Abstract
Purpose :
When an astigmatic eye or an eye with large higher-order aberrations views a letter, the retinal image is asymmetrically blurred except for the minimum circle of confusion, which may differ depending on the letter type. Therefore, we analyzed the extent to which the feature values of letters differ depending on the typeface and capitalization of the letter, and the effects of these differences on the retinal image.
Methods :
For the feature analysis of characters, the Histograms of Oriented Gradients (HOG) feature analysis method was applied to represent the gradient direction of pixel values as a histogram. The x-directional difference and y-directional difference of adjacent pixels were calculated, and the gradient intensity and gradient direction were calculated from the resulting difference image. Vertical direction components, diagonal direction components, and vertical direction components were divided into vertical direction components, and histograms were calculated with gradient direction as a class and gradient intensity as a frequency. The highest value among the directional components was set at 1.00, and the ratio was calculated. Using the optical design software ZEMAX, an astigmatic eye and an eye with higher order aberrations were created based on the Liou & Brennan model eye, and the effect on the retinal image was confirmed.
Results :
In the vertical, diagonal, and horizontal components, the values were 1.00, 0.78, and 0.46 for lowercase alphabetic MS Gothic and 1.00, 0.75, and 0.60 for uppercase alphabetic Gothic. For lower-case alphabetic Times New Roman, the values were 1.00, 0.92, and 0.70; and for uppercase alphabetic Times New Roman, the values were 1.00, 0.95, and 0.83. For Japanese Hiragana MS Gothic, the values were 0.65, 1.00, and 0.64, and for MS Mincho, 0.57, 1.00, and 0.66. In the retinal image simulations, differences in the effect of astigmatism on the letters were observed for different letter types.
Conclusions :
Although each character has its own characteristics, the ratios of horizontal, diagonal, and vertical components differ depending on the type of character. In the alphabet, there is a slight difference in the horizontal component for uppercase and lowercase letters of the same font. The results also suggest that astigmatism and higher order aberrations have different effects on legibility depending on the type of letter.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.