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Author Topic: DSLR testing sites like DXOmark and Imaging Resource use HMI and LEDs for color  (Read 18655 times)

Tim Lookingbill

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Need to make a correction on the Ottlight. I meant to say that I didn't get a match to what it was suppose to look like under normal white light because the Ottlight made warm colors appear more saturated but at least I got a match on my display of this saturated color.

I ran into a brick wall with the Soraa and French's Mustard bottle. First time I've ever seen this.

Here's the image I've posted before of the Ottlight compared to the Solux 4800K. The Ottlight makes the deck of cards too clean and new looking. The Solux reproduces it exactly like it appears to me.
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digitaldog

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Danger Will Robinson, someone here is Lost in color space.  ;D
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Andrew Rodney
Author “Color Management for Photographers"

digitaldog

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Not with all colors if one wants an exact match especially with paintings in combination with the lighting viewed under. I've had the same issues with the 6 pigment phosphor technology of the 5000K 95CRI Ottlight 100wt HD CFL but at least with that I could generate a color match on my display with common objects like an old deck of cards, OB paper but I didn't have the French's Mustard bottle at the time.

And that's really been my main point which is there needs to be a broader choice of color targets when using any brand of lighting with fine art painting repro both artificial and natural. Just because someone comes out with a brand new wizbang full spectrum artificial white light and it measures perfectly with some spectro it doesn't mean it's going to reproduce exactly all possible paint formulations used in paintings.

It might even look great as a fine art painting viewing light but not necessarily be ideal for capturing and processing digitally what we see in combination with the light and the painting.
Read, learn:
https://blog.kasson.com/the-last-word/metameric-failure/
http://www.colorwiki.com/wiki/Metamerism_Article
http://www.johnpaulcaponigro.com/blog/234/metamerism-metameric-failure/
https://www.homecinemaguru.com/metameric-failure-in-display-color-calibration/
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Andrew Rodney
Author “Color Management for Photographers"

Manoli

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https://www.homecinemaguru.com/metameric-failure-in-display-color-calibration/

Interesting ..

“ Forbidden - Visitors from countries outside of North America are not permitted to browse this site because of changes in European privacy laws.”
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digitaldog

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Interesting ..

“ Forbidden - Visitors from countries outside of North America are not permitted to browse this site because of changes in European privacy laws.”
Weird! Pretty good display centric piece on metameric error but plenty of good in the others.
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Andrew Rodney
Author “Color Management for Photographers"

Tim Lookingbill

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Interesting ..

“ Forbidden - Visitors from countries outside of North America are not permitted to browse this site because of changes in European privacy laws.”

Wonder if that explains DigitalDog.net script among other tracker indicators showing up in the lower left corner of Firefox browser. I'm getting tired of all these scripts slowing my downloading something as simple as a web page with the indicator "waiting to connect"...xxx whatever.
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digitaldog

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Wonder if that explains DigitalDog.net script among other tracker indicators showing up in the lower left corner of Firefox browser. I'm getting tired of all these scripts slowing my downloading something as simple as a web page with the indicator "waiting to connect"...xxx whatever.
More assumptions, this time outside the realm of color. Hole 3 feet deeper.
Got Safari bud? Runs fine, gets to that site. But start with Jim's article although JP's is probably maybe aimed at your level of understanding.  :P

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Andrew Rodney
Author “Color Management for Photographers"

Tim Lookingbill

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I'm not assuming. I can see your script with your name on it, Andrew.

LuLa loads quite quickly for me. I just don't like seeing scripts in general because some do hang for awhile waiting to connect. Google now does this which is my home page and now I've switched it to "The Fastest Loading Page On The Internet". https://varvy.com/pagespeed/wicked-fast.html

I'm going to take advice from the IT specialist on that site before I take advice from a Color Management Consultant.
« Last Edit: June 29, 2018, 07:53:53 PM by Tim Lookingbill »
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digitaldog

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I'm not assuming. I can see your script with your name on it, Andrew.
I'm going to take advice from the IT specialist on that site before I take advice from a Color Management Consultant.
It isn't my script. Just like I didn't process any image here, of mustard bottles or anything else.
You don't take advise from color management experts so I can't fathom you'd find then take advise from an IT specialist either.
All I did was copy and paste a URL from a site I can navigate to, as the screen capture proves. Don't go there, it is likely over your head anyway. Start with JP's piece, then Jims, see if can connect the dots such you begin to understand issues with color matching and illuminants. Or don't.
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Andrew Rodney
Author “Color Management for Photographers"

Alexey.Danilchenko

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As for the light sources - I am about to submit all of that (having tested all the LEDs to death now and finishing Xenon pulsed light source testing) but it will take me a few days to finish write ups. Hopefully will be on GitHub by the end of upcoming week.

All submitted to GitHub now - the hardware (and mostly firmware) part of the project is complete now.

But soldering surface mount components is difficult. ... Ditto with fabricating COB mounting plates and heatsinks.

