Thermal camera testing suggestions please - Page 1
Forum section: electronics / general

author: Ultrapurple
author_rank: Super Contributor
timestamp: October 26, 2017, 07:20:59 am
content: Hi folksAs I have written elsewhere, I'm going to make time soon to test, side by side,a Therm-App 384x288 8.7Hz (17µ)a Therm-App 384x288 25Hz (17µ) (after-market upgrade)a Therm-App Pro 640x480 25Hz (17µ)A limited set of lenses are available2 x 19mm f/1.11 x 35mm f/1.11 x 6.8mm f/1.41 x 12.8mm f/1.0I believe the field of view of the 35mm lens on the 640x480 imager is similar to that of the 19mm lens on the 384x288 version but I have yet to confirm this. The 6.8mm lens vignettes very badly on the 640x480 sensor; the 12.8mm lens does so slightly. This is why I suggest 2x19mm and 1x35mm as the best option.I plan to use the same driver software (ThermViewer) for each camera, set with the same options. (As an aside, I will use its background removal technique to remove fixed sensor imperfections; this is essentially the same as a shutter calibration on other cameras and removes static sensor imperfections that aren't dealt with by the various calibration maps that come with the sensors).I don't have access to any professional thermal test gear such as flat plate targets; a bowl of ice water is the limit of my temperature calibration possibilities, alongside an adjustable temperature soldering iron.So, my question: assuming I have all three cameras at the same (room) temperature, physically side by side, and pointing at the same (low thermal contrast) indoor scene, am I likely to get results that will let me subjectively judge the performance of the three cameras? I'm thinking in terms of noise and sensitivity; naturally, the Therm-App Pro will be significantly higher resolution.Have I missed anything? Are there any other obvious tests I should do (eg running 10 seconds of video and using RegiStax to see what the underlying image quality might be)?It will be several days before I am in a position to run these tests so I will appreciate any suggestions.

author: LesioQ
author_rank: Regular Contributor
timestamp: October 26, 2017, 08:24:07 am
content: Use Your pet - dog or cat in sleep mode as a stabilised source of heat image profile.Fur details clarity is a good test

author: Ultrapurple
author_rank: Super Contributor
timestamp: October 26, 2017, 08:58:51 am
content: Good idea - except that my only 'pet' is a stuffed toy aardvark called Boris; his thermoregulation is decidedly poor. I did make some images of a Barbary macaque on Gibraltar recently and the fur details were definitely a good test of resolution, sensitivity and focus - but they're protected wild animals (and >1500 miles away), which raises some practical difficulties...

author: Mjolinor
author_rank: Frequent Contributor
timestamp: October 26, 2017, 11:53:43 am
content: A wife can be handy for this. They make so much hot air and often blow so cold that extremes of the temperature range can be defined from a few sample shots.

author: Bill W
author_rank: Super Contributor
timestamp: October 26, 2017, 12:31:12 pm
content: A kettle boiling water may also be useful.Video of the steam etc for 'moving things'Stills of the hot cable for gradationThe large hot object might embarrass the image processing more than a small hot object, so exposing either gradation / quanisation or noise in the lower contrast areas.Car engine bay, with garden beyond.Again using a large hot object to test either gradation / quanisation or noise in the lower contrast areas.regardsBill

author: IwuzBornanerd
author_rank: Frequent Contributor
timestamp: October 27, 2017, 01:11:58 am
content: I think it would be good to show what the noise looks like with the default app with the old camera for comparison purposes. Could you also use the standard app to get temperature readings as calibration values?If the soldering iron turns out to be hotter than the rated sensing temperature of the camera you might use an overheated carbon comp resistor as a hot item, at least if you have something to measure its temperature with.It would also be interesting to see what you get when you fill a frame with the surface of that bowl of ice water and a narrow temperature span. What I found with the new Seek is that after calibrating against a uniform ambient temperature surface there was a pattern with slight temperature differences when aimed at a surface near 0*C, and moving the surface did not change the pattern, so I figured it was related to the thermal distribution on the camera board or sensor module. I have not dug into that, though...I'm curious to see the effect of the F/1.4 lens vs. the F/1.1 lens on the same camera. I expect it to cause the temperature readings to be significantly lower unless the software has an aperture selection option that corrects for the change from F/1.1. I also expect it will show more noise compared with a wider aperture at the same temperatures. I hope to test that out with my Seeks soon.

