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  #91  
Old March 17th, 2008, 01:59 PM
Asher Kelman Asher Kelman is online now
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Drew,

I'm glad you have made this effort to address this matter. I'll add further to this. Michael Tapes assistant will just grab a disk and fill an order. There's absolutely no selection. This is a mature product. Add to that Michael has worked hard to build his reputation. It's not worthwhile to him to risk that! Also he's honest. Add to that that he sells so many of his WhiBal cards and is so fully involved with his other work that no one is going to stop, find a "better" card or a card that will make another product look bad!

Now that this subject has been raised, no doubt we'll see a resurgence of independant testing for specific uses. Debate like this is so helpful in educating each other on what great new reference tools are available for getting the color right.

It's the reflective and transmissive properties of the devices that need to be related to real world needs. Do you want picture taken in different places to match the scene or what the brain gets out of that by removing other hues from odd light sources.

So promoting is one job but underpinning claims with data will make a product not only popular but also trusted for neutrality. For me, the more these helpful devices are examined and do well, the better.

All this is good.

Asher
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  #92  
Old March 17th, 2008, 02:24 PM
Doug Kerr Doug Kerr is offline
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Hi, Drew,

Quote:
Originally Posted by Drew Strickland View Post

Even though Doug has no way of knowing this, I made sure I had no idea which unit he was to receive.
I would never have thought otherwise, at least until you raised the spectre that others had (improperly) done otherwise.

Quote:
When consumer reports [sic] tests their new car models and reports their gas mileage, they don't take the numbers on the window at face value. They drive the car and measure what they actually get using their own independent "instruments."
And I assume, after having bought precisely-calibrated glass vessels from Van Waters and Rogers to measure the gasoline, they send them out a lab to have the markings validated.

Best regards,

Doug
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  #93  
Old March 18th, 2008, 06:43 AM
Doug Kerr Doug Kerr is offline
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Default for Bart re L*a*b*

Hi, Bart,

This is in regard to my assertion (which you pointed out to be erroneous) that in L*a*b* space, for a constant chromaticity, these ratios are constant:

a*/L*

and

b*/L*

As I later found out, the ratios that are constant for a constant chromaticity are:

a*/(L+16)

and

b*/(L+16).

I went on to say that I thought for sure I had seen some reference that led to my original assertion, but I couldn't put my hands on it. Well, it showed up. It relates to the L*u*v* color space!

There, in fact, for a constant chromaticity, these ratios are constant:

u*/L*

and

v*/L*

With respect to the du'v' plane I have been using lately, it turns out that, for an L of about 75, then one unit of u* or v* corresponds almost directly to 0.001 unit of du' or dv', respectively.

And, in the L*C*H(uv) model, for an L of about 75, one unit of C* corresponds almost directly to 0.001 unit of du'v'.

Isn't this fun?

Thanks again for your help in all this.

Best regards,

Doug
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  #94  
Old March 18th, 2008, 07:01 AM
Bart_van_der_Wolf Bart_van_der_Wolf is offline
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Quote:
Originally Posted by Doug_Kerr View Post
I went on to say that I thought for sure I had seen some reference that led to my original assertion, but I couldn't put my hands on it. Well, it showed up. It relates to the L*u*v* color space!
Ha, that explains where it came from!

Quote:
Thanks again for your help in all this.
And thank you for your contributions. As long as we keep checking each other's findings, everything will be fine and result in more insight for all.

Kind regards,
Bart
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  #95  
Old March 18th, 2008, 01:12 PM
Drew Strickland Drew Strickland is offline
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I have posted up another basic (very basic) example of how the center-weightedness of The Color Parrot provides an advantage in mixed lighting situations over other non-targeted white balance diffusers.
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  #96  
Old March 18th, 2008, 03:24 PM
Bart_van_der_Wolf Bart_van_der_Wolf is offline
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Quote:
Originally Posted by Drew Strickland View Post
I have posted up another basic (very basic) example of how the center-weightedness of The Color Parrot provides an advantage in mixed lighting situations over other non-targeted white balance diffusers.
Hi Drew,

You probably haven't, but I wonder what would have happened if you just had used a diffuserless shot as the CWB reference image.
I assume the result would be better yet.

