Here are quick instructions for using ValuePal. When the app opens, you can access 2 windows by swiping horizontally. You can bring in an image in each window by taking a picture or selecting from photo file. This way you can compare a reference to your work (or palette, or sketch). Tap anywhere to get a greyscale value, 1-10. Number will appear in circle at upper right and value will be highlighted in graphic scale above.
Mapping: Tap any value in the graphic scale at the top of the screen and a ‘map’ will be produced showing a pattern of that value throughout the image. You can add more mapping by tapping additional graphic scale values. This may take a while. Tapping anywhere on the image ends mapping & returns to original image.
Bracketing: Selecting the cube (lower right) lets you convert your image to a 3-value b/w image. Choose a high, medium or low key set (light, medium, dark). Tapping anywhere on the image returns to original image.