Some embodiments provide an image editing application that edits an image. The image editing application assigns a mask value to each pixel of the image that includes several pixels. The mask value for a pixel is for using when processing the pixel. The image editing application displays the image in a display area. The image editing application receives several user inputs on a set of pixels of the image. The image editing application incrementally applies an image processing operation to the set of pixels by changing the mask values for the set of pixels each time the set of pixels receives a user input.