 编号应用伽马校正(我必须使用反算 1 / inGamma 进行计算时,也试试!)。

Then you apply gamma correction using CIGammaAdjust and the inGamma number (I had to use the inverse 1/inGamma when doing my calculations, try that too!).

最后输出映射是pixel = gammaCorrectedPixel *(outWhite - outBlack)+ outBlack ,为您提供最终矩阵

Finally the output mapping is pixel = gammaCorrectedPixel * (outWhite - outBlack) + outBlack, giving you the final matrix

red = [(outWhite - outBlack) 0 0 0]
green = [0 (outWhite - outBlack) 0 0]
blue = [0 0 (outWhite - outBlack) 0]
alpha = [0 0 0 1]
bias = [outBlack outBlack outBlack 0]

我实际上并没有尝试使用CoreImage,但计算效果很好!

I haven't actually tried this using CoreImage, but the calculations work out nicely!

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08-31 01:28