DSLR testing sites like DXOmark and Imaging Resource use HMI and LEDs for color

[Alexey.Danilchenko]

There is no (as in zero) chance of thermal runaway if you're using the modules and you stick to wiring them in parallel. That's what the resistors built into them are for. If you want to work with the LEDs directly, then, as mentioned above, you need specialist knowledge and equipment.

Small correction - the strips are wired to each other sequentially, this way the actual LEDs end up wired in parallel strings (7 LEDs in each string)

[WayneLarmon]

I'm not knocking your instrument's accuracy. I have the same question you do about what the numbers mean to what I'm suppose to see. To cut to the chase do you see the Crees color of white (greenish to orangish yellow) to be the same as I've posted in my images?

If your Crees are showing you perfectly neutral colorless white light viewing a spectrally flat gray target then either your eyes or my eyes are playing tricks on us or the Crees have quality control issues in maintaining consistency bulb to bulb in rendering neutral white light or the measuring instruments are not that sensitive.

I have two Hyperikon LED floods that are rated at 5000K. One has the greenish yellow tint and the other a more neutral blueviolet tint which my camera's AWB shows an ACR tint slider in the minus (greenish) region meaning it sees the magenta pink portion of violet. The camera is seeing what my eyes are seeing. My eyes know when it is seeing something that looks neutral and when it is not.

What and how does a measuring instrument define neutrality if they're going to assess the same same number to two different tints of white lights?

I'm not really sure.  I just did my own visual test.  I set up a small test arrangement of several objects which include a French's mustard container, a ColorChecker chart, and a WhiBal card.  The other objects were chosen to be commonly available (at least in the US) to get red, (sort of) green, and blue into the scene.  (Maybe we need a scavenger hunt to find the best commonly available color test obects (that aren't a ColorChecker card).  Go to Walmart with an empty shopping cart and get...)

I don't see a greenish tint because I white balance on a WhiBal card as the first step in ACR.  I have no doubt that the hardware store lights have a consistency issue.  There is only so much that can be done in the power supply of a bulb that sells for less than $10.  This is why Alexey is paying so much attention to the power supply with his Yuji lights.

You mentioned cadmium yellow.  I don't paint and don't have the foggiest idea of what pigments were used in the paintings I'm shooting.

I shot raw and white balanced on the lower right portion of the WhiBal card. (This is the way I always shoot paintings.)   I adjusted exposure (in ACR) so that this portion of the card was approx. 186.  They are

1. Walmart 75w daylight LED
2. Cree 100w daylight LED
3. Aputure Amaran AL-H198 LED panel
4. Outside under a cloudy sky, about 1:00 PM EDT.  ColorMeter measured the CCT as being about 6000K

I'm attaching the four images.  The three done under artificial light look pretty similar.  The one done outside looks different, 1., because the CCT is higher (shows on the background) and 2., because the angle of the light is different.  (And 3, because the one done outdoors is slightly out of focus because I quickly shot handheld because I felt like a doofus crouching down in my driveway shooting a small white thing balanced on a storage tub.)

When I expand the images so the ColorChecker chart fills the field of view I can't see much difference between any of them.

What accuracy measurement number does one apply to tell us which bulb is the most accurate to daylight?

This is what I want to know.  As I showed in my earlier post, the Walmart, Cree, and Aputure LEDs have different measurements.  The TLCI (which is how cameras render color) are close to 97 for both the Cree and Aputure lamps.  This should mean something.

[Tim Lookingbill]

Thanks for posting the images, Wayne. I'm glad I chose the French's Mustard bottle as a target because toggling through all four shows the gradual increase of green with Walmart being the worst, then progressing toward less green to the intended slightly reddish yellow that is Cadmium Yellow in the 6000K shot.

The CCchart yellow patch which is too small to detect color change bares me out with the standard known yellow Lab numbers of L*80,a*4,b*80 which is spot on with 6000K but the Caucasian skin patch has a pink bias of L*70,a*18,b*15 which indicates that overcast clouds have a slight green bias which is why I shot my outdoor target under direct sunlight.

