Perceptibility and Acceptability of Gamma Differences of Displayed sRGB Images

摘要

The standard RGB (sRGB) colour space was developed to ensure accurate colour reproduction of images when viewed on Cathode Ray Tube (CRT) displays under specified conditions. Typical display and viewing conditions may vary, however, especially when accessing on-line images. Previous work has been carried out on the effects of different display white points and phosphor chromaticities and on modeling gamma tolerances and display conditions for the sRGB colour space. The work described in this paper investigates the effects of different gamma values on viewing sRGB images. Ten images with variable scene content were selected and converted to the sRGB colour space. A set of test images was generated for each scene by adjusting the display gamma of the sRGB image to a value in the range 1.8 to 2.6. Comparative judgments were conducted in which the reference sRGB image (calibrated for displays with gamma equal to 2.2) in each set was compared to each of the images adjusted to different display gammas. Each pair of images was displayed on the same monitor using software specially developed for the purpose. In the first series, the observers' responses concerned the perceptible difference between the reference sRGB image and the images calibrated to the different gamma value. In the second test their response concerned the acceptable gamma difference. The experimental results were evaluated and discussed. Conclusions were drawn regarding the effects of gamma differences on perceived image quality while viewing on-line sRGB images.