Using the self-developed web-based gamma estimation software, experiments of visual estimating gamma are carried out on CRTs and LCDs through internet in three different view environments of dark, dim and office conditioning. The experimental results show that: 1) Estimation deviation of different subjects is less than 0.13 on CRTs, and less than 0.20 on LCDs respectively; 2) Compared with measured results, average error of estimated gamma is less than 0.07 on CRTs, and less than 0.17 on LCDs respectively; 3) Viewing environments do not effect results of visual estimating gamma; 4) Viewing angle has great influence on estimated gamma of LCDs; 5) The “luminance” and “contrast” setting of display does not effect result of visual estimating gamma.