I'ld say the Aputure is the most accurate with spot on Lab numbers for Caucasian skin and yellow patch (just off by 2 points in the (a*) channel for yellow which is undetectable). Lab numbers can be off by as much as 5 points in either channel without a visual difference which is why I chose the mustard bottle target which does show differences even though the yellow patch Lab numbers are so close between all four. Walmart's bulb is in the minus region in the a* channel. That indicates quite a bit of green.

So visually you don't see a greenish yellow hue in the white light of the Crees or Walmart bulbs when you first turn them on?

[Tim Lookingbill]

To clear up something about my questioning the accuracy of your measuring instruments and software I was under the impression you were measuring the lights as they are with their greenish yellow white hue but I don't know what surface you pointed the Colormunki spectro to arrive at the numbers.

Your measurements are based on reflected light off something but you didn't make it clear what it was. What doesn't make sense and might be cleared up at least for me regarding the greenish yellow tint of white I see from the Cree and Walmart bulbs is maybe you were measuring off a surface these lights were lighting that has optical brighteners.

What were you measuring off of to arrive at the CRI/CCT numbers you posted?

[digitaldog]

Lab numbers can be off by as much as 5 points in either channel without a visual difference which is why I chose the mustard bottle target which does show differences even though the yellow patch Lab numbers are so close between all four.

Utter rubbish! Easy to dismiss as shown below where one Lab channel differs by 5 units and we see (numerically via deltaE of 3.88 and visually) that statement is totally untrue.
Readers of Mr. Lookingbill, beware of such kinds of statements made that are colorimetrically untrue and by someone without the hardware or software to make such incorrect generalities about color! He may ignore my corrections to his text, but you can ignore the misinformation from his posts after I've corrected them colorimetrically as we see here:

[digitaldog]

What were you measuring off of to arrive at the CRI/CCT numbers you posted?

The illumination! If you owned or ever used a spectrophotometer that measured an light source, you would know this and maybe HOW to do so correctly.
You used the wrong tool (a camera) for this task and the question you asked Wayne applied to your incorrect use of a camera to “capture” not measure anything really. What software did YOU not use to get CRI values you didn’t provide?

[WayneLarmon]

To clear up something about my questioning the accuracy of your measuring instruments and software I was under the impression you were measuring the lights as they are with their greenish yellow white hue but I don't know what surface you pointed the Colormunki spectro to arrive at the numbers.

Your measurements are based on reflected light off something but you didn't make it clear what it was. What doesn't make sense and might be cleared up at least for me regarding the greenish yellow tint of white I see from the Cree and Walmart bulbs is maybe you were measuring off a surface these lights were lighting that has optical brighteners.

What were you measuring off of to arrive at the CRI/CCT numbers you posted?

I need to reread my books on color science.  It has been several years since I studied them.  Now I'm working through Color Management for Photographers, then on to more advanced ones.  Right now, I don't know how to do the L*a*b analysis you are doing.  (But I do generally understand L*a*b.)  I've been concentrating on the raw CRI, TLCI, Duv, and R9 measurements.  And on the overall shape of the spectrums.

When I turn the lights on for photographing I don't pay attention to tints I see--cameras renders color differently than eyes do.  (Especially with the Luther/Ives situation.)  This is why there is CRI for human eyes and TLCI for cameras. (I think.)  Clicking on a WhiBal card in the frame takes care of tints (I think). 

The ColorMunki Design spectrophotometer I use has two ports for reading.  The one at the top is for reading ambient light through a diffuser.  When it is set up for reading ambient light, I point it right at the light, usually six to eight inches away from the light to swamp out room reflections.  I always do several measurements from slightly different angles to ensure that reflections aren't contaminating the reading.  (Think of putting a microphone right next to a guitar speaker--any room reflections are too small to be meaningful.)

The bottom port on the ColorMunki is undiffused.  It is for either reading reflected color (say, from printer profile charts, or a paint/fabric sample).  Or for reading undiffused light (spot emission.)

The ColorMunki Design is out of production.  I think that is replaced by the i1Studio Spectrophotometer, which is a better name.  Before, XRite had ColorMunki spectrophotometers and ColorMunki colorimeters (can only be used to calibrate monitors) which confused people.

