histogram

OpenMV Boards
1

How do I read the IDE histogram. I want to find the pixel intensity along an X line segment.
I use:
script “helloworld_1.py” ,sensor.set_pixformat(sensor.GRAYSCALE) , sensor.set_framesize(sensor.VGA)

IDE Histogram “grayscale color space”
res(W:640,H:480)
Questions;

  1. Why does the X scale only go to 254 instead of 640?
  2. What do the pyramids on the Y scale indicate?
  3. Why is there no value for the pyramid height?
  4. What are the units on the eight items below the histogram, i.e. min, max, etc.

Regards,
Jim Sullivan

2

A histogram is the chart of the number of occurrences of a pixel value.

Grayscale 0-255 per pixel. The histogram then shows the distribution normalized such that all bins when summed up sum to 1. There are 256 bins in the histogram. If you stop the camera, and then hover your mouse over an area on the histogram it will show the bin value. The units below the histogram show important color value metrics for the scene. Min=Min Grayscale Pixel in the Image, etc. UQ/LQ are the 25% percentile and 75% percentile. Median is the 50% percentile. Please refer back to your stats classes on what these are.

3

Thanks,
I was in college for 6 years and got two Engineering Masters degrees and I never new what a histogram was until now. I always thought it was a simple bar chart.
Thanks for completing my education,
Jim

4

Yes, most of the time you only see less than 10 bins since it would be hard do more by hand. But, on a computer, you can have a bin per value. :slight_smile: