D405 and a Projector
Hello everybody, I am interested in combining a D405 (or two of them) with a projector to enhance depth recognition quality when scanning concrete surfaces, which are relatively homogeneous.
I have read https://dev.intelrealsense.com/docs/projectors#7-led-projectors and found the presented setup with a 3Watt LTPRHP3W suitable.
Could somebody who had done the same or ideally you, dear MartyG, elaborate on the specificities - such as the used wavelength (in my case apparently should NOT be IR, since there is a filter on the camera, but which one is better or was used in the Intel setup?), the objective (Resolution?) and the Pattern (was it "cloud of dots"? if so, there are at least 3 options currently: density 10.5%, 20% and 35 % - which one is better?)
I contacted the manufacturer of the projector, but they could not reliably identify the above mentioned things, so could you kindly provide info on that?
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Hi Dmitrii Sokolov The link below lists nm frequencies for each product (W, R, B, G) in the LTPRHP3W range.
https://machinevisionstore.com/catalog/details/1453
The model with a blue LED is 460 nm, green is 520 nm and red is 630 nm. Apparently the nm frequency of white LEDs can vary though. My research found different quotes for the nm range of white LEDs. Taking all the quoted frequencies into account, 400 to 600 nm seems like a safe estimate.
RealSense cameras can see visible light frequencies that are above 400 nm, so this particular range of projectors should in theory produce light that is within the camera's range of perception even with an IR Cut infrared-blocking filter equipped on the D405 camera. I cannot provide guarantees regarding performance though.
The higher the density of dots, the better it should be for depth analysis.
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Thank you MartyG for the detailed answer.
Since the scanning area is relative small 15 per 15 cm or even less, I guess 3 Watt will be more than enough even if some of light lies beyond the range of the D405. So I guess I will go with a white one.
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Hi Dimitrii! (& MartyG)
Assuming you have bought the structured light projector or pattern projector in white, how has the performance improved? We have tried with sharp flood leds at an angle (as a gradient is still a texture) and performance has already risen considerably we are also considering a pattern projector to simplify this angled light requirement. Please let me know your experience with the same - our application also requires just 3 Watt white SLP.
MartyG are there any others in your experience who have used a projector with the D405 to achieve improved performance? I am currently using angled light + High Accuracy (Our objects do have a lot of untextured areas) and performance is considerably higher (we are getting sub-millimeter accuracy). We still have some false depths due to non-textured surfaces at certain angles which we hope an SLP can solve. What do you think?
Thanks!
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Hi Rohan A I have recommended the use of a visible pattern projector with the D405 camera model (see the link below), as this camera model cannot see invisible infrared projections due to being equipped with an IR-blocking IR Cut filter. However, I have not had reports from RealSense users who have tried it.
https://dev.intelrealsense.com/docs/projectors#6-the-consumer-front-projector
Adding an additional projector at a different position if possible to do so can help to cover blind-spots in the first projector's projection. Where patterns from different projectors overlap, the increased pattern density can be beneficial for depth analysis of the surface where the overlap occurs.
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Hi MartyG!
Thanks for the information. On the other hand is it possible to know where the IR cut filter coating has been performed - directly on the lens or on the glass components of the module? Is there an easy way to remove them? We also have the D415 and 455, but none come close to the minimum depth requirements we have. If we can remove the IR cut filter it would be the best case scenario. Please let me know if this is even possible - we do have the means and machinery to modify it if required.
Thanks
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The IR-Cut filter is listed as part of the infrared sensor component on the D405's camera circuit board, indicating that it is not likely to be removable without damaging the sensor.
I know of only one case in RealSense history where lenses were successfully removed by a RealSense user without damage, and such a modification would likely immediately invalidate the camera's warranty. So I would not recommend attempting it unless you are confident in your ability to do so and can afford to write the camera off if it becomes broken.
If the minimum depth range of your project is not less than 10 cm then the D435 model might suit your needs because of its smaller minimum distance than D415 and D455 and lack of an IR Cut filter (or any other type of filter) on its sensors.
