Koi are the decorative carp especially popular in Japan and China, and now in many other places as well. I am endlessly fascinated by koi ponds, and cannot recall ever passing by one without taking photos. This leads to a backlog of koi images.

This photo was taken at the koi pond near the entrance of the Mauna Lani hotel on the Big Island of Hawaii.

The color and composition have potential, but the original is a bit blurred. Those fish refuse to hold still even if you asked them politely. It also lacks the dramatic impact that koi might impart.

Posterization is a technique for further punching up photos. The methods reduces the number of colors in a scene by the number of bits in the color components. This produces larger areas of pure color, like a poster painted with a few solid colors.

For the koi image, some experimentation revealed that the image was better with more black in the water. I set the black level to push the dark tones into pure black. In Photoshop™ this is done by selecting Enhance>Adjust Lighting>Levels and moving the lower limit into the histogram of levels.

The next question is how many levels to use in the posterization. Select Filters>Adjustments>Posterize … and set the number of levels. Often it seems that four levels works best. With the koi, however, four levels is too few to give interesting detail:

Increasing to five levels produces a better effect:

After the image is posterized the color saturation and levels can be further adjusted. The koi didn’t require that.