Photographers use spectrophotometer for profiling printers and for measuring light.  Unless you go used, the ColorMunki (or i1Studio) is the cheapest spectrophotometer you can get new.  If you want to profile a printer, it comes bundled with Xrite software.  Or you can use ArgyllCMS.  (If you really want to profile printers the more expensive XRite options are better.  But cost about three times as much.)

Even though spectrophotometers can be used to calibrate monitors, colorimeters are better.  I use an i1 Display Pro to calibrate my monitors.

I put the images up at 2400x1600.  If you look at the original images I attached the ColorChecker patches are larger than they are in real life so you should be able to measure them.

[digitaldog]

Right now, I don't know how to do the L*a*b analysis you are doing.  (But I do generally understand L*a*b.)

Then you're way above Tim's understanding here. He is again not using proper tools or software to comment let alone analyze Lab values or measured the color of anything like you've done with the right equipment. Just examine the silly notion that's been easily dismissed below after Tim incorrectly wrote: "Lab numbers can be off by as much as 5 points in either channel without a visual difference". Pretty clear to someone without color vision deficiencies that the two yellow Lab values provided by him have a visual difference and that's just ONE set of Lab triplets I've analyzed (correctly) in CT&A that Tim didn't/cannot. He doesn't even understand how you correctly used your Spectrophotometer to measure the illuminant!
Go back to reading about color management from others  don't get stuck into another of Tims rabbit hole of color management absurdities.

[WayneLarmon]

Ok - so rectangular flat panels. The easiest then would be to start with the panelled LEDs (the ones you have been looking at) and perhaps DC (constant voltage) power supply. That will be straightforward to connect. Then after mounting it on some backing panel in the case with diffuser, you can run them in for some time, monitoring temperature and doing periodic measurements to monitor for thermal/current related colour shifts and whether they are within your tolerance levels. If they are then you may be perfectly happy with just DC power supply. The constant current approach is not going to work with the panels (due to the ways the soldered) or strips.

In case of Yuji - their panels are MCPCB (metal core boards) so they do have better heat dissipation that normal PCB and you may not need any heatsink installed.

Those Yuji panels by my calculations contain 21 LED in each strip: 3 parallel strings of 7 LEDs in series with resistor(s) each. Incidentally the panel's single strip specification is shared on that very page (dimensions current etc).

It also gives the output in lumens.  480 lumens per strip, 4800 lumens for the package of ten strips.

Transposing, I currently use six 100w (equiv.) lights to get enough light to shoot paintings cross polarized.  A 100w bulb is about 1500 lumens.  Six bulbs is 9000 lumens.  So I would need two sets of Yuji strips at $209 for each set and four Yuji power supplies at $45 ea.   Which adds up to around six hundred dollars, before I get into fabrication.

At this point I don't think I can justify this for shooting family paintings.  I'll spend additional time shifting hues around in Photoshop to make my images look pleasing (if not accurate.)

Orchids from what I looked at.

Look at the videos again.  They aren't growing orchids.


Thanks for all your help.  Maybe in six months or a year I might want to tackle this if I build up a fresh head of steam.  But right now, I'll stick with the lights I have.

[WayneLarmon]

Go back to reading about color management from others

Your book, along with Real World Color Management, are solid introductions to the parts of color science that matter most to photographers.   Before I tackle Wyszecki and Stiles again.

Have you considered writing a second edition?  Even though almost everything in your book is relevant today, there have been advances in technology.   P3 and HDR are coming real soon (and already exist to a certain extent in recent smartphones.)  Cinema standards are driving things.  Even for those of us that aren't videographers, the technology is coming.  And is all about color science.

