Pseudoisochromatic plate design type is recoverable from delivered colour and dot geometry alone
Abstract
Pseudoisochromatic plates fall into design types characterised by Hardy, Rand and Rittler: demonstration, transformation, vanishing and hidden digit. The type governs what a plate measures and is ordinarily read from the test's own documentation. This note asks how much of it can be recovered from the delivered stimulus instead.
Eleven Ishihara-based plates from a currently deployed web-based screener were measured. Fills are declared in the delivered markup and dot geometry was recovered from the SVG path data, giving 7,400 dots; the reported statistic rests on the 420 to 694 figure/ground border pairs found on each plate. Figure and ground were separated by the spatial compactness of each colour class, which succeeds where assignment by dot count fails on six of the eleven plates. Neighbouring figure/ground dot pairs were then tested for alignment with the dichromatic confusion lines in CIE 1931 xy.
Three groups separate on that single quantity. The demonstration plate returns an aligned fraction of 0% on both red-green axes. Transformation and vanishing plates return 37 to 100% for protan and 50 to 85% for deutan, and do not separate from one another, since both types place the figure/ground boundary along a confusion direction. The hidden digit plate returns 27% for protan and 5% for deutan, the inverted arrangement appearing directly in the measurement. Unsupervised recovery of the figure/ground assignment itself was also attempted and fails: recall reaches 100% on ten plates while precision falls to 38 to 63% on the vanishing plates, with no confidence signal distinguishing successes from failures.
Limitations are stated in full in the manuscript: one test, one manufacturer, eleven plates; colours measured as declared in markup rather than as emitted by a display; no observers tested; and three cited works characterised from their abstracts rather than their full texts.
Cite it
Gonzalez, V. (2026). Pseudoisochromatic plate design type is recoverable from delivered colour and dot geometry alone. Zenodo. https://doi.org/10.5281/zenodo.21876790