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Signal to switch on and off external illumination

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Re: Signal to switch on and off external illumination

Postby illustrami.com » Wed Jan 23, 2013 4:20 pm

Of course all this my last post is written not knowing many and many things that can chage the scenario, for example that the ccd/cmos sensors might be more or less sensible to one wavelenght or another, that ccd is different from cmos, so it might work differently depending on the sensor, and so on

Ideally I guess a panel giving at max power almost the same output for each channel, and with each channel adjutable with a dimmer might be the best solution for all cases, one have a panel that can be used for anything then (in the very special model we can add also UV LED so one can get a tan too now and then :D ).

Davide
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Re: Signal to switch on and off external illumination

Postby illustrami.com » Thu Jan 24, 2013 9:10 pm

Hi Walter

I was reasoning again about the way David take the snapshots, the iris is fixed at the value that is good for the scanning process, David do not control automatically the iris (maybe on the cameras of future??), so the iris value was set at calibration time in the former phases of the process

Thus in the texture grabbing panel one can only change the exposure time and the intensity of light, from now on we know that can be the projector or the external panel, this to have the best image on screen, then David does the calibration of the white balance, it is in this point that I do not know what happens!!!

What does David ???
I do not think that changes the exposure time for each colour, I guess that having as a reference the white panel it scale the luminance of each channel in order to balance them so to get the white point or the neutral one.

In ol' good days when white balancing using film the matter was to correct colours shifting of the light with filters, filament tungsten gave too much of yellow, ordinary neon too much of green, pressurised lamps could give too much orange, blue... and so on but most of the cases there could be endly also a subtle shifting due to the mix of all what was used or present and not removable, this was not really simple as today.

Today virtually one do what ever want, then take a white thing, place it in the light that will be used point the object with the camera and then click on the magic button "white balance", when using a complex system sets some parameters too... with digital system the illumination must be ready with filters set up before doing the white "point", with film you need to create white light prior to shoot anyway but it is physically a mix of wavelengths that give the "white" (depending on the film used)

During balancing the goal is to scale the luminance of each channel in order to have neutral objects appearing as neutral and not colour cast (shifted), once this is achieved the other colours should be quite fine, Viggiano's method is known to be the most useful.

Viggiano also say what I suspected, it is better to grab the best shoot possible in the beginning as manipulate it later does not give best results achievable.

From wikipedia
Viggiano found that white balancing in the camera's native RGB tended to produce less color inconstancy (i.e., less distortion of the colors) than in monitor RGB for over 4000 hypothetical sets of camera sensitivities.[8] This difference typically amounted to a factor of more than two in favor of camera RGB. This means that it is advantageous to get color balance right at the time an image is captured, rather than edit later on a monitor. If one must color balance later, balancing the raw image data will tend to produce less distortion of chromatic colors than balancing in monitor RGB.


Still this does not necessarily mean that David cannot balance the colours if the light have different intensity for each one, but in principle I guess that can do a much better work if it finds similar intensity values.

Apart that I guess that when the light is much less as the iris cannot be changed on the fly the image might come out too poor on the weaker channel side this will be reflected in the overall quality of the image.

I am very curious to know if I am wrong or I got it, I just do not know, I am not fond at all in details about the whole matter, I am sort of blind walking into.....

Bye
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Re: Signal to switch on and off external illumination

Postby WalterMo » Fri Jan 25, 2013 5:38 pm

Hi Davide,
Certainly you are right and the luminosity of the three colours should be preferably the same. On the other hand the intensities of red and blue of the sun light are only about half the intensity as green:
http://www.google.de/imgres?imgurl=http ... Ag&dur=499

It should be no problem to adapt it. I can try it by assembling a different number of single 3W LEDs, each for its separate colour. Here I found them for a reasonable price:
http://www.highlight-led.de/bauelemente ... s_c447.htm

They have: Red = 80 lm, green = 130 lm and blue = 45 lm. So I could use: 3 x green = 390 lm, 3 x red = 240 lm and 5 x blue = 225 lm.

And then I would arrange them on a ring, surrounding the camera's lens. In so doing the panel can illuminate the object without producing shadows. What do you think?

Walter
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Re: Signal to switch on and off external illumination

Postby illustrami.com » Tue Jan 29, 2013 12:25 pm

Hi Walter

Well the guy in the blog adsorbed all my attention, very interesting, but then suddenly he wrote:
"As a result, we (and again, our cameras) need to be able to adapt to these constantly changing spectra." VERY GOOD.. THEN??? :?: " And that’s exactly what I’m going to discuss — next time. Until then … Happy Shooting!" :lol:

I did not know the spectral composition of visible sunlight in details, I surely have seen it decades ago at school, but now I have just a general knowledge about.
This is very interesting tough.

Please take my words as in free reasoning, as I might be wrong now and then, I just say my opinion and stimulate answers, researchs, discussion and eventually help to get solutions.

My worry for which I wrote so is not much about the colour mix but about the exposure and having the chance to have a good snapshot anyway, whatever is there in front of us..., so to have similar luminance levels and being able to adjust them is the best thing I guess.