The only meaningful contribution of the backlight in your setup seems to be in confusing the diffuser ...

Bart
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  #97  
Old March 18th, 2008, 04:27 PM
Doug Kerr Doug Kerr is offline
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Hi, Drew,

Quote:
Originally Posted by Drew Strickland View Post
I have posted up another basic (very basic) example . . ..
Thanks for putting up this demonstration. The pictures are nice. You went to a lot of effort to construct a nicely illustrative setting.

I assume that when you say "more targeted", you mean that the directivity pattern of the Color Parrot is "narrower" than many other diffusers. (You have never really said.) (Our v 1.0 is narrower, according to my measurements.)

You commented that to have used the "incident method" one would have to have aimed the diffuser at the "dominant light source", and point out that there would be some question about what that would be in this situation.

"Pointing the diffuser at the dominant light source" is a widely-held misconception regarding incident light measurement. If there is any single rule for the use of an acceptance diffuser at the subject that makes theoretical (sorry) sense, it is to have the diffuser parallel to the subject surface that is to be photographed. (Of course there isn't always a clear meaning to that, either, which is why in extreme mixed light situations with a "non-flat" subject there is no single "ideal" color balance.)

The relatively-narrow directivity pattern of the Color Parrot means that for it, the description of the "at the camera" measurement technique as "reflected light", rather a misnomer for most diffusers (in my opinion), comes more nearly into its own. And aren't we glad that our subject here has an apparently very neutral reflective color!

Measuring the chromaticity of the light reflected from it, as a basis for white balance correction, should in fact make it "whiter" in the corrected image. Unfortunately, we could expect it would do somewhat the same thing for a pale yellow shirt, or a pale pink one.

At the expense of playing an old tune here, I just cannot understand the notion that measuring the chromaticity of the light reflected from a subject would be desirable for reference for white balance correction (except for subjects handily wearing chromatically neutral clothing), and that doing that in a "more so" way (through a narrower directivity pattern) would be even better. But of course I'm hampered by all this silly color science stuff that I picked up someplace.

In any case, I'm still waiting for somebody to give me a story (maybe not even true, or even believable - just a whole story) about how real "reflected light measurement" could work.

Thanks again, Drew, for your explanations.

Best regards,

Doug
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  #98  
Old March 18th, 2008, 04:29 PM
Doug Kerr Doug Kerr is offline
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Hi, Bart,

Quote:
Originally Posted by Bart_van_der_Wolf View Post
Hi Drew,

You probably haven't, but I wonder what would have happened if you just had used a diffuserless shot as the CWB reference image.
I assume the result would be better yet.
With a subject cloaked in white, I would think so.

Best regards,

Doug
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  #99  
Old March 18th, 2008, 07:23 PM
Doug Kerr Doug Kerr is offline
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Bart makes a really good point. If our interest (for whatever reason, and you all know I don't believe in that at all) is to measure the chromaticity of the light reflected from the subject, why don't we (especially with a Canon EOS camera) just aim the camera, with no diffuser, at the subject (making sure his shirt fills the central circle), shoot, and nominate that frame as the white balance reference frame.

So then why do we want to use a diffuser at all? Remind me - what is it that the diffuser does for us in this situation?

So either we believe that it is beneficial to capture for measurement, specifically, the light reflected from the subject, or we don't. Which is it?

Bart, I think that is the greatest invention since wooden shoes. Bravo!

Best regards,

Doug
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  #100  
Old March 18th, 2008, 07:30 PM
Asher Kelman Asher Kelman is online now
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Doug,

I must say that when I started to use the WhiBal I said to myself, why bother as I almost always could find something that worked pretty well and then I did the rest by eye.

White collar, white table cloth, white teeth, whites of eyes, black of eyes, black suit, silver fork but not highlight, concrete floor or pillar, stainless steel watch are common items I use.

However, with the WhiBal, I came closer to what I wanted much faster.

The key is that one may not actually want the shot to be as observed but somewhat warmer or cooler. So ultimately one needs judgement.

Today, I always try to take a reference shot. If not, I can still manage pretty well.

When the Color Parrot arrives, I'll see how it flies!

