Tham khảo tài liệu 'vision systems - applications part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 3D Cameras 3D Computer Vision of wide Scope 191 adjusted for all pixel elements together one might guess that it is the best strategy to avoid each pixel from oversaturation. Focusing the small object will most likely decrease the accuracy for the remaining scene. This also means that the signal level for objects with low diffuse reflectivity will be low if objects with high reflectivity are in the same range of vision during measurement. One suitable method is to merge multiple captures at different integration times. It reduces the frame rate but increases the dynamic range. In May 2006 we have presented an alternative integration time controller based on mean intensity measurements. This solution was empirically found and showed a suitable dynamic range for our experiments without affecting the frame rate. It also alleviates the effects of small bothering areas. The averaged amplitude in dependency of intensity can be seen in figure 8. n IK I UX MJ1KI Z- iiOl 3MÚŨ 4MH Mnn llilnuil IRrguInf T luri Figure 8. Relation between mean amplitude and mean intensity. Note that the characteristic is now a mixture of the characteristic of each single pixel cf. figure 6 We used a proportional closed-loop controller to adjust the integration time from one frame to the next as shown in the following itemization. The control deviation variable Ia was assigned with a value of 15000 for the illustrations in this chapter. It has been chosen conservatively with respect to the characteristic shown in figure 8. 1. Calculate the mean intensity It from the intensity dataset It at time t. 2. Determine control deviation Dt It - Ia. 3. Update control variable ct 1 -Vp Dt ct for grabbing the next frame where ct and ct 1 are the integration times for two frames following one another Vp the proportional closed loop deviation parameter and Co a suitable initial value. Independent of the chosen control method the integration time has always to be adjusted with respect to the application. A .