This is the main reason for which ideally I'd like to have an universal instrument that allow to do it all whatever we have there we can try to find a solution adjusting levels with the dimmer, diffusing light with filters, doing colour balance and seeing the results.

Your idea to have the ring to apply to the camera is perfect, most shadows are gone then, but still some borderline shadows will be there I suppose.

I'd suggest that the system should be modular, so one can adapt the system to what needed and to what can afford or what suffice in different situations.

In normal photography sets shadows are not necessarily bad, in may cases are avoided too anyway.

In our texture photography set I guess is much better to have a uniform plain photography with radiose illumination and no shadows at all, the object with coloured texture will be used in a CAD for rendering, so shadows and illumination will be set artificially within this system, therefore preformed shadows are unwanted and theoretically is absent best rendering results can be achieved.

In this respect I do not know how much the backlit illumination is going to enhance the texture or on the contrary to create burnt areas in the final result, this is to experiment. By the way a think that a basic illumination set can have more light panels to make sure all spots of the object are evenly illuminated and shadows virtually eliminated or extremely weak.

So if the system have connectors to connect additional panels in a cascade at wish (or array, it's the same) one can build the perfect system for its own necessities.

I guess that normally one want at least 3 or 4 panels (or even more depending on the scene dimensions) to inundate the scene with light from several corners and have one backlit

Thank you
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Re: Signal to switch on and off external illumination

Postby WalterMo » Thu Jan 31, 2013 6:58 pm

Here we have my first external controlled RGB illuminator.
It consists of 90 power Leds, 30 for each colour. I bought them on stripes á 30 Leds. Here is the link for the green one:
http://www.pollin.de/shop/dt/NDA0OTc4OT ... gruen.html

The stripes could be easily cut in parts á 6 LEDs and as you can see I have placed them radially on a disk. The camera lens is in the centre of the disk. I hope due to this postion the shadows on a texture will be minimal. And the illuminated area is really homogenous and white.
An Arduino Uno receives the signals r, g, b and s (for black) via USB from DAVID and controlls 3 MOSFets, each for one colour.

First SL tests with the new version 3.7.0 beta and a monochrome camera were already made. And it works! More will follow.

Walter
Attachments
RGB Panel2.jpg
Photo taken by a reduced luminosity of the LEDs and by a 500W lamp illumination.
RGB setup2.jpg
The setup
RGB area.jpg
Homogeneously illuminated area. Photo taken without white balancing!
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Re: Signal to switch on and off external illumination

Postby illustrami.com » Mon Feb 04, 2013 6:53 am

Great Walter

I am admiring you for the fast action and results.

I look forward to see the results on the scans

Bye
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Re: Signal to switch on and off external illumination

Postby WalterMo » Mon Feb 04, 2013 10:48 am

Here are the first results made by the RGB illuminator. As an object I have scanned a colourful cocoa box. I think it has all the main colours printed on.

The attached screen shots show from left to right:
Texture only made by the projector's light, texture only made by the RGB illuminator and the third image is a mix of projector and RGB illuminator.

To enable an illumination only by the external RGB source I have shifted the projector slider in DAVID to its minimum. (Of course only for grabbing the texture).

You see that the colours, generally speaking, are OK. But the brightness of the RGB illuminator is rather low. This doesn't depend on the luminosity of the LEDs. Before the texture is grabbed the brightness of the camera image is adapted (adjusted) by the mechanical aperture at the camera lens.
And this brightness was the same for projector and RGB illuminator.

I think the reason could be a delay when the Leds are switched on and off. During adjustment all LEDs were continuously switched on. But what happens if the camera capture times for the three colours and the Led-on times don't overlap perfectly?

Walter

PS: The tests were made with an Acer K11 projector and the DAVID monochrome CCD camera.
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Drei Arten zusammen.jpg
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Re: Signal to switch on and off external illumination

Postby Sven » Mon Feb 04, 2013 12:02 pm

Hi Walter,

I don't quite understand, how did you do the White Balance?
You should place something big and white in the scene, then:
1. Go to Texturing Menu
2. Set Projector Brightness to 0
3. If possible, switch on all LEDs and if the images is very dark, adjust the camera Exposure so that you get a good image
4. Start White Balancing

Then the White Balancing (which includes some "brightness balancing") should be adjusted correctly.

Sven
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Re: Signal to switch on and off external illumination

Postby WalterMo » Mon Feb 04, 2013 1:21 pm

Hello Sven,

White Balancing was each time done before grabbing. But I had not placed an additional white object in the scene. I thought the white wall paper in the background would be sufficient (see the two screen shots after scanning). And for the projector illumination it works.

Walter
Attachments
Both scans with background.jpg
Left: Scan with projector illumination, right: with LED illumination
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Re: Signal to switch on and off external illumination

Postby Sven » Mon Feb 04, 2013 5:42 pm

White Balancing requires a white object. ONLY a white object. If you do it with a yellow object in the scene, this can influence the result, maybe that is why your background is a little blueish.
I don't know why the 2nd image is so dark.
The white balancing has a limitation, it will increase each color channel max by factor 6.
Please take a look at your Advanced Settings -> Texturing, there you can see which factors the White Balancing has computed. They should be between 1 and 3. If they are much higher (max. 6) then you should increase the image brightness (best: exposure time), then start White Balancing again.

