Radiometric vs Non-Radiometric Leptons

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GL-ITC
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Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Thu Jun 18, 2020 9:21 am

Hi,

Its probably not the right place to be asking the question but I'm struggling to find a specific answer, how does a radiometric lepton (3.5) differ from a non-radiometric. More specifically when reading about radiometric measurement it says each pixel can be interpreted as a temperature value. What is a pixel from a non-radiometric lepton considered then, surely it could also be mapped back to a temperature as well? In which case how are they different.

I have been trying to understand where the object detection examples you provide actually make use of the radiometric aspect of the Lepton. My understanding is that a radiometric camera will give each pixel a temperature value and this data is stored in the image metadata. So why are the object detection examples converting a color to a temperature using the map_g_to_temp() function and not using the raw temperature values that a radiometric camera is supposed to provide.

My other question is how do I maintain the image as a radiometric image when sending it between devices because it currently seems like I am sending a standard .jpg file instead of a radiometric .jpg file which would have the temperature data in the images metadata. My current compressed .jpg images don't seem to contain this information which is critical if your doing post processing.

Thanks,
Gar
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Thu Jun 18, 2020 3:25 pm

The Lepton outputs 14-bit data. We are an 8-bit device. So, given the min and max temp we scale that 14-bit data to 8-bits.

If you want to edit the c code on the device to process 14-bit data you can.

Radiometric means that the Lepton will try to output valid calibrated temperature readings. Without this feature the thermal image just looks pretty but isn't accurate in any way shape or form. For like a hot spot detector this is fine. The thermal image doesn't need to be calibrated.

The Lepton has a "hot spot" API call you can do to get the temperature of what's in the center of the image. We don't implement this feature in our firmware currently... But, it would allow you to get a 14-bit temperature reading given a region of interest. This hotspot reading is valid for any Lepton.
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Thu Jun 18, 2020 3:39 pm

Hi,

By converting from 14 bit to 8 bit is the radiometric aspect lost?

So really in the current implementation of the Lepton code you provide, it doesn't make use of the radiometric aspect of the camera? I'm not sure I fully understand your explanation. Does that mean then the map_g_to_temp() function is not providing me with a valid calibrated temperature reading in which case what does that temperature actually represent?

This page https://flir.custhelp.com/app/answers/d ... /related/1 references radiometric data which I'm trying to understand if I can access on the H7/ ideally pass the radiometric jpeg to another device for post processing. It seems like the example code you have for the lepton is treating it as a "normal" jpeg which is different.

This line from your docs would suggest it should be giving an array of temperature values:
sensor.IOCTL_LEPTON_SET_MEASUREMENT_MODE - Pass this followed by True or False to turn off automatic gain control on the FLIR Lepton and force it to output an image where each pixel value represents an exact temperature value in celsius.
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Thu Jun 18, 2020 6:52 pm

You are confusing yourself by thinking this is more complex than it is. All we are doing is scaling the output to 8-bits. The 8-bit value just looses precision - not accuracy. Meaning that instead of knowing the temperature to two decimal places you only know it to one.

Non-radiometic units might have precision but not accuracy. I.e. it will tell you temperature readings but they are wrong.

In non measurement mode the sensor runs an algorithm called AGC which adaptively scales the 14-bits to 8-bits using a method that changes per area of the image. This gives visually pleasing results but you will be unable to extract the temperature information from the image.
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Thu Jun 18, 2020 6:54 pm

With jpeg compression on a thermal image you will effectively further comprise the precision depending on the jpeg quality. That may or may not be okay for you. Jpeg compression will probably result in 1/2-bits of precision loss effectively.
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Thu Jun 18, 2020 6:54 pm

You can save images as BMP files to avoid this
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Tue Jul 07, 2020 11:10 am

Hi,

Could you provide me with a link to the file that scales the data from 14 bit to 8 bit please? I would like to look at the source code as it seems I will need to edit it to get the radiometric data that I require.
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Tue Jul 07, 2020 11:57 am

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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Mon Jul 13, 2020 6:43 am

Hi,

Is the logical AND of value and 0xff in the switch statement where the 14 bit to 8 bit conversion is actually happening. I had a quick look at the code and specifically looked up the 0xff operator which gives you the last 8 bits of the value. The code I'm looking at is here:

