When you have the brush tool selected, pressing the number keys will adjust the brush opacity.

当你已经选择了画笔工具，按下数字键可以调整画笔的不透明度。

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Once we get the general area of our clouds, we want to drop the brush opacity to 20% and start slowly painting away our detailed areas.

一旦我们得到了云彩的大概区域，要将画笔不透明度调为20%，然后开始慢慢地擦除区域中不需要的细节。

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Select all of them, then with a 20% Opacity, soft brush, paint some highlights on them.

选择全部方块，然后使用不透明度20%的软画笔在上面涂抹一些高光。

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