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Messages - nprokofyev

Pages: 1 [2]
General / Re: Validating invalid tie points
« on: July 03, 2020, 01:30:02 PM »
Have you tried to align one separated channel?

I saw something like that when I was trying to align data from two cameras in one chunk and these cameras weren't synchronized very precisely.

General / Re: RedEdge dark orthomosaics
« on: July 03, 2020, 01:16:10 PM »
As I can see from your formulae, you are calculating reflectances, which range by definition is in 0..1.
And very "bright" material like paper has reflectance about 0.9. Gray micasense CRP panel's reflectance is about 0.5 and as you can see it is still appears quite bright for an eye.
In the picture, you are looking at red channel reflectance of a grass field, which absorbs red light extremely well due to chlorophyl content. 0.1 in red is totally ok for grass.

Secondly, you are working within linear range (without gamma correction). Normally, RGB images are applied gamma 2.2 while being saved to JPG. Without gamma correction the image looks darker for human eye.

Thus the answer is: it is fine. The image would have been "brighter" if you had applied gamma and/or adjusted resulting image levels.


General / Re: Color correction and NDVI
« on: June 25, 2014, 10:08:43 AM »
Well, Aerie, NDVI calculation using brightness indeed is susceptible to false readings. And the open problem that is in front of me is to develop measurement method that operates reflectivities (as it is defined for NDVI in wikipedia) instead of brightness.
Reflectivity is a property of material and is independent to sun brightness, shadows, etc.

Anyway, you cannot calculate true NDVI simply comparing brightness of photos made in RED and NIR range.

General / Re: Color correction and NDVI
« on: June 19, 2014, 12:32:29 PM »
Aerie, could you explain in a few words how to calculate reflectivity? For example, if you have NIR photo, the measured parameter is pixel brightness. How to calculate reflectivity then?

General / Re: Color correction and NDVI
« on: May 29, 2014, 06:26:44 PM »
This is the IR LED in dark room. Photo with 760 nm filter.
sorry, had to cut, if you need a full-size raw, ask me in PM.

General / Re: Color correction and NDVI
« on: May 29, 2014, 04:39:48 PM »
  Do you have any examples or research you can pass along to help explain your findings?
Well, I am developing custom photosetup for NDVI, and have some sample photos in NIR with 720, 760 and 950-nm cutoff filters.
I can make a RAW photo of cigarette lighter in dark room, and you will see, all RAW channels will contain data.

General / Re: Color correction and NDVI
« on: May 23, 2014, 03:24:27 PM »
did you know that most of CMOS sensors are sensitive to NIR on either R, G1, G2 and B channels? If you have photos made thru the IR filter, just desaturate them. >95% of resulting "luminosity" is pure NIR.
As for RED, I think it is also not a problem to desaturate photos except one case. It is when smb using CMOS R channel instead of photos with red filter.

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