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Hi MartyG!
Thanks for the information. Unfortunately, we require a minimum depth as close as 5-7cm (Achievable with disparity shift on D405).
Could you please share the support thread of the case of removal of the IR cut filter from the camera (I am unable to find it Googling)?
Further, apart from using the LED projector recommended, DLP was hinted at on the page about projectors for D4XX (https://dev.intelrealsense.com/docs/projectors ). Have you come across someone successfully using a DLP (from Texas Instruments - Digital Light Processing) as a structured light projector? I am hoping we can swap out the DLP's backlight for a 780-800 nm one, which is under the IR cut range but barely visible.
Thankful for your help
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The old support thread regarding lens removal is below, though it does not provide details about the procedure that was used to do so.
You may be able to find some useful search results about DLP and structured light if you google for the exact search term below, including the quotation marks to ensure relevant results.
"dlp" "structured light" "texas instruments"
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Hi Rohan A
I plan to implement the exactly the same (white visible) projector as used in the whitepaper from Intel. I have not ordered it yet, but quit close to it. Firstly, I had to clarify things related to the appropriate optics - I wanted to install the Projector relatively close to the object (less than 100 mm away), so I will still have a projected pattern with a higher spatial resolution. And the company is still checking if there are lenses that they can offer for such a close-range distance. I do not consider removing the IR Cut Sensor since this will bring me nothing.
Btw MartyG can you elaborate on that, if that is really make sense to bring the projector closer in case of D405?
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Hi, @Dmitrii Cutting the IR sensor might be useful because one can then use Near IR or IR laser-based SLP which is nearly the same cost if not cheaper compared to the LED-based SLP while also having the benefit of not affecting the RGB readings. But I am sure you must have considered it and fallen back on an alternative SLP. Have you looked into Texas Instruments' DLPs - seems very promising.
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Hi Dmitrii Sokolov I do not have information about visible pattern projectors beyond what is in the projector guide and so I cannot make guarantees about performance. In general though, having the camera closer to a visible pattern projected onto a surface should be beneficial as the camera would be better able to see the texture that the projection gives to the surface. More texture = better depth analysis.
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Rohan A In my case RGB readings practically do not bring any value - I work with depth images and looking for ways to increase accuracy of them while capturing wet concrete which sometimes may have low texture or be reflective. Reflection is another problem though, I am just lucky that is not so prominent in my case (yet!! will see what material comes next). Laser Projectors have speckle - this I see as a major problem, and with our distance the lasers do not bring much benefits since we do not need much power.
I just looked quickly at DLPs - that is smth that I have never worked with - looks interesting, apart from that I cannot say anything else. Worth trying though, depends on the price. The projector that I consider is also not super expensive - around 1100 EUR with optics and pattern included). Which is not cheap, but kind of affordable. Especially if you know Intel Engineers tried that and it helped. I would love try smth else though if I would have more time :) So very excited hearing back from you if you decide for DLPs.
@MartyG I would like to bring the projector closer to the object, (not only the camera) and hope, that this way I will achieve a higher density of projected texture and thus a better depth image quality
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Hello everyone, I have exactly the same problem as you. I would like to improve the accuracy of my D405 camera in presence of untextured surfaces.
First MartyG what would give the best surface quality: the D405 + projector at 8 cm or the D435 at 30 cm? In the two case I have to buy something but I would like to do the right choice.
Also Rohan A you mentioned "I am currently using angled light + High Accuracy" what is this "high accuracy" you are talking about ?
Finally, Rohan A and Dmitrii Sokolov if you have some results of your setup or any advices that I should know to do the same as you, I would be delighted to see this.
Thanks for help -
Hi Cuau Lenaic If you are going to be using the camera with a range of different untextured surfaces then a D435 and its built-in dot pattern projector should give the best chance of consistent success. I could not guarantee that using a visible pattern projector with a D405 would provide consistent results across a range of different untextured surfaces.
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