Why does outlinePass cause my scene background or transparent darken

[linwecan1991]

When I move my mouse into the model to trigger the outlinePass edge highlight, my scene.background color is also changed. Does anyone know what the problem is?
before:

after:

[wutong52209]

Attempt to add：
this.composer.addPass(new ShaderPass(GammaCorrectionShader));

[linwecan1991]

My friend, ths for your help. But it doesn’t work