A projection device and a projecting method are provided. The projection device includes a controller, a light engine, and a storage device. The storage device stores gamma correction curves and a predetermined amount. The controller receives display information of an image. The display information includes pixel information. The controller is configured to: set gray level regions and determine which gray level region does each pixel information fall into according to a gray level of the pixel information; calculate a pixel amount of the pixel information fallen into each gray level region; and when one of the pixel amount exceeds the predetermined amount, select a selected gamma correction curve from the gamma correction curves and adjust the display information according to the selected gamma correction curve to generate adjusted display information. The light engine is electrically coupled to the controller, receives the adjusted display information, and projects an adjusted image accordingly.