How to increase gain for old cores? - Page 1
Forum section: electronics / general

author: Logan
author_rank: Frequent Contributor
timestamp: September 18, 2021, 04:32:37 pm
content: Hi guys.I found most of the old thermal imaging cores have a very low contrast when viewing low delta T scenes. Even the Seek have a higher contrast than most of them(although with more noise), is it possible to change the auto-gain limit higher?Thank you.

author: Fraser
author_rank: Super Contributor
timestamp: September 18, 2021, 04:46:56 pm
content: You first need to detail the specific cores you have as then we will know what options are available to youFraser

author: Ultrapurple
author_rank: Super Contributor
timestamp: September 18, 2021, 04:53:30 pm
content: Short answer, probably no.The limiting factor with uncooled microbolometer thermal imaging cores is noise, not gain. In a low delta-t scene the wanted signal (image) may be of the same magnitude - or even lower - than the sensor's noise. So if you were to increase the gain you'd just get the same signal-and-noise mix, just bigger.You can 'force' gain in two ways: bigger (better) optics and / or temporal averaging. There's a practical limit to the aperture you can get in any optical system; I don't recall seeing any LWIR lenses of much more than f/0.7 (and those are rare). Temporal (frame) averaging will reduce the apparent noise, but at the expense of effective frame rate. All other things being equal, a rolling average of (say) 16 framesfrom the sensorwill reduce the noise by a significant amount - but if anything moves in the images, you'll see sixteen ghosts of it as the movement works its way through the averaging buffer. (Many cameras already include frame-to-frame averaging to varying degrees as part of the standard noise reduction algorithms so you may find there's no benefit to additional averaging.

author: Fraser
author_rank: Super Contributor
timestamp: September 18, 2021, 06:26:51 pm
content: Greater detail can often be extracted from an image using a decrease in the temperature span to which the Palette LUT is applied. Visible Noise levels in the image increase as the span approaches single figures and this is normal. Careful selection of temperature span, Centre temperature and palette can provide optimum visible contrast in a low Delta T scene. In order to achieve such, the camera or core needs to be capable of manual span and centre temperature setting and some high contrast colour Palettes can highlight temperature transitions. High Contrast Rainbow is such a palette.Finally, if a core offers high and low sensitivity modes of operation, the high sensitivity mode should be selected. This range usually covers approx -20C up to +120C. The low sensitivity mode provides greater temperature measurement capability but with higher noise levels present in the image and, in some cases, lower contrast in low Delta T scenes due to increased temperature span.Fraser

author: Bill W
author_rank: Super Contributor
timestamp: September 18, 2021, 07:19:45 pm
content: To add to things here, some of the early cores (Raytheon 2000AS and related) were quite limited in the available image processing to the point of being a fixed temperature - brightness map. As said this was not so big an issue if noise limited anyway.You might though have:A sensor losing vacuum (early ULIS & Indigo)A stuck iris (Raytheon BST)Lost setup parameters (known with Raytheon BST)The software and hardware routes to adjust a Raytheon BST gain and offset are in the forum.Bill

author: Logan
author_rank: Frequent Contributor
timestamp: September 19, 2021, 01:16:59 pm
content: Quote from: Fraser on September 18, 2021, 04:46:56 pmThis is a general question, because I found most of thermal cameras - especially old ones - have this problem.

author: Logan
author_rank: Frequent Contributor
timestamp: September 19, 2021, 01:19:13 pm
content: Quote from: Ultrapurple on September 18, 2021, 04:53:30 pmThe problem is many thermal cameras produce a too flat image before the noise is unbearable. Even if the SNR are same, I'd rather have a higher contrast picture.

author: Logan
author_rank: Frequent Contributor
timestamp: September 19, 2021, 01:21:11 pm
content: Quote from: Bill W on September 18, 2021, 07:19:45 pmThis is ridiculous

author: Fraser
author_rank: Super Contributor
timestamp: September 19, 2021, 04:34:57 pm
content: What you are actually asking for is not higher gain at the sensor array, but greater contrast at low Delta T and this is normally provided in the image processing stages of the camera design. This increased contrast for low Delta T scenes is achieved through the use of histogram equalisation that provides a prettier picture but effectively destroys the Radiometric data coming from the sensor array. In order to preserve the Radiometric data the camera system can use two image streams, one Radiometric and the other RGB histogram enhanced. This comes down to pretty pictures vs Radiometric images.Fraser

author: Bill W
author_rank: Super Contributor
timestamp: September 20, 2021, 10:25:10 am
content: Quote from: Logan on September 19, 2021, 01:21:11 pmMaybe, but true. if you want more contrast from them, then you simply adjust the display contrast. At that era it usually meant on G1 of the CRT.Bill

author: downtodo
author_rank: Contributor
timestamp: September 20, 2021, 11:48:29 am
content: Put a high-temperature object into the scene to make the temperature difference in the screen larger, and you can see it more clearly.

author: Fraser
author_rank: Super Contributor
timestamp: September 20, 2021, 12:04:50 pm
content: Downtodo:“Put a high-temperature object into the scene to make the temperature difference in the screen larger, and you can see it more clearly.”Sadly this is not really a solution to the OP’s problem……Placing a high temperature object in a scene that is otherwise low temperature can actually make matters worseThe camera will respond by increasing the temperature span and so further reduce the contrast in low Delta T areas of the scene. In the case of noisy imaging cores, such as the Seek Thermal classic dongles, the improvement in image quality does occur as the increased span effectively hides the noise. That said, the low Delta T areas contrast is not increased but the reduced image noise may make them more visible.

author: Logan
author_rank: Frequent Contributor
timestamp: September 21, 2021, 02:29:35 pm
content: I was thinking maybe there's some simple hardware modding to increase gain, such as changing a resistor... I'm too stupid.

author: Bill W
author_rank: Super Contributor
timestamp: September 22, 2021, 10:20:00 am
content: Quote from: Logan on September 21, 2021, 02:29:35 pmDoing that at the sensor (any type) would throw out all the calibrations etc so would involve a lot more work to get the camera working again, and certain back end processing might well compensate for higher input and you'd end up where you started.However for the Raytheon BST they have a route for analogue control of the image processing gain / offset, but the same as adjusting monitor contrast / brightness.Bill