A Procedural Method for Generating Pseudoisochromatic Plates in the Browser, and the Calibration Limits of Screen-Based Colour-Vision Screening
Abstract
Background. Pseudoisochromatic plate tests, exemplified by the Ishihara plates, remain the most widely used screen for red-green color vision deficiency. Online reproductions are now abundant, but most reuse a small set of fixed, scanned plate images, and few state clearly what a consumer display can and cannot measure.
Method. This paper specifies Procedural Pseudoisochromatic Plate Generation (PPPG), a method for generating pseudoisochromatic plates entirely in the web browser at run time. A target figure is rendered as a binary mask; a spatial-hash dot-packing routine fills the plate with non-overlapping dots; each dot is colored so that figure and background are constructed to differ predominantly along a red-green or blue-yellow (tritan) confusion direction; and dot lightness is randomized within a shared band on every run so that no designed luminance cue distinguishes figure from ground. No plate is stored as an image, and no two runs are identical.
Limitations. The method's ceiling is not its design but the display. On an uncalibrated, three-primary emissive screen with unknown transfer function and 8-bit-per-channel quantization, the intended chromatic relationships are not the relationships seen; the deficiency is further compounded by observer metamerism, because a match constructed for the standard observer is not guaranteed to hold for the anomalous observer being screened. The method therefore constitutes a screening stimulus generator, not a measurement instrument, and cannot classify deficiency type or grade severity.
Contribution. The contribution is not a new psychophysical model of color vision. It is (1) an openly specified, reproducible stimulus-generation pipeline whose assumptions and implementation are fully inspectable, and which removes the memorization and luminance-cue weaknesses of fixed-image online tests; and (2) an explicit account of the calibration limits that bound any screen-based color screen. No clinical validation study was performed, and none is claimed.
Cite it
Gonzalez, V. (2026). A Procedural Method for Generating Pseudoisochromatic Plates in the Browser, and the Calibration Limits of Screen-Based Colour-Vision Screening. Zenodo. https://doi.org/10.5281/zenodo.21310577