LED light source as well as some details of constructing LED COB head are on this page if you are interested
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Jack Hogan

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Horrors: the actual label, which under a loupe does show a dot pattern, is just outside sRGB color gamut. Which is why I don't suggest ENCODING raw captures into sRGB!
OK, done with Mustard and issues of color gamut of French's for those who insist on using sRGB.
Lab values of label is 85.07/14.31/96.50   

Interesting.  That Lab value is also outside of AdobeRGB from illuminant A to D65 with 2 deg CIE XYZ observers.  What observer did you use in your conversion?
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Jack Hogan

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All submitted to GitHub now - the hardware (and mostly firmware) part of the project is complete now.

LED light source as well as some details of constructing LED COB head are on this page if you are interested

Excellent Alexey.  How about adding some images of the light as set up for its intended purpose?
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Alexey.Danilchenko

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Excellent Alexey.  How about adding some images of the light as set up for its intended purpose?
Sorry not quite following the question. The light head mounted to face monochromator entry slit at a distance that keeps light in a small condensed circle. Nothing special around that especially since monochromatots do differ. I'll eventually post photos of all my setup and some details about construction but not yet.
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Iliah

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> How about adding some images of the light as set up for its intended purpose?

But it's hard to see, Alexey feeds light directly into monochromator, I use a fiber, everything is pretty standard.
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Alexey.Danilchenko

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> How about adding some images of the light as set up for its intended purpose?

But it's hard to see, Alexey feeds light directly into monochromator, I use a fiber, everything is pretty standard.

To add to to Iliah's comment, my monochromator came without entry slit but with entry attachment for optical cable. I use one of the Luxtron/Lumasense/Xinix monochromators found on eBay in large quantities - in those industrial Luxtron boxes (if disassembled) are usually packaged Mini Chrom compact series monochromators for visible range (considering the target usage of Luxtron devices) but with entry slits fed from remote sensing chamber via optical cable. To make it more compact and avoid any light losses I always attempted to feed the light directly into monochromator (initial version with tungsten halogen light was using optical cable with collimating lens at the end - I posted pictures of that setup here in dcamprof thread). After lots of experimentation with achieving good focused light on the monochromator output in the integrating sphere, I made up my own entry - essentially optical cable entry that came with it fused with single element collimating lens of the small focal distance. The position was chosen such that it focuses the light falling on the lens into integrating sphere producing quite clear projection of output slit (I think it's the best so far that I could do with DIY approach without any special tools).

From there on the rest is simple - light source directed pretty much on entrance (the collimating lens) and quite close to it. The diameter of this lens is about 4mm and it is fused into plastic entrance block by Sugru and sealed, no photo will show it clearly enough unfortunately (tried that before).
« Last Edit: July 04, 2018, 03:42:33 PM by Alexey.Danilchenko »
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WayneLarmon

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To add to to Iliah's comment, my monochromator came without entry slit but with entry attachment for optical cable. I use one of the Luxtron/Lumasense/Xinix monochromators found on eBay in large quantities

One like this?

All of this has been, um, educational.  I've got a small stack of textbooks I am working through (Hunt's Measuring Color and Reproducing Color, several "Introduction to Matlab" books (and learning enough math to do at least some of the math in the above textbooks), several Particle Photons to wake up, following Iliah's suggestions on working with SMT components, etc.

This thread has been very rich for me.  I'm just poking my head up to thank everybody for all the valuable information.  Now back to reading.
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Alexey.Danilchenko

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One like this?

Yes. Inside this one is one of these https://www.dynasil.com/product-category/mini-chrom-monochromators/digital-mini-chrom-monochromator/ together with photomultiplier and supporting circuitry. Those industrial second hand blocks are great way of getting monochromator for a fraction of its original price.

My one comes from Luxtron/Lumasense 1108
« Last Edit: July 04, 2018, 03:50:48 PM by Alexey.Danilchenko »
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Jack Hogan

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Sorry not quite following the question. The light head mounted to face monochromator entry slit at a distance that keeps light in a small condensed circle. Nothing special around that especially since monochromatots do differ. I'll eventually post photos of all my setup and some details about construction but not yet.

Right.  Share a picture so we can see what you are doing and how you are doing it :)

Great stuff Alexey and Iliah!

Jack
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Alexey.Danilchenko

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Right.  Share a picture so we can see what you are doing and how you are doing it :)

When its ready perhaps, but not yet. Monochromator is a box with input and output so all photo will show you is a light next to a box. Similar to this for example:



The generic article for Monochromator lights - this for example would perhaps be of some use.
« Last Edit: July 04, 2018, 05:07:17 PM by Alexey.Danilchenko »
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Iliah

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> avoid any light losses

Exactly. It is may sound trivial: when a monochromator is used as a tunable filter in such an application, light losses are something to avoid, because with insufficient light the sensor will be characterized for untypical integration time. A procedure for calculation is presented here: https://www.newport.com/t/calculating-monochromator-throughput Because monochromator output is partially polarized, some further losses on sensor sandwich are possible.
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