Code: Select all

IMAGE_PUT_GRAYSCALE_PIXEL(image, t_x, t_y, value & 0xFF);
If that is the case, would a quick approach to get the raw 14 bit data be to remove this AND operation as well as the temperature conversion code:

Code: Select all

float celsius = (value * 0.01f) - 273.15f;
celsius = IM_MAX(IM_MIN(celsius, max_temp), min_temp);
value = IM_MAX(IM_MIN(IM_DIV(((celsius - min_temp) * 255), (max_temp - min_temp)), 255), 0);
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Mon Jul 13, 2020 11:13 am

Hi, the camera has no way to display 14-bit data. None of our code works on that pixel depth.

If you want to shove a 14-bit grayscale output into a 16-bit RGB565 image you can do that. However, the only thing you can do then is just write the image to disk as a binary file. None of our CV methods can be used on it. But, you'd be able to save the raw 14-bit images.
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Mon Jul 13, 2020 11:25 am

Hi

I would like to access the raw temperature data the camera produces I understand that I would still need to convert it to 8 bit or whatever for display purposes. So in short I would like to have an array of raw temperature values and the 8 bit greyscale image. I understand what you mean about converting to 16 bit and its limitations.

Maybe the way you have it implemented is enough for what i need without having to change the firmware. We are trying to use the lepton to find hot spots on server racks and then direct the cool air towards that hot spot. We wanted to have the raw temperature data the camera produces as well as the image for any post processing we do.
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Mon Jul 13, 2020 1:02 pm

There's another thread about using the RAD spot-o-mter. This is what you want to use. It lets you get the temperature of an ROI.
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Mon Jul 13, 2020 1:18 pm

Yes I saw it. The spot meter requires me to give it the coordinates of an area I want to check. In terms of a server rack I cant say the hotspot will always be at a specifc point, hence why I wanted the raw data as well as an 8 bit greyscale image. We would then implement our own hotspot detection code to find the the hotspots and then use the raw temperature data to get temperatures for each of the hotspots which would be passed to a centralised cooling system.

The radiometric roi is not dynamic enough is what I'm trying to say
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Mon Jul 13, 2020 2:06 pm

Yes, but, you can move the ROI to a new location based on 8-bit hotspot tracking.

...

But, really, here's the deal. Why do you need 14-bits? 8-bits gives you enough resolution if you set the min and max temperature. You seem to be asking for a feature that you don't need.

What's your min and max temperature range? If you are going from 20C to 60C then 8-bits gives you ~0.15C precision.
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Mon Jul 13, 2020 2:58 pm

Yes maybe your right, I'm just trying to understand it which the source code definitely helped with. The critical temperature range is 20 to 40 degrees, you wouldn't really want a server reaching 40 degrees anyway.
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Tue Jul 14, 2020 6:54 am

Hi,

So I had the temperature settings set at -10 and 140 which by my calculations would result in a possible loss of precision of approximately 0.58C in an 8 bit greyscale image, is that correct? I didn't intend on leaving the temperature window that wide going forward anyway but I didn't realise it could potentially introduce that level of inaccuracy?

By moving the ROI based on 8 bit hotspot tracking, do you mean use greyscale colour tracking to find the hotspot then send the coordinates of the hotspot to the builtin Flir ROI functions using the IOCTL commands to get the raw temperature data (min, max and avg)?
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Tue Jul 14, 2020 12:09 pm

Yes, that's correct.

And for your second question yes too. You'd tell the camera which ROI you want dynamically and then query the precise temp from that.
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Wed Jul 15, 2020 8:34 am

Hi,

I would like to summarise my understanding of this code and see If you can tell me whether I am on the right lines or not:

Code: Select all

int value = __REV16(row_ptr[fast_floorf(x * scale_inv)]);

                        if (measurement_mode) {
                            // Need to convert 14/16-bits to 8-bits ourselves...
                            if (!radiometry) value = (value - 8192) + kelvin;
                            float celsius = (value * 0.01f) - 273.15f;
                            celsius = IM_MAX(IM_MIN(celsius, max_temp), min_temp);
                            value = IM_MAX(IM_MIN(IM_DIV(((celsius - min_temp) * 255), (max_temp - min_temp)), 255), 0);
                        }

                       .....

