|Faint Red||(255,250,250)||(0°, 2%, 100%)|
|Faint Green||(250,255,250)||(120°, 2%, 100%)|
|Color Distance||7.07 units||3.46 units|
|Gray Red||(143,138,138)||(0°, 3.5%, 56.1%)|
|Gray Green||(138,143,138)||(120°, 3.5%, 56.1%)|
|Color Distance||7.07 units||1.94 units|
|The Ishihara color test was designed to identify people with different types of color blindness. A person with full color vision should see numbers embedded in the circles (12, 2, 42, 6, and 74).
Depending on the type of color blindness, some numbers may not be visible. For example, the "74" in the last circle may appear as "71" or "21" if you have dichromatic or trichromatic color blindness, and may not be visible at all if you have achromatic color blindness.
However, even with full color vision, some of these numbers may be difficult to identify. (The "2" and "6" are usually difficult.) By adjusting the colors, minor differences can become easier to see.
Inverting the RGB values can be particularly useful for pulling out fine details in very dark or very light images.
With the normal image, the lightning appears to be bright and blended into a bright border. By inverting the image, the core of each lightning bolt is visible as a sharp edge.
In July 2008, Iran's Sepah News released a photo showing four missiles being launched as part of a test. Close observation identified cloning (copying) of smoke within the picture. The third missile from the left was digitally added.
By altering the image coloring, you can see a faded halo in the sky around the third missile, identifying the alterated area.
(Hue rotated 200°, Saturation increased to 200%, and Brightness decreased to 60%.)
In this example, the altered area around the smoke is very visible by inverting the image. Altering the HSV shows the same region as a slight discoloration, but it extends around the missile.
In some online forums, users may invert or alter colors in pictures. This may anonymize images or make the picture appear different. Color-altered pictures can be easily returned to their source coloring by re-inverting or rotating the hue back to normal.
When colors are altered, it can be difficult to identify what is in the image. Is the person male or female? Is the person well-known or obscure? Are there any distinct features or markings? What color is the clothing? What is in the background?
By inverting the image, this example shows male musician Alice Cooper (photographed by Gage Skidmore, 2013). The inverted source obscures facial features, distorts clothing colors, and makes it difficult to identify the stadium seats in the background.