PseudoIsochromatic Plates

Also PIPs; A type of Colorblindness Test where images (shapes, numbers, letters, etc.) are hidden in an image where the foreground and background are Colors of Confusion. They are therefore visible to Color Normals but not to Individuals with the type of CVD to which the plate is tuned. Generally, there is some chromatic and luminance based noise introduced into the picture to make sure the Colorblind can’t use Brightness Cues to identify the image.

There are several different types of plates, as outlined by Ishihara:

• Demonstration Plates – Plates that use colors that are distinguishable to all subjects, including monochromats. They are included to show the subjects what should be expected during the test.
• Vanishing Plates – Only Color Normals will see the image. Colorblind subjects will see nothing. This is the classic type.
  • Tracing Plates – Generally a subset of Vanishing Plates, where only color normal subjects see the path. These are offered as an alternative to plates with numeral/letter based images that are illegible to the illiterate or young children. The subject must trace their finger or a brush over a colored path within the plate.
• Hidden Plates – Only Colorblind Subjects will see the image. Color Normal subjects will see a mess of colorful noise. See also Reverse Ishihara for more info.
• Transformation Plates – Both color normal and colorblind subjects will see images, but the images will be different.

The Ishihara test is the most famous PIP Test. Other examples include:

• The EnChroma online test (link)
• The Colorlite online test (link)
• HRR (Hardy-Rand-Rittler)
• AO Pseudoisochromatic Plates (An amalgamation of Stilling and Ishihara plates)
• SPP2 (Standard Pseudoisochromatic Plate)
• Dvorine
• Bostrom & Kugelberg
• Stilling (defunct)