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Natalie McHale

CPSC 4040

Fall 2018

Applying a Limited Color Palette

The Focus

• For the final project I focused on suggestion number two. Suggestion number two was described as a

“Color mapping to a limited image palette. Painters regularly work from a limited palette (i.e. a small set of

premixed colors on their palette) from which they do a painting. Make a program that will accept a limited

palette, and then map colors in an image to appropriate colors from this palette, producing an output image

in the limited palette.”

Input

• For the program input the user has to supply a .txt file into the program with the number of colors they are

choosing for the new color palette and the rgb colors associated with each color.

• The user will also need to provide an input image (specifically a .png) that we apply the limited color

palette to.

• The user can optionally give an output file name at the command line, but if one is not provided we will

provide a new name for them if they wish to write the image to a file.

The Work

• The palette will be applied to an input image using two different methods. The first method is one in which

we look at every single pixel in the input image independently, determine which color from the given

palette is most similar, (calculated based on the distance from each color) and then we change the pixel at

every location. The first method is invoked by the user hitting the ‘p’ or ‘P’ key. The second method is to

consider the error from changing the color. In this method we implement Floyd-Steinburg’s algorithm to

distribute the error to neighboring pixels. This second method is invoked by the user hitting the ‘d’ or ‘D’

key.

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Output

• The newly altered image will be displayed on the screen.

• The user will have the option to write this image to a file with keyboard commands.

• The user can decide to reload the original image and apply a different method with the same color palette

without needing to exit and reload the program.

• Once the user hits either the ‘q’, “Q’, or ‘esc’ key the program will exit.

Examples of Valid .txt Files

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Examples of Method 1 versus Method 2 with Example .txt Files on Multiple Input Images

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Summary of Output Images Overall Characteristics

• (blackandwhite.txt) Instead of seeing big “chunks” of black or white, dithering allows us to disperse the

error and spread the colors in a more effective way to obtain more details in our image.

• (RGBTester.txt) The difference between the two methods are show cased when we allow red, green, and

blue to be the only colors. In the first method we see large “chunks” of color. These “chunks” do not all us

to see details or layers in the images. In the case where we use dithering, we observe layers of the image

and can distinguish between different sections of the image.

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• (pinkpurple.txt) In the pink and purple palette we are able to see the details that we are able to add to the

image with dithering. Without spreading the error to the neighboring pixels we notice big “chunks” of the

same color, which do not help us to see what the image is supposed to be, when we use dithering in this

example, the image is completely transformed and we are able to see virtually all of the details from the

original image.

• (redgreen.txt) In the first example, we are clearly able to see the effect of dithering. We see that instead of

having strict defined color grids, we are able to spread out the color and achieve a smoother transition from

color to color, which helps us to achieve a better replicated image.

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• (neon.txt) In these examples we can clearly see that by allowing the error of the color being passed to

neighbors, we are able to obtain a better overall idea of the image. In the first example we cannot see

anything without dithering, but with dithering we are able to start to see the main “ideas” of the image.

• (pastel.txt) The pastel palette is interesting since we are not able to see as much detail on the dithered

image. This is opposite of what we expect to observe, and more research would be needed to explain this

observation.