Hello!
Is this what you're looking for?
When an image is imported into decker it's surrounded by a box with a dotted line. At that time you can adjust the brightness with the "J" and "K" keys on your keyboard.
(機械翻訳: 画像をインポートした後、点線のボックスが表示されている間に、キーボードの「J」と「k」を使用して画像の明るさを変更できます。)
If you have other questions, I'm sure the community here would be happy to help.
Good luck with your project!