A test and measurement device is described that has an input for receiving a selected image, a display output, and one or more processors configured to receive a maximum and minimum luminance value related to the selected image, and generate a chromaticity diagram of the image on the display output for only those pixels in the selected image that have luminance values between the maximum and minimum luminance values. The device may also generate a modified image from the selected image in which pixels from the selected image that fall within the maximum and minimum luminance value are reproduced in the modified image without modification and other pixels not within the maximum and minimum luminance value are modified. Methods are also described.