Asher
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  #101  
Old March 18th, 2008, 07:40 PM
Doug Kerr Doug Kerr is offline
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Hi, Asher,

Quote:
Originally Posted by Asher Kelman View Post
When the Color Parrot arrives, I'll see how it flies!
I think you'll like it. Its shape is in many cases handier than a WhiBal Card - perhaps more easily held by the subject and "cooler" in appearance (might be thought to be a magic glass of some sort).

Drew's tests suggest that it has a very good reflective neutrality - perhaps not as near neutral as the WhiBal, but evidently closer to neutral than in its transmissive mode (when it is used as a diffuser).

Best regards,

Doug
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  #102  
Old March 18th, 2008, 10:34 PM
Drew Strickland Drew Strickland is offline
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I've posted up another example for your enjoyment.
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  #103  
Old March 18th, 2008, 10:37 PM
Drew Strickland Drew Strickland is offline
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Quote:
The only meaningful contribution of the backlight in your setup seems to be in confusing the diffuser ...
Exactly.

That's what backlights usually do to camera meters as well. These types of situations are found very regularly in event photography. The Color Parrot deals with this situation better. Far from perfect, but better in many instances.
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  #104  
Old March 18th, 2008, 10:41 PM
Drew Strickland Drew Strickland is offline
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Quote:
I assume that when you say "more targeted", you mean that the directivity pattern of the Color Parrot is "narrower" than many other diffusers. (You have never really said.) (Our v 1.0 is narrower, according to my measurements.)
Yes, in addition to the smaller effects that can be achieved by zooming in or out on the subject(s) so the target covers more or less of the viewable space in front of the photographer.
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  #105  
Old March 18th, 2008, 11:02 PM
Drew Strickland Drew Strickland is offline
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Quote:
Bart makes a really good point. If our interest (for whatever reason, and you all know I don't believe in that at all) is to measure the chromaticity of the light reflected from the subject, why don't we (especially with a Canon EOS camera) just aim the camera, with no diffuser, at the subject (making sure his shirt fills the central circle), shoot, and nominate that frame as the white balance reference frame.

So then why do we want to use a diffuser at all? Remind me - what is it that the diffuser does for us in this situation?

So either we believe that it is beneficial to capture for measurement, specifically, the light reflected from the subject, or we don't. Which is it?
What's with the extreme black and white choices here?

You answered your own question here, Doug. The diffuser, diffuses. Both diffusers, diffuse. The Color Parrot diffuses a smaller field of view (center-weighted/ targeted/ selective/ directivity pattern) whatever you wish to call it.

In the first posted example, just pointing it at the neutral white coccoon probably would work pretty well. But, this is just coincidence. A white coccoon just happened to be used in this example becuase it is obvious to those of us viewing the image what white should look like. The second set of images were taken by "metering" the face and making that the reference frame. The face is not a neutral white, (sorry if you're reading this honey.) You're not really white, afterall.

Anyhoo, we need a diffuser to diffuse the different light being reflected and mix it up.

Yes, light is reflected Doug. If light didn't reflect we wouldn't see much on this planet. I think what you have been trying to say all along is more along the lines of this.

The direct light hitting the diffusion device often overpowers the reflected light of any single surface in the field of view. I'm sure you have a much more concise way of stating this. I'll leave that to you and Bart. This is true, but there are many limitations to that view, as shown by the most recent examples I have posted.

The ability to limit the light that gets diffused is often beneficial when having/ choosing to shoot using the "reflective" method. If we always shoot using the method you propose, or the so called "incident" method then both tools would be more or less equal in result, minus the improved spectral neutrality of the Color Parrot product. Yes, I know you have a difference of opinion on that as well. That's ok. Life wouldn't be any fun if there were no variety of opinion. What is that quote, something about iron sharpening iron?

