File > Export > Canvas Image/Mask Layer

Exports the active image layer as an image file.

Exporting an image or mask layer exports a file of the same pixel dimensions as the image plane. To see the image plane’s dimensions, choose Edit > Sketch Properties from the Paint Layer Editor.

Export Image/Mask Layer Options

File Type: The file format to save the exported image as: JPEG, TIFF, or 32 bit BMP.
Limit Image Size: When this option is checked, two sliders appear to adjust the Horizontal and Vertical size of the image in pixels. The sliders initially represent the maximum dimensions of the image. If the image exceeds either the horizontal of vertical maximum, it is scaled down, while preserving the aspect ratio, to fit within the specified dimensions.
Quality Level: This option only appears when the File Type is jpeg.

Use the pull-down menu (Maximum, High, Medium or Low) or the slider (values from 1 to 100) to adjust the quality of the jpeg image. A higher quality will result in a larger file size.