Experiments and analysis on the resolution requirements for alphanumeric readability

Abstract

Experiments and analysis were used to determine the number of resolvable cycles across an alphanumeric character required for readability. This has serious implications for the resolution needed for a surveillance camera to present a “readable” image to a human. Fourier analysis was used to predict the number of cycles required for readability. Using two-dimensional Fourier transforms, the set of 26 English letters and 10 Arabic numerals was analyzed and classified. This theory is supported by empirical data based on user identification of random English letters and Arabic numerals. The results strongly indicate that accurate readability (defined as 90% correctness or better) can be accomplished with approximately 2.8 cycles across a block letter. This appears to suggest a lower resolution requirement than that generally accepted for unknown target identification. The reason is the limited data set of only 36 alphanumeric characters, of which the observer possesses a priori knowledge. Moreover, the ability to read an alphanumeric is a steep function of the resolution between 2 and 3 cycles per character height. The probability of correct “Reading” can be expressed similarly to that of Detection, Recognition and Identification by using a postscript such as “Read₉₀”.