READING PERFORMANCE AND VISUAL COMFORT WITH SCALE TO GRAY COMPARED WITH BLACK-AND-WHITE SCANNED PRINT

A particular problem in the display of scanned text is the fact that, given current technology limitations, images can be scanned at a much higher pixel density than they can be displayed on the monitor. Theref ore one pixel on the monitor must be used to represent a block of pixe ls in the scanned image. Most commonly a reduction algorithm is applie d to the scanned image to produce a set of black and white pixels on t he screen (BW). Another algorithm approach ('scale to grey' or STG) is to display a pixel whose grey scale value is calculated from the mix of white and black pixels in the scanned image. STG produces character s which appear more visible - similar to anti-aliasing which can be us ed for designed text. We tested the effects of BW and STG displayed te xt upon reading performance and visual comfort. Twenty-one subjects pe rformed six 20 min reading trials under different display conditions. These six conditions consisted of three different monitors each with B W and STG. The three monitors were selected to provide different displ ay resolutions. Reading performance was measured as the number of line s read, and symptoms were measured with a questionnaire at the end of each trial. ANOVA analysis showed reading performance to be significan tly related (p < 0.0001) to die monitor and also to the display algori thm (p < 0.0001). Reading performance was better on higher resolution monitors, and for each monitor the performance was better with STG (by 19.9, 7.3 and 4.1% for low to high resolution monitors). The symptom score was significantly related to the display algorithm (p < 0.0032), symptoms were lower with STG. STG text resulted in significantly fast er reading speed and significantly lower symptom scores compared to th e same text displayed in BW. The STG advantages were greatest on monit ors with lower resolution.