线性光模式的Alpha混合层 [英] Alpha Blending Layers for Linear Light Mode

问题描述

我正在重新创建一些Photoshop混合，并尝试使用线性光照模式。在Photoshop中，您将拥有100％不透明度的背景图层，然后是设置为线性光线作为混合模式的50％不透明顶层。

我找到了有关如何进行线性光线混合的信息，但仅适用于两个图层都处于不透明度100％的情况。

以下是将执行线性光线模式的着色器代码和当图层都处于100％不透明度时，它给出与Photoshop相同的结果：

  #define BlendLinearDodgef BlendAddf 
 #define BlendLinearBurnf BlendSubstractf 
 
 #define BlendAddf（base，blend）min（base + blend，1.0）
 #define BlendSubstractf（base，blend）max（base + blend  -  1.0，0.0）
 
 
 #define BlendLinearLightf（base，blend）（blend <0.5？BlendLinearBurnf（base，（2.0 * blend））：BlendLinearDodgef（base，（2.0 *（blend  -  0.5））））） 
  

我看了 http：//en.wikipedia .org / wiki / Alpha_compositing ，但仍然存在问题。

如何让混合模式适用于半透明图层？

解决方案

您应该阅读 PDF规范，了解如何使用混合模式，当你有100％以外的阿尔法。具体请参见第7.2节基本合成计算。第414页上的公式应该解释你需要什么：

pre code> Cr =（1-as / ar）* Cb +（as / ar）* [（1-ab）* Cs + ab * B（Cb，Cs）]

I'm recreating some Photoshop blending and I'm trying to use Linear Light mode. In Photoshop you'd have a background layer at 100% opacity and then a 50% opacity top layer that is set to Linear Light as the blend mode.

I did find info on how to do the Linear Light blend, but it only works when both layers are at 100% opacity.

Here is the shader code that will do Linear Light mode and it gives the same result as Photoshop when layers are both at 100% opacity:

#define BlendLinearDodgef           BlendAddf
#define BlendLinearBurnf            BlendSubstractf

#define BlendAddf(base, blend)      min(base + blend, 1.0)
#define BlendSubstractf(base, blend)    max(base + blend - 1.0, 0.0)


#define BlendLinearLightf(base, blend)  (blend < 0.5 ? BlendLinearBurnf(base, (2.0 * blend)) : BlendLinearDodgef(base, (2.0 * (blend - 0.5))))

I've looked at http://en.wikipedia.org/wiki/Alpha_compositing but am still having issues.

How can I get the blend mode to work for semi-transparent layers?

解决方案

You should read the PDF spec to learn about how to use blend modes when you have alpha other than 100%. In particular, see section 7.2, "Basic Compositing Computations." The formula on page 414 should explain what you need:

Cr= (1-as/ar) * Cb + (as/ar) * [(1-ab) * Cs + ab * B(Cb,Cs)]

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