Sven
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Re: Signal to switch on and off external illumination

Postby illustrami.com » Wed Feb 06, 2013 11:47 am

Hello

The results despite the look of the snapshots are very good

The burnt on the right corner side is due to lack of diffuser, some lack of ligh is due to the "One panel setup" which will never be sufficient alone to do the job

Once a 4 panels cluster setup (or more panels) is used this pictures will be of superior quality

As Sven wrote the white balance must be done on a full white screen evenly illuminated , best to use a clean plain mat white sheet and place it in front of the camera in a way that onscreen all the pixel are of the same color, it will not be really easy to do it unless a large enough sheet is used.

Once a good white balancing is done I am very confident that the images will be very good and the better is done the illumination the best will be the results.

David does a very good white balancing , so there should no problem to reach superior quality levels, over what already achieved, which is not least at all.

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Re: Signal to switch on and off external illumination

Postby VDX » Wed Feb 06, 2013 11:56 am

... how is the 'white balance' performed with a BW-cam and coloured illumination?

My idea was to take snapshots with the different colours and then average them by adjusting the specific alpha-channels afterwards, so a white part will be as white as possible?

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Re: Signal to switch on and off external illumination

Postby illustrami.com » Wed Feb 06, 2013 2:31 pm

Hi

This is performed By David LaserScanner analysing the 3 B/W shots illuminated each with a "pure " red, green, and blue light (which using LED technology is really almost only of the right wavelength)

It is an algorithm, so many simple operations in a ordered process, basically many calculations are done to determine the colour of each pixel of the 3 shots which report much information about the colours even if are in B/W when illuminated with a light which wavelenght is known.

BTW the same thing is done by any colour camera, maybe in different ways but upon same principles, it is done in the embedded dedicated CPU unit of the camera with a similar embedded software, meanwhile with David is done externally using an ordinary PC (which enormously more powerful and does even much much more, could elaborate thus further the image and does other things in the meantime)

You can always further manipulate an Image but as demonstrated by Viggiano you achieve best results only when the original shot is taken in the best possible conditions, all post elaborations of the image are likely to output a result that is never as good as a perfect original shot.

From Wikipedia
Viggiano found that white balancing in the camera's native RGB tended to produce less color inconstancy (i.e., less distortion of the colors) than in monitor RGB for over 4000 hypothetical sets of camera sensitivities.[8] This difference typically amounted to a factor of more than two in favor of camera RGB. This means that it is advantageous to get color balance right at the time an image is captured, rather than edit later on a monitor. If one must color balance later, balancing the raw image data will tend to produce less distortion of chromatic colors than balancing in monitor RGB.


Of course when the original shot is not good or not optimal post elaboration can give better results.

Bye
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Re: Signal to switch on and off external illumination

Postby WalterMo » Thu Feb 07, 2013 6:22 pm

These scans with texture were made as Sven advised above.
Means for the white balancing I have put a large white pasteboard in the scene. And now it looks much better. The brightness, if illuminated by LEDs, hasn't quite the same intensity as illuminated by the projector but the colours are nearly true. The colour of the corner walls in reality isn't really white, it's a bit beige. Only the two small specks, on the left wall and on the right wall just below the can are really white (it's TippEx). And of course the white on the can is white. :wink:

I am really astonished how true a texture can be made by a monochrome camera.

Walter
Attachments
Texture by Proj illumination.jpg
RGB illumination by projector
Texture by LED illumination.jpg
RGB illumination by LEDs
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Re: Signal to switch on and off external illumination

Postby illustrami.com » Sun Feb 10, 2013 5:04 am

Hi walter

That is already much better

Analysing the previous small previews I believed that the colour are more realist with the LED, so if I understand well you confirm it.

The burns are noxoious, the direct light beams of the LED produce them (they have a lens to diffuse the beam but still is a quite definite cone, menwhile from the projector the light cone is composed by many little cones of equal intensity)

As a fast diffuser you can try to use a sheet of the typical transpearent paper once was used for layer drawing on blueprints

Or you can use a diamond textured plastic cover of a neon light, also regular soft paper for kitchen use is going to work, but actually is too heavy and a very strong source of light would be needed, but often the very fine adsorbing kitchen paper sort is a 4 layers pack, peeling one single layer of a paper handchief might do cheap trick as a fast test.

Otherwise in a good photography shop they might sell you or just hand out a sheet of profi diffuser paper (which works best)

Diffusers are necessary, then just adding also more diffused light panels from more sides complete the set up.

In this way should be possible to build up a perfect looking model with an astonishing good textures without much post elaboration, this is going to save hours of work on complex projects.

Cutting properly partial meshes and editing the meshes is already possible to create almost perfect models, once this panels are used should e possible on the spot.

Bye
David
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