                        switch (sensor->pixformat) {
                            case PIXFORMAT_GRAYSCALE: {
                                IMAGE_PUT_GRAYSCALE_PIXEL(image, t_x, t_y, value & 0xFF);
                                break;
                            }
If radiometry is enabled then do value = (value - 8192) + kelvin otherwise convert to celsuis. This line seems to be taking the FFC into account.
Check if the celsius value is less than max_temp and greater than min temp.
Im not 100% sure what the IM_DIV function is checking but I can see you are converting the values to between 0 and 255 - if you could explain that in more detail I would appreciate. And then provide the image with the coordinates of the pixel and the 14 bit to 8 bit converted greyscale value.


Getting back to my previous issues with accessing the raw data. I am not trying to display 14 bit data I simply want an array of celsius values or better yet an array of values that have no conversion applied to them or no clamping. The reason I need this is the temperature clamping you do means I lose all temperature data outside of the temperature window which I cannot lose. Or at least thats how I have interpreted all of this.
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Wed Jul 15, 2020 1:07 pm

Hi, help support is for the features we have exposed. If you are going to ask questions about the code you should make an error to install a good editor and then lookup what all parts do. IM_DIV() for example is the divide operation with protection for divide by 0.

If you want to understand that code read the datasheets for the FLIR Lepton 1/2/3. I don't remember exactly why it's done like that in our code. But, it's correct.

...

Regarding the 14-bit data any. I has a todo list task to support the FLIR Lepton in the FIR module. When this is done you will be able to get the 14-bit image. However, don't expect this for a few months.
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Wed Jul 22, 2020 9:17 am

Hi,

I completely misread one of your earlier responses in this thread which is why I got so confused. You said
in non measurement mode the sensor runs an algorithm called AGC which adaptively scales the 14-bits to 8-bits using a method that changes per area of the image
. I have since looked at the flir data sheet in more detail and see that the 16 bit raw value was what i needed because I want tlinear output enabled:
With AGC disabled:
▪ With 14-bit raw data the first two bits of each pixel's two-byte word are set to 0.
▪ With TLinear output all 16 bits are used.
I had misread and thought I needed the 14 bit value but I don't as you correctly said. I have since modified the firmware so I am getting the 16 bit scaled output. Thanks.
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Wed Jul 22, 2020 11:18 am

Cool
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Fri Jul 31, 2020 6:40 am

Hi,

Possibly a foolish question but do you think there is any reason why the openmv board couldn't be used to calibrate the lepton 3.5 as per the Flir guide https://www.flir.com/globalassets/impor ... -guide.pdf. I know it mentions communicating with the camera over i2c and using a VoSPI stream to take frames (which is basically what you do anyway when you take a snapshot.) Given that the ioctl functions can call the sdk commands I'd image it would work, just wondering if you think there is any reason it won't.
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Fri Jul 31, 2020 10:55 am

Yes, you can do that with the OpenMV Cam. And if you are feeling very generous you can post the python code here that performs the calibration (it would be a huge benefit to others).
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Fri Jul 31, 2020 2:12 pm

Yeah no problem. I won't get to it immediately as I have a few other features to develop first but when I eventually get it done I'll post the code. Thanks
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Re: Radiometric vs Non-Radiometric Leptons

Postby Stub » Fri Aug 07, 2020 11:57 am

Hi,

I have designed and built a low cost black body - if you need one to help with this process please let me know.
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Re: Radiometric vs Non-Radiometric Leptons

Postby RECOVA » Sat Aug 08, 2020 10:44 pm

Hello,
I am trying to obtain the temperatures of each pixel of the lepton 2.5, could you tell me which would be the SDK for the configuration, I have tried with the example codes but I get sensor control failed. your help please
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Sun Aug 09, 2020 12:42 am

Hi, please read the forums posts by GL-ITC on this. He's already covered this topic is a lot of detail.

search.php?author_id=1812&sr=posts

Summary answer if you don't feel like reading all the threads from him:

-> The examples provide a valid temperature that's accurate and if you are trying to do something with richer data you aren't gaining much. You should follow them.
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Thu Oct 15, 2020 4:40 am

Hi kwagyeman

Just curious if theres any update on this
Regarding the 14-bit data any. I has a todo list task to support the FLIR Lepton in the FIR module. When this is done you will be able to get the 14-bit image. However, don't expect this for a few months.

