Public Lab Research note


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Phantom 3 Professional

by marfisistemidroni |

I removed the IR filter in my camera Phantom 3 professional that is already equipped with a NIR Sentera, I added the filter (red) infragram front of the lens, so you can also change other filter types. The problem that is reflected on the white balance. The drone can be managed with specific applications for the flight and the photograph although, to make findings of extensive vegetation it is necessary to perform an automatic route "nadir" in which shots are executed in sequence georeferenced which then can be processed using such software Agisoft PhotoScan or Pix4D mapper, to create a unique geo-referenced photos (orthophotos). These applications (at least the ones I know until now) do not allow the white balance, it is the only pix4D Capture but has only three options: auto, sunny and cloudy. For now I have tried to balance the white with the native application of the Phantom 3 (DJGO) which still has a number of more complete balance options (auto, sunny, cloudy, incandescent light, fluorescent light) at least to get an idea, I would like know if the photo that forwarding is close to the correct balance. In addition, in the event that generate an orthophoto, I should process it later with the plugin FIJI (could be 500 mb of photos) or individual photo shoots before processing, without losing the EXIF information about photos (Otherwise the photogrammetry software fail to develop). I apologize for any errors, but I'm using a translator. Thanks in advance to those who will be able to help me, greetings



5 Comments

Hi Mario,
White balance could be a problem. All of those preset white balance settings and the results from auto white balance will be very different from the results if a custom white balance is done as described here.

If the camera can save camera raw files, they can be white balanced after they are taken. If only jpegs can be saved, then it is difficult to get good NDVI results without custom white balance.

Here is the histogram of foliage in your photo:

0010Hist.JPG
Note that there is not much difference between the values in the red and blue (NIR) channels.

Here is the histogram for foliage in a photo which can be directly converted to NDVI (from this note):

0554Hist.JPG
Note that the blue (NIR) values are about eight times larger than the red values.

To convert your photo into a photo that can be converted to NDVI, you could try to adjust the color balance so foliage was a blue like in the photo above. I have never had much success doing this. The NDVI image is never as meaningful as when a proper custom white balance is set before the photos are taken. You might be able to find a clever way to do it.

Chris


Can you tell me whats the red filter used for....just taking off the infrared filter and getting R G B IR channels and separating those channels later would work the same right? .The channel separation can be easily done in Fiji App. I am also wondering in your case in RGB spectrum, the Red would be Near Infrared, Green would be Red and Blue would be Green right after adding red filter.Correct me if i am wrong. Can't a normal RGB camera take 4 spectrum after removing IR filter?

Look forward to your response.


With certain red filters replacing the NIR cut filter, instead of red, green, and blue channels, you get red+NIR, NIR, and NIR channels. Without adding the red filter, you get red+NIR, green+NIR, and blue+NIR.

Chris


Hi sorry about my english I from Uruguay and just bought a phantom 3 pro with NIR camera conversion. I've the same confusion about the channels of my NIR camera is capturing. The people who sold me told me that the modification was remove NIR filter and configured the software to not broke the hardware, that correct?. I want this to generate NDVI in diferents crop and then analize them. DJI_0017.JPG

That is a image captured by my drone. I did a color histogram in fiji and the results were:

resultados.jpg

The sellers tell me that there are lot of lut filter who do NDVI with the images captured like this, but I was reading a lot of tutorials on forums and couldnt know who lut is better for diferents things. ND in red channels seems too near to 255, and that thinks its wrong. I was worked with GIS programs to separte bands, but i don`t know wich band is NIR, Red, Green or blue. Thanks for help


I can't tell from the photo what kind of filter your camera has. My guess would be that it is a blue filter, so the red channel would be mostly NIR and the blue channel would be mostly blue. But I can't be sure. Do you have a link to the camera or lens you have? Do you know what white balance settings were used in your photo? If you can't do a custom white balance, taking photos which can be directly converted to NDVI will be difficult. Regardless of filter, both the red and blue channel will have to be exposed well (not over-exposed like the photo here) to get good results.

Chris


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