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Author Topic: DCamProf - a new camera profiling tool  (Read 767316 times)

Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #560 on: June 16, 2015, 12:54:58 pm »

does it mean that you were illuminating some surface (like styrofoam) and measuring off the reflected light ? or something else ?
Matt spectralon panel. That gives much better idea of the beam profile.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #561 on: June 16, 2015, 12:58:44 pm »

How could the spectrum be spiky? Shouldn't it be physically impossible when you have halogen? As far as I understand the Solux is nothing else than a standard halogen lamp with a blue-filtered reflector.

Indeed, you really need a variable power supply to get a color temperature you want. It's graded to 4700K but far from all lamps reach that, halogens vary quite a bit naturally and I would not think they have put 4700K in the center of the normal distribution. Lamp fixtures also seem often seem to underpower the lamps bit, and then with an unsuitable lamp shade (especially if using the unpainted older lamps) you lose even further due to mixing in unfiltered light.

I'd be surprised if Solux halogens would drift more than any other halogen, as it is a, well, halogen lamp.
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #562 on: June 16, 2015, 12:59:55 pm »

what might be the source of the drift then... assuming that you have some lab grade power supply and voltage then can be assured within what ? like < 0.1% or something like this ?
Possibly, accelerated aging; or overheating. Anyway, Solux are using Eiko Q50MR16/CG/47/36 neodymium bulbs, and metal-doped filters produce not very natural SPDs.
« Last Edit: June 16, 2015, 01:33:07 pm by Iliah »
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #563 on: June 16, 2015, 01:00:51 pm »

> How could the spectrum be spiky? Shouldn't it be physically impossible when you have halogen? As far as I understand the Solux is nothing else than a standard halogen lamp with a blue-filtered reflector.

If you look into how the reflector is made...
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #564 on: June 16, 2015, 01:07:46 pm »

I only have the Colormunki instrument to measure with that claims 3nm at high resolution mode, no spikes turn up there (spikes do turn up very clearly on a fluorescent source for example).

This makes me think that even if there are spikes they are narrow enough to have negligible impact in camera profiling applications. What we're measuring in profiling is the camera's spectral integration, and a "worried" spectrum is no problem unless it risks shifting the energy to such an extent that it shifts the integration result. Wouldn't you agree?
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #565 on: June 16, 2015, 01:16:07 pm »

Additionally, it seems to me that a typical photographic flash or xenon arc lamp would be worse concerning spikiness, and certainly shot-to-shot variation, here an example flash spectrum (wavelength is in Angstrom not nm, divide by 10):



I'm just presenting the "evidence" I base my own recommendations on. As I thought I had enough info on my hands to be able to recommend the Solux on overdrive as a D50 simulator for camera profiling, any claims that suggests that it's actually no good is very interesting to me.
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #566 on: June 16, 2015, 01:24:43 pm »

> a "worried" spectrum is no problem unless it risks shifting the energy to such an extent that it shifts the integration result.

I simply found that the results of colour transforms I'm getting with 5000K using normal filters over halogen lamps are better compared to Eiko/Solux, and I can use regular 3200K halogen lamps and cheap high quality filters; both components easily replaceable. And I do not need to deal with uneven distribution of CT across the beam.
« Last Edit: June 16, 2015, 01:32:51 pm by Iliah »
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #567 on: June 16, 2015, 01:26:34 pm »

I only have the Colormunki instrument to measure with that claims 3nm at high resolution mode, no spikes turn up there (spikes do turn up very clearly on a fluorescent source for example).

This makes me think that even if there are spikes they are narrow enough to have negligible impact in camera profiling applications. What we're measuring in profiling is the camera's spectral integration, and a "worried" spectrum is no problem unless it risks shifting the energy to such an extent that it shifts the integration result. Wouldn't you agree?

a small note... for example CMF that you feed into DCamProf being spiky does not affect much the profiles it generates...
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #568 on: June 16, 2015, 01:52:54 pm »

Ok, thanks for sharing.

I just did a quick drift test when running it 15.8 volts at 5500K. It's not free from drift, the first 10 minutes (started cool) it drifted about 0.3DE, but when warm it seems to stabilize a bit and it drifted 0.08DE the following ten minutes (plot attached). That drift is so small it can be some related to measurement too.

Anyway, I'm going to recommend to work with lamps that's been on for 10 minutes or so, and then work relatively swiftly, should take only 5 minutes or so to complete a series of test target shots, and it that time it should be stable enough.
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #569 on: June 16, 2015, 02:01:39 pm »

> I'm going to recommend to work with lamps that's been on for 10 minutes or so

Usual is 15 minutes to 20 minutes. Now, after the bulbs are stabilized, one needs to measure the spectrum; and that defeats the purpose of having D50 simulator. To be clear, that is the case with any halogen bulbs except lab grade sources, and even with those it is still better to measure the spectrum. Point of the exercise is to get as close to 5000K blackbody as possible the cheapest way.
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #570 on: June 16, 2015, 02:12:08 pm »

Usual is 15 minutes to 20 minutes. Now, after the bulbs are stabilized, one needs to measure the spectrum;
one might imagine a spectrophotometer used may be in ambient mode right when you shoot your target... for example make a hole behind something where you target is mounted to place spectrophotometer there... now you just need to sync things somehow.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #571 on: June 16, 2015, 02:41:22 pm »

My strive for a "D50 simulator" should not be taken too literally, the purpose I have is a smooth spectrum, no significant broad peaks or dips, no significant spikes, with an overall distribution similar to D50. For camera profiling there's no real value in exactly matching D50 as D50 doesn't really exist in nature either. The purpose of this is to have an alternative to going outside using actual daylight. Shooting glossy targets with minimized glare is a lot easier to do with this type of light source than using real daylight.

