After an adjustment, the screen was set to a uniform background luminance for 100 ms, and then the next stimulus was presented; subjectively, this was experienced as a very brief blink that signaled that the adjustment had been made.
Equations 10 to 12 give Tmin, fmin, and K as functions of local background luminance L. For a background intensity value of 128, given a gamma-corrected display, the corresponding local background luminance is computed as follows: L = L min + 128 L max - L min M g (13).
In this experiment the four levels of background luminance were presented between each experimental trial for 5 seconds (see figure 3a).
Glare can be limited in a simplified way indoors or in working places; for instance, establishing maximum relations between the background luminance and object, for different angles of vision (República Argentina, ley 19.587/72 1972).
Clusters could be broadly divided into those modulated by changes in background luminance and clusters selective for moving spots.
However, the situation changes when considering the G index (equation 1). Figure 11 shows the values calculated for a typical background luminance in daylight condition (Lf = 1000 cd/m2) and night condition ( Lf =1 cd/m2) and different observation distances.
It follows that background luminance may be a valuable tool for investigating imagery and its role in various cognitive and sensory processes.
For example, if the background luminance level is low, the visibility threshold generally has a relatively large value.
By combining band sensitivities, background luminance, and texture masking, Safranek and Johnston [2] measured the JND threshold for each coefficient in a given subband to set the quantization level in a differential pulse code modulation (DPCM) quantizer.
For this study we were interested in how background luminance would attenuate processes associated with imagery.