[Doug Gray]

Utter rubbish! Easy to dismiss as shown below where one Lab channel differs by 5 units and we see (numerically via deltaE of 3.88 and visually) that statement is totally untrue.
Readers of Mr. Lookingbill, beware of such kinds of statements made that are colorimetrically untrue and by someone without the hardware or software to make such incorrect generalities about color! He may ignore my corrections to his text, but you can ignore the misinformation from his posts after I've corrected them colorimetrically as we see here:

Andrew, your deltaE of 3.88 is a deltaE2000. Perhaps Tim is referring to deltaE1976, since he didn't specify the version and the latter is usually meant when not specified. In your example the deltaE1976 is 5. I'm pretty sure there are colors in the yellows with a deltaE1976 of 5 but have a generally more visually accurate metric, deltaE 2000, that is less than 1. Perhaps he stumbled across some of those visually close colors and was thinking that they look awfully close even though the had a large deltaE1976. And he did say "as much as."

Looking at a set of L*a*b* values one can guess pretty closely what the deltaE1976 is. If 2 of the 3 components are the same the difference of the third is the deltaE1976. Actually, if you just think of a box with the length, height, and width having lengths that are the differences between L*'s, a*s, and b*s the distance between opposite corners of the box is the deltaE1976. Fairly easy to make a rough guess if you can visualize a box.

No such way to guess for deltaE2000 w/o digging out the somewhat messy formula.

[Tim Lookingbill]

When I turn the lights on for photographing I don't pay attention to tints I see--cameras renders color differently than eyes do.  (Especially with the Luther/Ives situation.)  This is why there is CRI for human eyes and TLCI for cameras. (I think.)  Clicking on a WhiBal card in the frame takes care of tints (I think).

The ColorMunki Design spectrophotometer I use has two ports for reading.  The one at the top is for reading ambient light through a diffuser.  When it is set up for reading ambient light, I point it right at the light, usually six to eight inches away from the light to swamp out room reflections.  I always do several measurements from slightly different angles to ensure that reflections aren't contaminating the reading.  (Think of putting a microphone right next to a guitar speaker--any room reflections are too small to be meaningful.)

The bottom port on the ColorMunki is undiffused.  It is for either reading reflected color (say, from printer profile charts, or a paint/fabric sample).  Or for reading undiffused light (spot emission.)

I believe you may be using the spectro not the way it was intended for measuring ambient light which by that very word is a human perception function for measuring the surrounding light of one's display during calibration. I don't think your ambient light is you looking straight into the light bulb 8 inches from your eyes while you edit images on the display.

The Colormunki spectro's "Ambient" feature is designed to measure the surrounding light which is not as bright around the display which the software takes into account during calibration/profiling when building the display profile. What you're doing is akin to measuring the city's water pressure with your face 8 inches from the front of a fire hose set to full blast without taking the firetruck's pump into account and any errant backwash pressure and over spray. It's not practical and its accuracy is suspect even if your face and eyes are still intact. A measuring instrument won't be accurate either without accounting for all known and unknown variables.

This is all unnecessary complexity anyway that keeps you from solving the issue you described about your family paintings having some colors not reproducing accurately on your display and thus in the print and questioning the lighting being used during the photographic process. I think you solved your lighting issue especially using the Aputure LED's.

I'm just not going to trust your spectro in the way you're using it to measure off the shelf and inexpensive daylight bulb's spectral quality. As your photos show the CCT/CRI numbers don't tell me anything that's practical in color reproduction work using the photographic process.

The Lab readings I took from Photoshop's Info Palette by downloading your images of the CCchart. It's all you can go by to tell you no matter how greenish yellow a 5000K light source makes a WhiBal neutral target appear and thus photographed by the camera (CCT/CRI numbers having no absolute correlation to visual perception in this case), when the WhiBal card is clicked for R=G=B in ACR/LR, the question remains how many colors will be distorted compared to the original photographed subject.

From your posted photo of the Aputure lit CCchart I don't think you're going to have a problem or require a lot of editing.

[Tim Lookingbill]

Wayne, can't you post a photo of a cropped section of one of your family paintings showing colors you're having trouble reproducing? That would simplify a lot of this.

[Alexey.Danilchenko]

I need to reread my books on color science.  It has been several years since I studied them.  Now I'm working through Color Management for Photographers, then on to more advanced ones.  Right now, I don't know how to do the L*a*b analysis you are doing.  (But I do generally understand L*a*b.)  I've been concentrating on the raw CRI, TLCI, Duv, and R9 measurements.  And on the overall shape of the spectrums.

