# K coefficient for Reflectance Estimation

#1

When we calculate K coefficient, we use calibration panel of parrot sequoia. The camera gives us a 3 different image of calibration panel that are same but taken different mode. So my question is:
I take calibration panel image for all bands and calculate average values of panel like this,

so I can’t use the Red_000 due to saturation. If I use Red_001 I obtain K values as 0,59. if I use 3. image I obtain K value as a 0,96. As a result of this my reflectance values are changes. Which one is true for me?

#2

Could be related with the gain factor?

#3

Hi!

I am trying to compute the K factor and I stack over the same problem: How I deal or mean those three numbers?

#4

This question answered by pix4d support team,

When you launch the radiometric calibration with Sequoia the camera takes 3 sets of images with different exposure in order to avoid over or underexposure. Only one set of images can be included in a project. A set of images consist of one image per each band (green, red, rededge, nir). You will have to choose the best set of images (the one not over or under exposed). When the digital number of the target images are higher than 63000 we consider them overexposed.

#5

What if all images are saturated? I have a set of images an all values are 65472. I read that is usefull to use a reflective item near the calibration panel to avoid overexposion.

Can you share the link for the question answered by pix4d? I could not find it in the forum.

And for last, if I use for example the second image of the set for a band (0001) , I have to use the image with that same exposure for the other bands?

Thanks!

#6

As I know my knowledge, all images have their own exposure value. You can find exposure value from exif information of image that you choose for calibration

#7

Thanks for the tip! It is very useful!