Thanks
G
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Thu Oct 15, 2020 11:40 am

It’s coming up to do. I have to get this working for the pure thermal openmv cam.

Note that the image will just be returned as an array of floats with each float being the pixel temp.
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Sat Oct 17, 2020 5:45 am

Hi Stub,

You mentioned that you had developed a low cost blackbody.
I have designed and built a low cost black body - if you need one to help with this process please let me know.

I was wondering if you could elaborate on that? Have you used it to calibrate a Lepton 3.5 and if so what sort of measurement accuracy are you seeing? I tried to send you a PM but the message never leaves the outbox for some reason.

Kind regards
G
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Re: Radiometric vs Non-Radiometric Leptons

Postby Stub » Sat Oct 17, 2020 2:13 pm

Hi,

I have used it to provide an accurate threshold so that any pixel above the known temperature of the black body is definitely above the set temperature and any below are not. It was for a low cost skin temperature alarm.

I have not used it for the Flir calibration techinique in the manual.

Please take a look at our webpage for more. Www.Cybertronix.co.uk/quickscan
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Sat Oct 17, 2020 2:54 pm

Hi Stub,

So your using the blackbody as a reference point within the image or am I wrong in saying that?

Did you manufacture the blackbody yourself, if so can you elaborate on that process?

Thanks,
G
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Sat Oct 17, 2020 3:31 pm

Hey all, just a note. This is coming out soon.

https://twitter.com/groupgetscom/status ... 00/photo/1
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Re: Radiometric vs Non-Radiometric Leptons

Postby Stub » Sat Oct 17, 2020 5:53 pm

Hi,

Yes on both counts.

It is detected as a square object using blob detection. Preset as it stands to 37.8°C but this can be changed.

Uses an arduino with control software and a temp sensor, in the frame on the heated plate. A couple of buttons on the back allow temperature adjustment.

3D printed frame and electronics cover.

We can build more if useful...
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Sat Oct 17, 2020 6:26 pm

Hi Stub,

I appreciate your help on this matter. Do you basically use the following logic and say if the colour thresholds representing the blackbody @ 37.8 degrees is greater than the colour threshold of somebodies face then they do nothing otherwise trigger an alarm?

In my case I am not doing elevated skin temperature so I constantly need to find the hottest object in the scene and report that temperature, the temperature of the object would always be between 20 and 40 degrees. I just thought if I could make a blackbody relatively simply then I could drastically improve the accuracy of the Lepton.

Thanks,
G
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Re: Radiometric vs Non-Radiometric Leptons

Postby Stub » Sun Oct 18, 2020 3:37 am

Hi,

Yes that's exactly what I am using the black body to do.

However in your use case it would also work to dramatically improve the readings - I am getting +/- 0.3°C. Obviously you would be working over a larger range so won't be quite as good. You could scale the output around say 30° (ie set the blackbody to 30° and scale the pixel values accordingly so that the square is at 30 irrespective of the actual reading from the lepton.) You might have to play a bit to see what the best setting for the blackbody is maybe 40° would be better. I also use a Fluke temperature tester to check the black body temperature as it does take 15mins or so to heat up and stabilise.
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Sun Oct 18, 2020 8:15 am

Hi Stub,

In terms of the blackbody itself, are you using a solid state relay to control the constant temperature?
What material are you using for the surface out of interest, I know most metallic surfaces can be made into good emitters using paints.

I was actually thinking of having two black body sources in the scene, one at 20 degrees and one at 40 degrees so I would have the maximum amount of information available to me. That may have been overkill though.

Thanks,
G
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Re: Radiometric vs Non-Radiometric Leptons

Postby Stub » Mon Oct 19, 2020 4:20 am

Hi,

Yes I almost suggested two black bodies in my last reply.