Actually, come to think of it. If I used your method of standing where the subject is and I have to choose a dominant light source from two or three different temperature light sources then having a more targeted angle of coverage would also be beneficial, as I would be taking in less of the other two "extraneous" light sources. I'll have to look into that.
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  #106  
Old March 19th, 2008, 07:06 AM
Doug Kerr Doug Kerr is offline
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Hi, Drew,

Quote:
Originally Posted by Drew Strickland View Post
Yes, in addition to the smaller effects that can be achieved by zooming in or out on the subject(s) so the target covers more or less of the viewable space in front of the photographer.
I'm not sure I follow yet. Are you referring to "zooming" the lens on which the diffuser is mounted? By "cover[ing] more or less of the viewable space in front of the photographer", do you mean that the angle subtended by your "target" (as measured from, say, the focal plane) varies as the lens extends during zoom (if it does)? Or do you mean that if the "target" were imaged on the focal plane by the lens, that it would cover a different part of the focal plane as the lens is "zoomed"? I just don't get the picture of what you are saying.

Best regards,

Doug
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  #107  
Old March 19th, 2008, 07:33 AM
Doug Kerr Doug Kerr is offline
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Hi, Drew,

Quote:
Originally Posted by Drew Strickland View Post
What's with the extreme black and white choices here?

You answered your own question here, Doug. The diffuser, diffuses.
Sorry that didn't occur to me.

Quote:
The ability to limit the light that gets diffused is often beneficial when having/ choosing to shoot using the "reflective" method. If we always shoot using the method you propose, or the so called "incident" method then both tools would be more or less equal in result, minus the improved spectral neutrality of the Color Parrot product. Yes, I know you have a difference of opinion on that as well.
Her is the problem I have with the "reflected light" method. I have heard no story (form anybody) about how what is presented to the camera in that technique should be indicative (in the general case) of what we would like to know (and can't perhaps conveniently measure): the chromaticity of the illumination on the subject.

We can stand at the camera and, by using diffusers with different directivity patterns, collect light arriving at the camera location from various sources (some reflected from the subject, some direct from sources that emit some toward the camera, and so forth), "mix them together" based on the behavior of the diffuser, and have the camera measure the chromaticity of the mélange.

You seem to make the point, especially in the discussion of your new example, that it is not desirable to pick up (so much of) the (orangish) light from the backlight (which emits substantially in the direction of the camera). I certainly agree. We are not intersted in measuring the chromaticity of the light from the backlight. For one thing, in your one camera location, it has little effect on the color of the face of the "subject". (Maybe some,. since I suspect that "square Bob" has a partly-translucent head, but that's another matter.)

And I would assume that, similarly, you would not want the diffuser to pick up (too much of) the light emitter toward the camera from the (bluish) key light (but that's not so much of an issue here, since it doesn't look as if it emits much toward the camera.

So what amount of the light emitted from those two sources would it be desirable to pick up?

Is this a fair description of what you say we want the diffuser to do for us: "Pick up a fair amount of the light coming toward us from the subject, and some (but not too much of) the light coming to us from other directions" ?

And the hope is that, by so doing, we will present to the camera a good approximation of the light that illuminates the face of the subject we are trying to photograph?

Or isn't the latter really our objective? Maybe my error is in believing that.

In any case, I just can't make the connection between what you seem to say the diffuser should "pick up" and what the camera needs to know to do a reasonable job of white balance.

And again, I have never heard even the supposed answer described.

Best regards,

Doug
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  #108  
Old March 19th, 2008, 10:12 AM
Doug Kerr Doug Kerr is offline
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Default Those pesky cosines

Hi, Drew,

Quote:
Originally Posted by Drew Strickland View Post

Actually, come to think of it. If I used your method of standing where the subject is and I have to choose a dominant light source from two or three different temperature light sources then having a more targeted angle of coverage would also be beneficial, as I would be taking in less of the other two "extraneous" light sources. I'll have to look into that.
I hate to keep singing this tune (you know, we Episcopalians always sing all the verses), but the concept of, in "incident light" measurement of incident light (!), aiming the instrument at the "principal light source" is just plain wrong. It is a notion that emerges from failure to realize that the "correct" solution is just as easily available. It is a wrong as doing one's bookkeeping only including the revenue from the largest customer.

Let's review this, starting from basic principles. I know that you understand all the principles involved, but I just want to make sure you know where I'm coming from.

Our real mission here comes from the fact that, if the subject is not illuminated by light having the chromaticity of the reference white of our color space, the rendition of the subject in a delivered image will not be perceived as having "the right color".