Now I'm pushing it to 5500K to get a little bit more spacing from 2850K in a dual-illuminant scenario.

Compared to a 3000K halogen lamp with an 80B filter all indications I get is that the overdriven Solux makes a better job. I'm sure though that Liu labs lamp is even better, but I doubt it will present any significant gain, except if we want to get closer to 6500K which the Solux can't do.

It's far from a practical setup, I have only one lamp, flatfield correction is required, temperature stabilization is required, it's preferable to measure it. I wouldn't use this for copy work or anything like that, but to shoot a target with flatfield-capable software it seems to be a good setup.

The value of actually measuring the spectrum is there when we want to make a DNG profile that can do precise whitepoint estimation, otherwise it's not that important when we make a generic "daylight" profile.
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torger

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Re: DCamProf - a new camera profiling tool
« Reply #572 on: June 17, 2015, 02:08:03 am »

On a different subject; I'm going to have to look more into how to subjectively deal with the contrast curve. The global desaturation trick did not work out as well as it first seemed, it may work for highly saturated colors but leave low saturation colors too desaturated. Possibly an increasing onset depending on saturation would work, or I need to figure out some different strategy.
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #573 on: June 17, 2015, 04:27:55 am »

I simply found that the results of colour transforms I'm getting with 5000K using normal filters over halogen lamps are better compared to Eiko/Solux, and I can use regular 3200K halogen lamps and cheap high quality filters; both components easily replaceable. And I do not need to deal with uneven distribution of CT across the beam.

Iliah, do you use 80A, 80C Lee gels for correction? I had a go with Lee CT blue gels (full and half) briefly and for my halogen source they do add strange dip at the green area. Have not evaluated various lamps yet only the one that came with my source but it does not have this without filters.
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #574 on: June 17, 2015, 09:22:03 am »

Iliah, do you use 80A, 80C Lee gels for correction? I had a go with Lee CT blue gels (full and half) briefly and for my halogen source they do add strange dip at the green area. Have not evaluated various lamps yet only the one that came with my source but it does not have this without filters.
I use 8x series.

For the lights they make:
Lee 283, 201, 281, 202 (these are the main ones)
Given the sensitivity of sensor green channels, a dip in the green area may be a good thing.
 
for use with MR16 and PAR bulbs, framed glass, better greens:
Lee B64, LD201, LD202
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Alexey.Danilchenko

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Re: DCamProf - a new camera profiling tool
« Reply #575 on: June 17, 2015, 09:31:40 am »

I use 8x series.

For the lights they make:
Lee 283, 201, 281, 202 (these are the main ones)
Given the sensitivity of sensor green channels, a dip in the green area may be a good thing.
 
for use with MR16 and PAR bulbs, framed glass, better greens:
Lee B64, LD201, LD202

Thanks, mine was 201 (Full CT blue) that had this dip. I tried 202 as well and it was a lot better and smoother. For now my only use for them was an attempt to even slightly blue areas of the spectrum for monochromator input hence the questions.
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #576 on: June 17, 2015, 09:33:39 am »

Thanks, mine was 201 (Full CT blue) that had this dip. I tried 202 as well and it was a lot better and smoother. For now my only use for them was an attempt to even slightly blue areas of the spectrum for monochromator input hence the questions.
Lee are publishing pretty accurate Y-curves on their site.
For the purpose of making the light to monochromator more even I would be looking at 281 and 202, maybe double layer.
« Last Edit: June 17, 2015, 09:36:07 am by Iliah »
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #577 on: June 17, 2015, 09:39:20 am »

Lee B64, LD201, LD202
those who love smooth graphs shall like this one = B53 Blue 3 - it is a black line on the graph

« Last Edit: June 17, 2015, 09:43:03 am by AlterEgo »
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Iliah

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Re: DCamProf - a new camera profiling tool
« Reply #578 on: June 17, 2015, 09:58:56 am »

those who love smooth graphs shall like this one = B53 Blue 3 - it is a black line on the graph


With dichroic filters, the curve is angle-dependent. If the sampling is closer, such filters usually show the transmission curve is not very smooth https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=986
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AlterEgo

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Re: DCamProf - a new camera profiling tool
« Reply #579 on: June 17, 2015, 10:08:25 am »

With dichroic filters, the curve is angle-dependent. If the sampling is closer, such filters usually show the transmission curve is not very smooth https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=986
but then @ any angle that curve shall be still smoother than others, because it has a better "starting point /at 0 degrees/", no ?
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