author: Ultrapurple
author_rank: Super Contributor
timestamp: October 27, 2017, 08:18:44 am
content: The problem with the default Therm-App app is that it is critically dependent on the camera calibration files, which are not uniformly good. For example, the default files for my Therm-App Pro have several large lens reflections that are extremely noticeable in low-contrast images. ThermViewer (and ThermApp Plus for the 384x288 cameras) correct these background deficiencies via a manual 'analyze noise' system that is essentially the same as a shuttered TEC.The first image shows the rather poor default 'black level' calibration on my Therm-App Pro (albeit with a 13mm lens that vignettes slightly so you can ignore the dark corners). ThermViewer levels this out (±noise) to a flat field, as seen in the last image. (As an aside, someone - Fraser? - mentioned some time ago that there are various bias voltages on a thermal sensor that affect sensitivity, and speculated that the Therm-App Pro may have been tweaked for maximum sensitivity at the expense of max/min range. It remains to be determined whether this is the case, but the Pro definitely does wander around a bit: the background pattern below will normally start showing up within about a minute of suppressing it, though nowhere near as strongly, A quick re-analyze sorts it out).The second image is the uncorrected background of my Therm-App updated to 25Hz. The background is my fault - Jinhua provided me with an utility to generate new calibration data but I didn't manage to do it quite right. I may have another go someday. The third and fourth images show the regular 384x288 Therm-App on ThermApp Plus with no correction and with full correction and basic real time enhancement. These can be further improved by stacking (eg Autostakkert! or RegiStax) and/or superresolution.The regular Therm-App and Therm-App Pro do not claim to be ratiometric and, in my experience, only give ball-park temperature measurements. We have previously done work comparing the sensitivity of different lenses (eghere,here,hereandhere, among other places) and the difference in sensitivity between the f/1.4 and f/1.0 lenses is clear. I f time permits I will do some further experiments with the four different focal lengths (6.8mm f/1,4, 12.8mm f/1.0, 19mm f/1.2 and 35mm f/1.1).The ice water idea is a good one and I will definitely try that. I'll also have a go at other temperature 'measurements' but my kettle is shiny (=emissivity issues) andthe soldering iron, whilst temperature controlled and adjustable from ambient to >400°C, probably wavers up and down by several degrees at low-to-medium ranges. We'll see.

author: Vipitis
author_rank: Frequent Contributor
timestamp: October 27, 2017, 10:15:38 am
content: I don't know if it applies to you, but I got an 3D printer for example, where I can set the Nozzle and heated bed to a specific temperature. That could be a nice test platform for me.

author: Ultrapurple
author_rank: Super Contributor
timestamp: October 27, 2017, 10:49:52 am
content: Good thought.Some time ago I developed a PCB that included a large spiral track on one side as an inductor. It has enough DC resistance to make a useful heating element (at least for small temperature rises). If I spray it matte black it's possible it will make a decent thermal target. I've used it before, without painting, as a thermal target but had problems with its reflectivity and emissivity.I can attach a thermocouple probe to it and read the actual temperature, which will provide a reference point for temperature measurements made with the cameras.

author: Vipitis
author_rank: Frequent Contributor
timestamp: October 27, 2017, 11:54:29 am
content: What some people might look for is actual application examples. So electronics, not just PCBs also power poles or large machines. Plumbing, like Pipes, also pipes behind a wall with warm water for leak detection. Home inspection. Some roof and windows in the night just to see reference. Medical, on human and animals, I have seen people using their flir one for horses. Defense. Detection at range, will be a good test for those lenses, detection and identification. Art - this is your department.

author: Bud
author_rank: Super Contributor
timestamp: October 27, 2017, 02:15:36 pm
content: Quote from: Ultrapurple on October 26, 2017, 07:20:59 amA coffee mug warmer

author: Bud
author_rank: Super Contributor
timestamp: October 27, 2017, 02:23:41 pm
content: Also, simply a powered computer LCD monitor showing a blank screen. Large surface and smooth temperature gradient. Guess matt screens will work better for the purpose.

author: Ultrapurple
author_rank: Super Contributor
timestamp: October 27, 2017, 02:33:52 pm
content: The coffee warmer is a good idea - I've only ever come across them as simple USB-powered devices, never one with a digital display and (presumably) enough oomph to make it worthwhile.A search on eBay found preciselyoneof the coffee warmers described above - for $40 plus $19 shipping USA-UK plus $14 import taxes.My monitors and TVs tend to be quite 'streaky' from a thermal viewpoint, but there are probably large enough bits at more or less constant temperature to be worthwhile.

author: Bud
author_rank: Super Contributor
timestamp: October 27, 2017, 03:36:06 pm
content: I grabbed that picture from Amazon - that model seem to be sold at a lower price on Amazon, try there.If you do not need a adjustable temperature source, there are cheaper coffee mug warmers models available, mains powered. I have one that is very old , holds temperature pretty good when warms up. I'd think if to put a painted copper plate on it to add some thermal mass, that may minimize drift in temperature over time.

author: Chanc3
author_rank: Frequent Contributor
timestamp: October 28, 2017, 07:37:16 am
content: Ultrapurple, where in the UK are you? You're more than welcome to carry your tests out on our Fluke 4181 and 4180 blackbody calibration sources.

author: Ultrapurple
author_rank: Super Contributor
timestamp: October 28, 2017, 08:34:23 am
content: Quote from: Chanc3 on October 28, 2017, 07:37:16 amThank you - that's very kind. I'm in Bedfordshire, and make occasional, planned trips down to the West Country and Kent.

author: Chanc3
author_rank: Frequent Contributor
timestamp: October 28, 2017, 08:43:40 am
content: Ok, well we're just outside Portsmouth, so if you're in the area at any point, drop me PM!