To overcome this, we (a) can determine the chromaticity of the light that actually illuminates the subject, (b) determine how this differs from the chromaticity of the pertinent reference white, and (c)use that difference to direct a "color transform" that results in the image of the subject, when viewed as a delivered image, having the "appropriate" appearance.

Let's imagine that we wish to "determine the chromaticity of the light that illuminates the subject" by measurement. We can do this (as is done in much professional work) with an incident light colorimeter. But we don;t all have those.

But we can also do it by fitting our camera with an "acceptance adapter" (a "white balance diffuser)" that allows the camera to be used to make the measurement. That way, for one thing, then result is already where it needs to be (inside the camera!). Otherwise, we would have to enter the meter reading into the camera, and guess what: it doesn't have a way to enter it!

Now I will start wioth an "idealized" case to allow the principles to be best visualized.

Suppose have a subject whose surface of interest is flat (and oriented in some arbitrary direction) and all the incident light comes from a single source. We put our "instrument" (camera with diffuser in place) at the subject location, facing in some arbitrary direction (presumably something like toward the camera position for the shot). The diffuser collects light from the single source, "homogenizes" it, and passes "a sample of the mix" through the lens to the camera sensor for determination of its chromaticity. That's easy.

Now, let's raise the ante., We still have our flat subject, but now the illumination comes (only) from two sources, a reddish one from in front, stage right, and a bluish one from in front, stage left.

The illuminance on the subject (thats a specific photometric quantity, not just the concept of "illumination") from each of these sources is proportional to the luminous flux density of the beam at its "destination" and to the cosine of its angle of incidence. (This is a result of the surface being "Lambertian", which we must assume for the moment.) Suppose that all the factors involved mean that the illuminance provided by both sources is the same.

Then, the chromaticity of the "illumination" (which is what affects the color of the light reflected from the subject and captured by the camera in the actual image) can be thought of as the "average" of the chromaticities of the two light "beams".

How is the camera going to know what that is? Well, suppose that the way the diffuser "combines" the light striking its surface from different directions of incidence (different illumination "beams") is such that contribution of each to the "mélange" delivered to the camera sensor is weighted by the cosine of the angle of incidence of that "beam". (I have a couple of diffusers that do very nearly that.)

Then, we orient the face of the diffuser the same way the subject's (flat) surface is oriented. Thus, for any "beam" of light, the cosine of its angle of incidence on the subject will be the same as the cosine of its angle of incidence on the diffuser.

In other words, that kind of diffuser makes the camera respond to the different light sources exactly the same way that the subject surface does.

Thus, the chromaticity determined by the camera (by measuring what has been collected by the diffuser) is precisely the one that it needs to know.

Note that this involved no notion of "facing the diffuser toward the principal light source."

Now suppose that, in a specific version of this case, one of the two light sources "twice as potent" as the other (with respect to the illuminance it creates on our subject. Suppose we then said, "Great! Now I can easily tell which one is the 'principal' light source and aim my diffuser toward it - I read someplace that is what I should do.", and we did that.

Now, the light from the so-called "principal" light source is weighted, in the combination being collected by the difuser for presentation to the camera, by the factor 1 (the cosine of 0°), while the other by a smaller factor (the cosine its angle of incidence on our diffuser, a larger angle than its angle of incidence on the subject, since we have the diffuser "aimed" at the other light source.)

The result will be that, even though this light source contributes 1/3 of the total illumination on the subject, and its chromaticity will actually be weighted by a factor of 2 greater than that of the other source in affecting the observed color of surface, we will weight it much more heavily in our measurement. Thus, the determination of the incident liught chromaticity will not represent the illumination on the subject, and the color correction will be "wrong".

(If the "principal" source were the red one, then our determination of the incident light chromaticity this way would be "too red", and the corrected image would be "too blue".)

And this is why (at least under this "ideal" model, "aiming at the principal light source" is just the wrong procedure.

Now lets leave the blackboard and go into the studio. Suppose that one or more of our premises here were not so. suppose the subject surface were not flat; suppose its behavior were not Lambertian. Then what?

Then my model of "ideal chromaticity determination" doesn't exactly work. Would aiming the diffuser "at the principal light source", however, work "most nearly correctly"? No reason to believe that. It might. It might be best to aim the diffuser toward the camera trailer, or the model's agent. We have absolutely no way to generalize.

