I have been received a lot of questions asking what is EV and TH and how to adjust them to the best situation. This blog will provide you a clear definition of EV and TH, and show you how the settings will affect the scan by the Phiz 3d scanner.
EV stands for Exposure Value:
If you are familiar with photography, you may know that EV is a number represents a combination of a camera’s shutter speed and aperture size. Higher EV will generate a brighter photo, reversely, lower EV will generate a darker photo.
Why this is important to us? Because it will affect a lot on how the phone camera capture the laser line. Let me show you some example below.
When EV button to the very left (high EV), the camera will capture a very bright laser line meanwhile when EV button to the very right (low EV), the camera will capture the laser line barely. The preview button will generate a binary image from your original capture based on the threshold (we will talk about this later), and as we can see, high EV picture will be converted to a binary image with very thick line and low EV picture will be converted to a binary image with almost nothing in it. If you go with this two extreme setting, it will not give you a good scan result.
If we pick somewhere in middle, then we will get a clear and complete line to calculate the point cloud.
Now let’s talk about the TH.
TH stands for the binary Threshold Value:
When we want to let the brighter part stand out, we normally convert original image to grayscale image and then convert the grayscale image to binary image with threshold value. Every pixel in grayscale image will have a number to indicate how gray it is, from 0-255. 0 means black and 255 means white. And the number in between indicates different gray. We can make grayscale image to binary image by applying threshold value. For example, threshold value is 80, then all pixels which number lower than 80 will be black, meanwhile all pixels which number higher than 80 will be white. It will be no more gray color in binary image.
Again, why this is important to us? Because we capture the green color on the image but what if there is a lot of refection. Just like below.
The refection area will be counted as a part of laser line and it will generate a lot of noise. Even though we have noise cancelling algorithm but it will not delete them all. So we need a better threshold to get rid of unnecessary part from the beginning.
If we pick correct threshold, then the line will be clear and no more reflection will be captured.
In conclusion, EV and TH need to be adjust at the same time. To check if the setting is correct, the easiest way is hitting “preview” button and see if the line is clear and complete. If preview is good, then EV and TH should be good to go. I wish this blog is useful for you and if you have any further questions, please do not hesitate to contact me. Cheers.
By the way, the david head in the above images was 3D scanned by Phiz 3D scanner and 3D printed out by us.