Camera as an Analytical Light-Meter - Creative Uses of CHDK - CHDK Forum
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Camera as an Analytical Light-Meter

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Offline Barney Fife

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Camera as an Analytical Light-Meter
« on: 21 / March / 2008, 21:32:36 »
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« Last Edit: 22 / April / 2008, 14:34:09 by Barney Fife »
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Offline cybernut

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Re: Camera as an Analytical Light-Meter
« Reply #1 on: 21 / March / 2008, 23:41:30 »
Hi Barney

You never cease to amaze me!  You have contributed so much to the community by learning the intricacies of your camera and passing that info on in the forums and wikis to the rest of us.  I just have to give you a karma upgrade for all your hard work on that and your work on the forum itself.  Thanks...

Clive
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Offline zero01101

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Re: Camera as an Analytical Light-Meter
« Reply #2 on: 22 / March / 2008, 09:15:58 »
for real.
this is some prime knowledge.
thanks barney!
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Offline Barney Fife

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Re: Camera as an Analytical Light-Meter
« Reply #3 on: 23 / March / 2008, 03:04:21 »
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« Last Edit: 22 / April / 2008, 14:34:29 by Barney Fife »
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Offline ISO64

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Re: Camera as an Analytical Light-Meter
« Reply #4 on: 24 / March / 2008, 13:07:01 »
Chalk up one for Barney!

Did you ever try this?

Turn on your old ballast-driven fluo tube so that it is the only light in the room. Put a narrow piece of white paper against a dark background. Set your camera on a turntable and focus on the paper. Set WB while looking at this piece of paper. Then set exposure just about 1/2 ... 1/8 s, self timer delay to 1 s. Spin the table and luckily you will get a streak across the image, recording the oscillations in tube illumination AND change in colour output. Eye-drop picker tool in image processing will give RGB values.

ISO64

PS

Barney, is -1/3 EV set on your S3 to prevent image saturation?
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Offline Barney Fife

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Re: Camera as an Analytical Light-Meter
« Reply #5 on: 24 / March / 2008, 20:58:12 »
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Offline kwf

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Re: Camera as an Analytical Light-Meter
« Reply #6 on: 25 / March / 2008, 03:39:29 »
Very interesting Barney! Now what about a "Spyder mode" for CHDK? I just see a few principle problems ;)

i have the Spyder too, but i would not trust it too much. E.g. i noticed that for an TFT with enhanced color gamut was constantly calibrated to be a bit greenish. Uncalibrated these displays are even more greenish, but i think i can get it better calibrated with my eyes :)
So maybe the Canon camera is even better than the Spyder? ;)

I noticed this effect with some fluorescent lights (probably depends on the used phosphor), with bare eyes as well. Just looking quickly past the light and will show some colored "phantoms" of the light tube, similar to the "rainbow effect" known from DLP projectors. I even have seen this effect on some LCD TVs :(
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Offline Barney Fife

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Re: Camera as an Analytical Light-Meter
« Reply #7 on: 25 / March / 2008, 05:36:02 »
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Offline dvornik

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Re: Camera as an Analytical Light-Meter
« Reply #8 on: 26 / March / 2008, 00:24:34 »
The original Spyders were not accurate. The Spyder2 is accurate. Eye Ones and older Xrite DTP94 (that came with Monaco and were the most respected colorimeters on the market ) are accurate. Hueys are garbage.

Obviously how your monitor looks after calibration also depends on which targets you set for your calibration software in the first place.  You can set any target you want if your software allowes it.

One issue with LCDs is that in most scenarios (except some high end DDC-CI enabled setups) the white balance targets would be achieved by tweaking videocard LUTs - resulting in less than 256 values per channel.  So it's not surprising that the post-calibration results often look off-white and that it's hard to achieve a smooth greyscale gradient.

The main reason for using colorimeters, however, is not to make your monitor look different from what it looked before calibration (as a matter of fact it's often recommended to calibrate LCDs to their "native" settings - meaning just leving them as they are) . The main goal is to accurately measure the monitor output and convey this information to the color managed software via the monitor profile. The software (like Photoshop or Bibble or whatever) alters the colors it sends to the screen according to the profile information. It also forwards this information to the printer that has it's own profile. In that respect using a camera instead of a colorimeter or a spectrophotometer is utterly pointless.

I do see a possibility in measuring CD/M2 using a camera. Especially considering that most consumer-level monitors are set to some insane luminance levels (400? 500?).

Could you please post a link to that discussion?
« Last Edit: 26 / March / 2008, 00:48:10 by dvornik »
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databoy

Re: Camera as an Analytical Light-Meter
« Reply #9 on: 26 / March / 2008, 07:32:58 »
You may want to read this article regarding calibrating a Samsung SyncMaster 226BW LCD monitor.

http://www.behardware.com/articles/667-1/samsung-226bw-a-and-s-series-the-verdict.html
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