And of course, of we have the "serious" mixed light mess I described, and the subject were a human face, there would be no color correction that would produce a "natural" rendering of the whole face. If we made our measurement with the diffuser facing the same way as the model's nose (and lets suppose that were toward the camera), then the right side of the models face would look decidedly reddish, and the left side decidedly bluish.

Now suppose that the red light source was known to be the more potent. The, if we had made the measurement with the diffuser "facing the camera", we would end up with the center of the model's face still being corrected "properly" (ah, the power of those little cosines - they work for us even if we don't understand them!), the right side a bit reddish, the the left side a little bluish. (And the right side would have been "brighter" than the left side.)

Now suppose we decided to hark to the "common rule" and aimed the diffuser at the red light.

Now, in the corrected image, the model's right side would have been about "properly balanced", the center of the face would have looked a bit bluish, and the left side a lot bluish.

Is that the result we want? (Elvira's agent says, "Great - just what she wanted!") And if so, then the "rule" worked fine. Good for us. But it might not be what Red Fox, the famed Cherokee author, would prefer.


In any case, the argument of the practical weakness of "incident light" measurement of the incident light is that it might be hard to figure out which is the "principal" light source doesn't hold, since that is not a matter of actual importance.

This is not to say that "incident light" measurement is always doable, or handy, nor to say that there is no useful alternative. That's another story altogether. It's just that when we are speaking of something, for better or worse, I like to speak of it in a way that matches the reality.

The notion of "facing the principal light source" is just a misconception. It doesn't match the "ideal case", and is not predictably the best in various "realistic cases".

Best regards,

Doug
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  #109  
Old March 19th, 2008, 11:02 AM
Doug Kerr Doug Kerr is offline
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Default Those pesky cosines - 2

I just realized I had given a really long discussion of "why we shouldn't think in terms of aiming the diffuser at the 'principal' light source".

Here's a shorter one:

Q. We want the diffuser to emphasize the light source that has the greatest impact on the illumination of the subject. So shouldn't we point the diffuser at that source?

A. No. If we put hold the diffuser parallel to the subject surface, it will automatically give each source just the weight it deserves.*

* That is, if it has about a "cosine" directivity pattern. Otherwise, all bets are somewhat off.

Best regards,

Doug
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  #110  
Old March 19th, 2008, 02:00 PM
Asher Kelman Asher Kelman is online now
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Drew,

If anyone sets up colored lights then I assume they want added color. There's no point in adding color in a studio when one can just as easily use strobes with matched temp!

One has to be able to paint if one uses paints! In that case one needs to do color balance before the gel is added!

Asher
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  #111  
Old March 19th, 2008, 02:41 PM
Doug Kerr Doug Kerr is offline
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Hi, Asher,

Quote:
Originally Posted by Asher Kelman View Post
Drew,

If anyone sets up colored lights then I assume they want added color. There's no point in adding color in a studio when one can just as easily use strobes with matched temp!
I'm sure that was an intentionally-unrealistic situation just to force insight into how the Color Parrot would respond (perhaps a bit like Adenosine in a stress test).

I'm not sure I understand the result, though.

Best regards,

Doug
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  #112  
Old March 19th, 2008, 07:40 PM
Doug Kerr Doug Kerr is offline
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Default Sure a cute model

Hi, Drew,

Well, we both are sure lucky to have some cute models available for demo shots.

Your latest shots in your "Center Weightedness" series are interesting.

It is in fact interesting that the Color Parrot made such a different determination of the incident chromaticity than the un-identified "non targeted diffuser". It certainly shows that the narrower directivity gives a "better" result in this "measure from the camera" exercise.

What the actual numbers tell me, though, is that the Color Parrot (even the "extra-targeted" 1.1) is still picking up a lot of the orange from the backlight (as we would well expect). It read the light at 3700K. But with the front of the model illuminated wholly with "daylight" fluorescents, we would expect to get a reading of perhaps 5500K, perhaps even bluer for the light reflected from the model's mostly-blue garb (which is the light you seem to want to measure for some reason).

What would you have done to actually get a good color balance?

Even in the second image, the model's skin looks pretty blue - of course I don't know her, so maybe that's accurate.

