On my multicopter, I have a Boscam HD19 camera. This camera was explicitely developed for use on UAVs and has some interesting functions, like live video out, full HD recording and taking photos. The recording functions can also be controlled via the UAV's remote control, which makes it especially useful. The stock lens is very wide-angeled and - in my opinion - not of excessively good quality. Fortunately, the HD19 uses a standard 12x0,5mm thread for lenses and good but cheap lenses in various angles are available from the internet.

As of all digital cameras, the sensor of the HD 19 is also sensitive to infrared light. However, the HD19's stock lens has an IR-cut filter because IR light is very prominent in the light spectrum and would otherwise cause the picture's colors to be distorted.

So, to get infrared light, we either have to remove the IR-cut filter from the stock lens or get a lens without filter. As I didn't like the wide angle of the stock lens and I had some problems with unsharp edges, I decided to buy a 6mm lens on eBay for about 6€ incl. shipping. It is noticeable that the HD19 has a 1/2.5" sensor. Most cheap CCD and CMOS cameraswith M12 lenses have 1/3" or 1/4" lenses which leads to a small tunnel effect on photos with the HD19. Thus, only lenses for 1/2.5" sensors should be used. Those lenses are also often called "HD" or "3 Megapixel / 3MP lenses".

thumb IR beforeAfter replacing the lens, the images look like the one to the right (click picture to enlarge). Colors don't seem to match, especially colors of plants, and the whole picture is tinted red/pink. That is pretty much how it is supposed to look like. The automatic white balance function of digital cameras is calibrated for the visible light spectrum only. IR light throws it off very much and generally, the IR part is very strong on the general spectrum. IR light has a longer wavelength and thus penetrates e.g. fog or clouds much better. This photo was taken at 9 in the evening on a cloudy day, but it's still very bright. As for the plants, the foliage of a living plant reflects IR light very well. That's why plants appear very bright in an IR picture. IR reflectivity is also a good indicator of a plant's health.

thumb IR autowhitebalBut of course, we don't want all pink pictures, hence we have to do a bit of postprocessing. I use GIMP for postprocessing of photos. The necessary functions are also available in other programs, like Adobe Photoshop. The easiest way to get reasonably good pictures is to use the automatic white balance function of GIMP (menu Colors -> Auto -> White Balance). This already gives a nice result but it's still very pinkish (see left, click to enlarge). To get better results, we still have to do some corrections and those are best done with color curves (menu Colors -> Curves). Select the Red channel and try to lower the level around 100-120 a bit.

thumb IR afterAfter correcting the Red channel and a tiny little bit also Green and Blue channels, the result is pretty ok (see right, click to enlarge). During the postprocessing, we lose a bit of dynamic range (compare e.g. the door of the black car left of the image's center), but the normal colors are almost totally correct now. Vegetation still is a bit pinkish but that is not easy to correct without losing a big amount of dynamic range and contrast in the process.

To make things easier, I have written a small Scheme script for GIMP which does the correction automatically. You can find it from my download area.

Part 2 will cover postprocessing of images which were taken with an IR-passthrough filter.

Original article URL: http://stefan.gofferje.net/news-blogs/uav/170-ir-photos-with-the-bo...

Views: 4203

Comment by healthyfatboy on August 11, 2013 at 7:11am

It won't let me download the script for whatever reason.

Comment by Stefan Gofferje on August 11, 2013 at 7:15am

Download fixed.

Comment by Cala on August 11, 2013 at 7:56am

Great work :). How do you take photos? It' has timelapse? or motion detection? You have to use an external battery? Thank's

Comment by Stefan Gofferje on August 11, 2013 at 8:18am

It has 2 serial image functions. Automatic trigger every 3-30s (configurable) and taking of multiple pictures at trigger. The automatic function can be activated through a button on the camera or you can also control it via an R/C channel. I don't know the exact thresholds, but +100% activates video recording, 0% is standby and -100% takes a photo - or multiple, if the serial image function is active.

You have to use external power because it was designed as an UAV/FPV camera. It comes with a cable that connects directly to Boscam or other video transmitters and gets power from there.

Comment by Cala on August 12, 2013 at 12:12am

Thank Stefan, I have in proyect to modificate a HK wing camera but this one sounds better, easyer and no so expensive :)

Comment by Hein du Plessis on August 13, 2013 at 11:27am
Thank you! Could you perhaps link to that ir filterless lens on ebay?
Comment by Stefan Gofferje on August 14, 2013 at 8:55am

Search eBay for CCTV Megapixel lens or CCTV 3MP lens. usually, if it's not mentioned, they don't have an IR-cut filter. Also the text "IR" on the lens frame means no filter.

Comment by Hein du Plessis on August 14, 2013 at 12:57pm

Thank you - IR aside - would it merit replacing the stock lens with a "better" lens as you say? Would one see an improvement in quality in visual spectrum?

Comment by Stefan Gofferje on August 14, 2013 at 1:07pm

You mean in regards to the frequent complaints about too pale colors? No. Using a better (bigger - more light) lens could, however, improve the image quality on overcast days.

Comment by Hein du Plessis on August 14, 2013 at 1:10pm

Ok, thanks. My gripe is the apparent noise in the image, compared to the gopro, but it's a fraction of the price, so fair enough..


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