像素的RGB值，由2个重叠像素组成 [英] RGB value of a pixel, combined from 2 overlaying pixels

问题描述

我正在制作一个带水和土地的GIF动画。陆地部分有海岸，因此在某些情况下水会覆盖这些海岸。但是，我希望海水在水下稍微可见。基本上，想象一个透明的png代表水，而另一个代表有沙子。合并的2个图像可以看作是第三个图像。

I am creating an animated gif with Water and Land. The Land part has shores, so the water will in some cases be overlaying those shores. However, I wish the shores to still be slightly visible underneath the water. Basically, imagine 1 transparent png which represents water, over another that has sand. The 2 images combined can be viewed as a third image.

我的问题是 - 我如何计算新像素的RGB值，基于顶部的RGBA（具有透明度）和底部的RGB值，以模仿自然的外观。

My question is - how would I calculate the RGB value of the new pixels, based on the top ones RGBA (with transparency) and the bottom ones RGB values, to mimic a natural look.

我将自己更改透明度级别以查看最适合我的内容，但我遗漏了一个公式。

I will change the transparency level myself to see what suits me best, but I'm missing a formula.

编辑：
atm我有一个想法 - 取水的透明度水平的百分比，并根据该百分比计算一个新的RGB。对沙子像素执行相同操作，但使用剩余百分比（100-透明度％）

atm I do have 1 idea - take the percentage of the transparency level of the water, and based on that percentage calculate a new RGB. Do the same for the sand pixels, but with the "remaining" percentage (100-transparency%)

ie（为简单起见，部分为％）
（R1，G1，B1,40）（R2，G2，B2）=第一组的40％+第二组的60％

ie (A part is in %, for simplicity) (R1,G1,B1, 40) (R2,G2,B2) = 40% of first group + 60% of second

推荐答案

Alpha混合要么死了简单（alpha是0-255，所以颜色是目标*（255 - a）+覆盖* a，全部超过255）或非常微妙，当你允许目标也有alpha 。此外，有必要为许多应用程序有效地实现，这通过预乘，然后使用

Alpha blending is either dead simple (alpha is on 0-255, so the colour is destination * (255 - a) + overlay * a, all over 255) or quite subtle, when you allow the destination to also have alpha. Also it is necessary to implement efficiently for many applications, which is done by pre-multiplying, then hardcoding the division by 255 using

 ((x+1) * 257) >> 16;

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