And I hate to talk about a lady's garments (other than, of course, as required in a forensic inquiry), but one might expect her shirt to have been sort-of-white, and in the image you posted, it seems to have come out about L*a*b 84.9, -5.4, -18.2. But perhaps the shirt is color-coordinated with her jacket and scarf.

And she sure seems to have "over-brightened" her pretty teeth.

Now if you could give the Color Parrot a really narrow pattern, so it only picked up the subject, then she would have had a lovely rosy glow (but yellowish teeth).

Now maybe something in between would be just right.

Best regards,

Doug
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  #113  
Old March 20th, 2008, 11:06 PM
Drew Strickland Drew Strickland is offline
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Quote:
Originally Posted by Asher Kelman
If anyone sets up colored lights then I assume they want added color. There's no point in adding color in a studio when one can just as easily use strobes with matched temp!

Doug replied:
I'm sure that was an intentionally-unrealistic situation just to force insight into how the Color Parrot would respond (perhaps a bit like Adenosine in a stress test).
That's correct. The different colored lights were used to more easily illustrate a potential real world example of light sources of different temperatures.
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  #114  
Old March 20th, 2008, 11:15 PM
Drew Strickland Drew Strickland is offline
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Quote:
It is in fact interesting that the Color Parrot made such a different determination of the incident chromaticity than the un-identified "non targeted diffuser". It certainly shows that the narrower directivity gives a "better" result in this "measure from the camera" exercise.

What the actual numbers tell me, though, is that the Color Parrot (even the "extra-targeted" 1.1) is still picking up a lot of the orange from the backlight (as we would well expect). It read the light at 3700K. But with the front of the model illuminated wholly with "daylight" fluorescents, we would expect to get a reading of perhaps 5500K, perhaps even bluer for the light reflected from the model's mostly-blue garb (which is the light you seem to want to measure for some reason).
Yes, that's correct. It did pick up some of the backlight. It is "center-weighted", not a spot meter. In this case a "spot metered" version might have been preferable. But often, center weighting is a nice all around metering algorithm. But alas, this is a hardware device and cannot so easily be changed in function. I attempted to manufacture a spot metered version early on, but ran into some issues. Although, the concept worked and was sound.

I think there may now be a way to manufacture a "spot-metered" targeted version. You'll probably guess how when you see your new v1.1 models that were packaged up tonight.

Although, a spot metered version is less than the overall ideal for most generic shooting situations, it would have its uses. It would need to be sold for the specific lens size it would be used with. This gets rid of the one size fits all advantage. But, it may well be a deserving product. The target on 1.1 is about as narrow as I think we can get without running into issues with specific zoom lengths and other lens/ body characteristics.
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  #115  
Old March 20th, 2008, 11:21 PM
Drew Strickland Drew Strickland is offline
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Quote:
Q. We want the diffuser to emphasize the light source that has the greatest impact on the illumination of the subject. So shouldn't we point the diffuser at that source?

A. No. If we put hold the diffuser parallel to the subject surface, it will automatically give each source just the weight it deserves.*
This is getting closer to something I could actually use in very "simple" directions with the product. But, we have to get rid of the word parallel. Yes, I know it is very concise. But the average photographer will be turned off with this language.

I revised the instructions for 1.1. Please do let me know what you think.
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  #116  
Old March 21st, 2008, 01:21 AM
Doug Kerr Doug Kerr is offline
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Hi, Drew,

You recently quoted me as follows:

Quote:
Q. We want the diffuser to emphasize the light source that has the greatest impact on the illumination of the subject. So shouldn't we point the diffuser at that source?

A. No. If we put hold the diffuser parallel to the subject surface, it will automatically give each source just the weight it deserves.*
You inadvertently omitted the note that goes with my answer. The compete answer is stated here:

Quote:
A. No. If we put hold the diffuser parallel to the subject surface, it will automatically give each source just the weight it deserves.*

* That is, if it has about a "cosine" directivity pattern. Otherwise, all bets are somewhat off.
The Color Parrot, of course (apparently by design) substantially departs from a cosine pattern (apparently, from the recent discussions, even more so in the case of the new v 1.1 than for the original v 1.0).

Best regards,

Doug
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