We use a black coated steel plate, heater controlled with a FET. An SSR would do the same job.
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Mon Oct 19, 2020 4:34 am

Hi Stub,

Thanks for your help. I'm going to try create a blackbody myself as opposed to my current approach of improving temperature accuracy which was to alter the flux linear parameters on the Lepton and generate a calibration function which compared the output of the camera looking down at a container of hot water (due to its high emissivity) vs a DS18B20 temperature probe submersed in the water which I let cool from 50 degrees to around 10 degrees. I used that data to create a regression of camera output vs probe temperature which did improve the reported temperatures but not enough.

Kind regards,
G
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Re: Radiometric vs Non-Radiometric Leptons

Postby Stub » Mon Oct 19, 2020 4:43 am

Hi,

Excellent, good luck with that.

Cheers, Stub
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Re: Radiometric vs Non-Radiometric Leptons

Postby Stub » Mon Oct 19, 2020 6:41 am

BTW, nice looking thermal solution... Quick question. Not to worry if not, but I can't see a network port, would that be easy to add via the normal expansion? Or can we add the 5MP camera to the Portenta and use its wired ethernet from the OpenMV side?
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Mon Oct 19, 2020 6:50 am

Hi Stub,

Apologies, I have another question, what thickness is the steel you are using, you mentioned on your website it takes roughly 10 minutes for the temperature to stabilise. I'm not sure what way your blackbody works but I'm thinking of using a PID controller along with the SSR, a couple of cartridge heaters and a thermocouple to implement it as opposed to using arduinos or raspberry pi which may be more time consuming. Also given that set points shouldn't be changed in my system I don't think I will need much of an interface with it other than seeing the pv and sv which the PID controller would do.

I presume your previous post was not meant for me?

Thanks,
G
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Re: Radiometric vs Non-Radiometric Leptons

Postby Stub » Mon Oct 19, 2020 7:03 am

Hi,

Its a 3mm sheet. It would be good to know the results of your design and the dual black body...
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Mon Oct 19, 2020 7:08 am

Hi,

I'll definitely let you know if it works/if I get a chance to do it.

Thanks,
G
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Re: Radiometric vs Non-Radiometric Leptons

Postby kwagyeman » Mon Oct 19, 2020 1:00 pm

The OpenMV Cam Pure Thermal is just a mashup of everything we already support. Now with the Portenta we will support Ethernet. So, maybe we'll do a R2 with ethernet later. However, we literally used every I/O pin of the largest STM32H7 package. I think we can reclaim I/O pins by sharing I2C buses however.

Ethernet is tricky to support however. It can only be on certain pins... that conflict with other pins. Enabling it, along with SDRAM, LCD, and camera at the same time is hard.

...

There's the standard expansion shield interface for the OpenMV Cam on the Pure Thermal Board. The SPI bus on there will do 80 Mb/s. You can't add ethernet to that directly, however, you could add a wiznet to SPI IC. Or, add an ESP32 with ethernet.

...

Regarding the Portenta... we're talking with Arduino about making a high quality camera shield for it. With PoE Ethernet.
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Re: Radiometric vs Non-Radiometric Leptons

Postby Stub » Mon Oct 19, 2020 1:10 pm

Hi,

You have been busy! Thanks for the info. I will wait for the Portenta with the PoE and HQ camera shield. Not in a rush, just wanted to know how difficult it would be.
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Tue Oct 20, 2020 9:58 am

Hi Stub,

Another quick question for you, do you know what the power draw/usage is for the blackbody your using?

Kind regards,
G
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Re: Radiometric vs Non-Radiometric Leptons

Postby Stub » Tue Oct 20, 2020 10:05 am

Hi,

Yes its 20-25W or so.

If you do a 20°C version, will it be in a colder ambient temperature area?
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Re: Radiometric vs Non-Radiometric Leptons

Postby GL-ITC » Tue Oct 20, 2020 10:27 am

Hi,

The ambient temperature of the scene will probably fluctuate around 25 - 30 degrees for the most part but the outer limits are 20 and 40. Given space constraints both blackbodies would be relatively close together.

But to answer your question no the ambient temperature wouldn't/shouldn't be less than 20. 20 is the absolute minimum for the system.

Cheers,
G
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Re: Radiometric vs Non-Radiometric Leptons

Postby Stub » Tue Oct 20, 2020 11:02 am

And so what temperature will the 20°C black body be before you power it up?

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