Just My Life & My Work

flat、Gouraud、Phong Shading的差別 (Comparison flat, Gouraud, Phong shading)

2011 年 11 月 01 日

現今多邊形的著色方法基本的有這三種：flat、Gouraud、Phong Shading，它們之間有何差別呢？喜歡玩遊戲的人一定要知道Gouraud Shading，這是PC最常使用的著色法，因為效能好、效果還不錯。而近年來，隨著GPU快速的發展，Phong Shading逐漸應用在更真實的著色上。

從一張圖可以看出他們的各自的特色：（a: Flat→b: Gouraud→c: Phong）

從古早到現代：Flat→Gouraud→Phong Shading。

從簡單到複雜：Flat→Gouraud→Phong Shading。

觀察三者所呈現的效果，可以歸納出下列結論：

  • flat shading: constant surface shading
  • Gouraud shading: color interpolation shading
  • Phong shading: vertex normal interpolation shading

用簡單的中文來解釋原理：

  • flat shading：三角形的頂點沒有法向量，三角形整個面才有法向量，打光時整個三角形只呈現一種顏色。
  • Gouraud shading：三角形的頂點都有各自的法向量，打光時三個頂點有各自的顏色，接著做雙線性內插（bilinear interpolation）來求得顏色，使整個三角形有漸層的顏色變化。
  • Phong shading：三角形的頂點都有各自的法向量，先對三角形整個面作法向量的雙線性內插，接著打光來求整個三角形的顏色。

然後我們來分析各自的複雜度：

假設三角形面積為A。三角形個數為N。而且我們知道打一次光需要6次乘法和2次加法和1次查表的運算，此設定為L。雙線性內插設定為B。

  • flat shading的複雜度：N * L
  • Gouraud shading 的複雜度：N * (3 * L + b * A)
  • Phong shading的複雜度：(B + L) * N * A

數學好的人很容易計算出複雜度：Flat<Gouraud<Phong Shading。這裡也因此說明了為何早期電腦都只支援Gouraud shading，就算已經知道Phong shading的效果比Gouraud shading好，但還是選擇效能好而效果不錯的Gouraud shading！如今GPU發展迅速，Phong Shading的效能已得到提昇。

參考：flat shading、Gouraud shading、Phong shading。

分類：

計算機圖學, 課業

9 Comments

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Comments on: "flat、Gouraud、Phong Shading的差別 (Comparison flat, Gouraud, Phong shading)" (9)

  1. 匿名 said:
    2019 年 07 月 13 日 於 22:04:47

    Funny, the first image (comparison) if from my prof 😉

    讚

  2. ChungFu Huang said:
    2015 年 01 月 19 日 於 18:05:41

    你也有再寫OpenGL ?

    讚

  3. seong ping said:
    2013 年 12 月 02 日 於 16:16:17

    Hi HappyMan,

    i find your blog very interesting. i’m working with blender, but i am not sure whether smooth shading in blender actually implements Gouraud or Phong. do you know it?

    many thanks!

    讚

    • HappyMan said:
      2013 年 12 月 02 日 於 23:36:47

      Hi Seong Ping:

      I think it implements both.
      You may refer to [Blender] 鏡射光著色器 (Specular Shader) of my article.

      Although it just displays Phong and the other four kind. Since it implements complex one (Phong), Blender should implement the simple one. 🙂

      讚

      • seong ping said:
        2013 年 12 月 03 日 於 10:01:23

        thanks for your quick response, appreciate it. but what i meant is this: http://wiki.blender.org/index.php/Doc:2.6/Manual/Modeling/Meshes/Smoothing

        there are options of “Smooth" and “Flat" in Shading. i just couldn’t find any description to tell whether the “Smooth" option implements Gouraud or Phong interpolation… do you know it?

        many thanks for your kind help. 🙂

        p/s: i can read Chinese. please feel free to reply in Chinese. i just have no Chinese input in my linux PC..

        讚

        • HappyMan said:
          2013 年 12 月 03 日 於 22:54:20

          In fact, I have the same question that time, but I still have no idea which way Blender implemets the smooth shading.
          I think it is good method to find out the solution by using less triangle. To observe the light reflects on the object. 😉
          Are you a Taiwanese? And live in Taiwan? I live Taipei now. 😀

          讚

          • seong ping said:
            2013 年 12 月 04 日 於 09:54:42

            i guess it is not a concern when material and texture are considered. i’m not in this area..

            thanks for your help anyway. 🙂 i’m a malaysian currently based in singapore. but i once studied in taipei.

            讚

          • HappyMan said:
            2013 年 12 月 04 日 於 10:44:14

            It is good to hear you are a Malaysian, You are so lucky to have the chance to study in Taipei, and work in Singapore. Maybe one day I will achieve the goal that travel along work. 😀
            So may I have your E-mail? Maybe one day in the future we have the opportunity to meet up. 😉

            讚

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