Legibility (CIE 145:2002 standard)

Legibility (CIE 145:2002 standard) tab gives the relative visual performance of an observer according to different parameters.

With Legibility (CIE 145:2002 standard) tab, you can indicate if a letter selected in a luminance map can be read.

Note: Legibility (CIE 145:2002 standard) tab applies the CIE 145: 2002 The correlation of models for vision and visual performance standard.

Letter Luminance

In Letter luminance box, you can type the luminance value of the letter in cd/m².

Note: If needed, you can click

to select a pixel in the map. If needed, you can click

to clear the previous selection.

Background Luminance

In Background luminance box, you can type the luminance value of the background in Cd/m².

Note: If needed, you can click

to select a pixel in the map. If needed, you can click

to clear the previous selection.

Note: If needed, you can click

to display colorimetric coordinates when using

Note: Current color is related to the letter coordinates described by a black cross on the diagram. Reference color is related to the background coordinates described by a red cross on the diagram. DeltaE indicates colorimetric gap between letter and background. DeltaE value should be higher than 100 to get good legibility. Colorimetric gap between target and background is low message appears when the DeltaE value is inferior to one hundred value using the DeltaE Luv formula. This value is defined to have a good readability of the letter using the MILSTD1472F norm, 5.2.1.5.6.4 paragraph. For more details about colorimetric data, you can view Parameters of Chromaticity Coordinates Tool.

Note: If needed, you can select the Automatic update check box to update luminance each time the luminance map is modified.

Size of the Critical Detail

In Size of the critical detail box, you can set the size of the letter by typing the angle subtended by the critical detail of the letter in minutes of arc.

Note: As an example, critical detail of the letter can be the stroke widths. The CIE regulation recommends measuring the letter height or stroke width.

Note: Size is calculated using the observer position and the map size.

Note: If needed, you can click

to evaluate the size of the critical detail. A line is displayed in the luminance map to adjust the extreme points.

Observer Age

In Observer age box, you can type the age of the observer in years.

Contrast

In Contrast box, you can read the contrast value calculated from the formula recommended by the CIE 145:2002 regulation.

Contrast = (Luminance of the background- Luminance of the letter)/ Luminance of the background

Relative Visual Performance

In Relative visual performance box, you can read the relative visual performance value.

Warning: Relative visual performance is also called RVP.

Relative visual performance is measured using the size of the critical detail and the observer age. The value is between 0 and 1. RVP = 1 is normalized to the performance level of an adult of twenty years old reading critical detail sizes of 4.5 minutes of arc with an average luminance of 1000 cd/m².

Note: The relative visual performance is defined as a proportional measure of visual performance potential expressed in terms of the maximum value achievable.

Curve Options

In Curve options group box, you can select the option to display the Relative visual performance diagram according to the observer age, the background luminance, the letter luminance, the letter size or the contrast.

When selecting Contrast, you can select Background luminance is constant or Letter luminance is constant.

Surface Tool

In Surface tool box, you can click to select a letter using a displayed rectangle in the luminance map.

You must click or to select if your text is in positive or negative contrast.

Note: If needed, you can click Update to compute letter luminance, background luminance and letter size. You can select the Automatic update check box to computed data in real time.