The ultimate book about measuring colours in general is Hunt's "Measuring Colour". It does go into details about colour spaces, measurements, comparisons and light sources and is your definitive source (this has become my most used book in the past couple of years as I keep going and re-reading bits ).

Regarding more precise light source measurements - a good idea is to do it in integrating sphere (does not have to be commercial - it's an easy enough DIY project for weekend) to get the correct figures.

[Alexey.Danilchenko]

I believe you may be using the spectro not the way it was intended for measuring ambient light which by that very word is a human perception function for measuring the surrounding light of one's display during calibration. I don't think your ambient light is you looking straight into the light bulb 8 inches from your eyes while you edit images on the display.

The Colormunki spectro's "Ambient" feature is designed to measure the surrounding light which is not as bright around the display which the software takes into account during calibration/profiling when building the display profile. What you're doing is akin to measuring the city's water pressure with your face 8 inches from the front of a fire hose set to full blast without taking the firetruck's pump into account and any errant backwash pressure and over spray.

I am sorry but that is a load of nonsense. The ambient measurements on spectrometers achieved (with the lack of integrating sphere to aid such measuremengts) by measuring through diffuser. Pointing it towards the sole light source is the correct way to measure in this case. The power of illumination has nothing much to do with it - diffuser will attenuate the illumination to start with and the spectrophotometers sensors allow varying integration times to adjust for less or more light.

[Tim Lookingbill]

The ultimate book about measuring colours in general is Hunt's "Measuring Colour". It does go into details about colour spaces, measurements, comparisons and light sources and is your definitive source (this has become my most used book in the past couple of years as I keep going and re-reading bits ).

Regarding more precise light source measurements - a good idea is to do it in integrating sphere (does not have to be commercial - it's an easy enough DIY project for weekend) to get the correct figures.

And after all that reading can you provide any real world example of the practical application from the info that solved a problem concerning color reproduction using the photographic process?

I'm into getting things done and solving problems. If all this reading still hasn't solved a problem concerning the subject of color reproduction then this is nothing but info-tainment.

I get it that people like to read technical stuff but there isn't anyone here that has a degree or is certified as a digital imaging scientist or color scientist, not even the one consultant here who amounts to being a technical writer using color science nomenclature to come across as an authority on the subject and shilling for X-rite, Epson and other photographer services and products businesses.

[Tim Lookingbill]

I am sorry but that is a load of nonsense. The ambient measurements on spectrometers achieved (with the lack of integrating sphere to aid such measuremengts) by measuring through diffuser. Pointing it towards the sole light source is the correct way to measure in this case. The power of illumination has nothing much to do with it - diffuser will attenuate the illumination to start with and the spectrophotometers sensors allow varying integration times to adjust for less or more light.

You are not a color scientist, Alexey. You're a programmer as you've pointed out.

If you're so sure about this process then provide practical application that solves the problem of color reproduction using the photographic process.

As it is you don't know diddly squat about what you are doing. Get a degree in color science and come back and report that you solved a problem with that education that actually helped people, not just informed them. Talk is cheap and you're no expert. No one here is an expert, not even me.

I'm a pragmatist. I get things done! I don't talk about getting it done!

[Alexey.Danilchenko]

As it is you don't know diddly squat about what you are doing.

Speak for yourself please because this is impression I have after reading all the crap you are posting

[digitaldog]

Speak for yourself please because this is impression I have after reading all the crap you are posting

He really has no clue about this topic and his agenda is not learning or aiding others; ignore his severe misinformed posts and maybe he will go away.

[digitaldog]

Andrew, your deltaE of 3.88 is a deltaE2000. Perhaps Tim is referring to deltaE1976, since he didn't specify the version and the latter is usually meant when not specified. I

Doug, you of all people here can't be taking this misstatement, (one of so many just in this thread), seriously are you, no matter the dE formula?

Posted by: Tim Lookingbill: Lab numbers can be off by as much as 5 points in either channel without a visual difference...

Tim hasn't the foggiest idea of what he's suggesting, please don't give his color science fiction any degree of seriousness.