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. 2005 Jul;89(7):828-30.
doi: 10.1136/bjo.2004.062240.

The effect of digital image resolution and compression on anterior eye imaging

R C Peterson  1 , J S Wolffsohn
Affiliations

The effect of digital image resolution and compression on anterior eye imaging

R C Peterson et al. Br J Ophthalmol. 2005 Jul.

Abstract

Aim: To determine the theoretical and clinical minimum image pixel resolution and maximum compression appropriate for anterior eye image storage.

Methods: Clinical images of the bulbar conjunctiva, palpebral conjunctiva, and corneal staining were taken at the maximum resolution of Nikon:CoolPix990 (2048x1360 pixels), DVC:1312C (1280x811), and JAI:CV-S3200 (767x569) single chip cameras and the JVC:KYF58 (767x569) three chip camera. The images were stored in TIFF format and further copies created with reduced resolution or compressed. The images were then ranked for clarity on a 15 inch monitor (resolution 1280 x 1024) by 20 optometrists and analysed by objective image analysis grading. Theoretical calculation of the resolution necessary to detect the smallest objects of clinical interest was also conducted.

Results: Theoretical calculation suggested that the minimum resolution should be > or = 579 horizontal pixels at 25x magnification. Image quality was perceived subjectively as being reduced when the pixel resolution was lower than 767 x 569 (p<0.005) or the image was compressed as a BMP or <50% quality JPEG (p<0.005). Objective image analysis techniques were less susceptible to changes in image quality, particularly when using colour extraction techniques.

Conclusion: It is appropriate to store anterior eye images at between 1280 x 811 and 767 x 569 pixel resolution and at up to 1:70 JPEG compression.

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Figures

Figure 1
Figure 1
Mean subjective ranking for each camera model’s resolution range. Error bars = 1 SD (n = 20).
Figure 2
Figure 2
Mean subjective ranking for each camera model’s compression range. Error bars = 1 SD (n = 20).
Figure 3
Figure 3
Mean objective edge detection and colouration grading for each camera model’s resolution range. Error bars = 1 SD.
Figure 4
Figure 4
Mean objective edge detection and colouration grading for each camera model’s compression range. Error bars = 1 SD.
See this image and copyright information in PMC

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