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Author Topic: Best white balance tool?  (Read 15589 times)
donaldahood
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« Reply #20 on: February 18, 2011, 11:53:12 AM »
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Exactly Mr. Wolf,
(One caveat to your comment, I may have been unclear in my description, but it is not looking in the opposite direction, but the same direction as your subject).

So if you take a reading with the Eagle i, in the same plane, facing the same direction as your subject, since it is three dimensional in design, it will pick up the exact same light, from the exact same angles, in the exact same intensities.
Thank you for helping clarify much better than I could.

Bottom line, it just works.
Thanks again Smiley
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Donald
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NikoJorj
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« Reply #21 on: February 20, 2011, 01:16:36 PM »
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it is not looking in the opposite direction, but the same direction as your subject
You do mean that you turn it towards the light, then?
(Sorry if I seem a bit understanding-impaired, but english is definitely not my mother language Embarrassed )
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Nicolas from Grenoble
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donaldahood
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« Reply #22 on: February 21, 2011, 09:51:05 AM »
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Ha Ha, I understand the impaired part. I've been told I explain things as clear as mud.
Okay let's see, if you stand where your subject is,  your mainlight is to the right of your subject, and a fill light is to the left of your subject, you point the Eagle i toward the spot you will be in when you make the photograph. With the dome shape, it will pick up the main light, fill light, as well as any extraneous light coming from any other direction. If you point a device only toward the light, you don't get the readings from the other light sources. The patent pending aspects of the Eagle i, (plug Smiley one being the dome,   allow it to read all the light, not just one light direction.
Of course, if you are outside on an overcast day, just for example, the light is the same pretty much everywhere. So just take your reading from where you are, cause it's the same light on your camera as it is on the scene in front of you. The bottom line is, you want the Eagle i to be in the same light as your subject when you make your exposure and white balance reading. The direction it's pointing isn't that critical due to the shape and filter inside the dome. It's very very user friendly by design.
Thanks for the great comments
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Donald
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carloalberto
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« Reply #23 on: February 21, 2011, 11:07:37 AM »
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Since we're on the subject. My D700 has a K setting for WB. From 2500 to 10000. I cannot figure out the logic of the step intervals but they seem smoothly gradual from very cool (2500K), to very warm (10000K). This can be seen and set visually by using Live View. My question: do any of the third part WB tools (Expodisc. Eagle i etc.) or for that matter, Preset Manual, set the camera WB at a different shade than any of the values on the D700 K scale?
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donaldahood
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« Reply #24 on: February 21, 2011, 08:50:22 PM »
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That's a great question. The Kelvin temperatures you are talking about are designated to specific lighting shades, you might say, just like fahrenheit and celcius are designated to specific hot and cold temperatures. In other words, 5000 degrees kelvin is the same color light no matter what it's coming from.
The pre-set white balances in your camera are set to certain kelvin temperatures, and they are pretty close, actually closer than auto usually is. The problem is, even though the incandescent setting in your camera might be 2500 degrees kelvin from the factory, in reality an incandescent bulb could be anywhere from 2200 degrees to 2700 degrees more or less, and even that changes as the bulb gets hotter or older. The factory presets are an average for the settings they represent.
What a custom white balance does is set the camera white balance to the exact lighting that's present. This is why an accurately calibrated white balance tool is so important. Most gray cards, especially the cheapos, are actually made to meter from, as the color of them is not consistently 18% true gray, so they will skew a white balance setting, even though they can help you set a proper exposure. It takes time to develop and consistently manufacture a properly calibrated white balance tool, but the results will be right on and the cost of a good tool is quickly made up for in the time you save in post processing. You can't add any time to your day, or your life, so why spend the fixed amount you have fixing what should have been right straight from the camera?
I hope this helps a little. Again, excellent question.
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Donald
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BartvanderWolf
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« Reply #25 on: February 22, 2011, 09:35:01 AM »
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Since we're on the subject. My D700 has a K setting for WB. From 2500 to 10000. I cannot figure out the logic of the step intervals but they seem smoothly gradual from very cool (2500K), to very warm (10000K). This can be seen and set visually by using Live View.

Hi Carlo,

Those are the settings to simulate an incandescent light source as the main lightsource with different temperatures (expressed in degrees Kelvin). Lower temperarure lightsources emit mostly longer wavelengths (IR and Red), and very little Green, and even less Blue. So a 'Reddish' lightsource will be compensated for by a 'cooler' rendering.  As the incandescent lightsource temperature goes up, the proportion of Blue lightwaves in the mix will increase, and the camera will compensate with a 'warmer' rendering. BTW, note that what we casually call cooler and warmer light, is in fact the opposite of what actually happens when measured in physical temperatures, hence some confusion.

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My question: do any of the third part WB tools (Expodisc. Eagle i etc.) or for that matter, Preset Manual, set the camera WB at a different shade than any of the values on the D700 K scale?

No, not really. The spectral composition of an incandescent light source of a given temperature is pretty well defined with the concept of Black Body radiation. What these light integrating devices do is take a weighted sample of all light colors covered by the acceptance angle of the device, and that includes all sorts of reflected ambient light (not just from the main source of light, but also floors/grass, walls, and ceilings/sky, with or without optical brighteners in clothing or paint). The camera's Raw converter however calculates it's color conversions based on the Kelvin temperatures (or the mixed spectrum approximation of fluorescent lights). So there can only be an approximation of the correct lightsource color temperature from such integrating devices at best, although one can get lucky. The analysis is complicated by the fact that a digital camera only compares the spectral composition of light in 3 broad (partially overlapping) spectral bands, which is not all that accurate for characterizing the lightsource spectrum.

The only thing that guarantees neutral White Balance under these less than ideal circumstances is a measurement at the subjects position, in the direction of the camera. The simplest way to achieve that is with a tool like a good grey card, e.g. the WhiBal. It allows to get perfect results when postprocessing  Raw files. A larger size grey card can also be used to automatically set the Custom White Balance in many cameras, which has the benefit of improved color rendering of the thumbnails of Raws, and in camera JPEGs.

Cheers,
Bart
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ejmartin
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« Reply #26 on: February 22, 2011, 10:18:46 AM »
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Because of the linear encoding of raw data (half of all the data is in the first stop on the highlight end).

I'm puzzled; why do you think this is relevant in this context?
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« Reply #27 on: February 22, 2011, 10:35:04 AM »
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Thanks to Mr. Wolf,
Note the comment, "only can be accurate at the subject position, aiming back toward the camera". This is how the Eagle i and Expodisc both work. His observation is spot on, as is the science lesson for the day. Smiley  Also, to EJMartin, I agree. somehow we are off chasing rabbits now.
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Donald
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bjanes
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« Reply #28 on: February 23, 2011, 08:19:34 AM »
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Because of the linear encoding of raw data (half of all the data is in the first stop on the highlight end).

I'm puzzled; why do you think this is relevant in this context?

This has to do with the Digitaldog's theory on exposing to the right that half of the possible levels are in the brightest f/stop of a digital exposure. Of course, all of those levels can not be resolved because of shot noise, but nonetheless one will obtain a better signal:noise with a higher exposure. If one includes the white balance card in the scene and exposes to the right at base ISO with a camera having a full well of 40,000 e- the S:N would be 190:1 with a card reflecting 90% and 85:1 with an 18% card (taking only shot noise into account). Of course, one would not use a single pixel for a WB reading but more likely the average of hundreds of pixels.  If one is using high ISO, the S:N would be much lower.

Another way to determine WB is to expose a neutral card that fills the frame to determine a peset WB. If one exposes according to the light meter, the sensor saturation will be in the range of 12-18% regardless of the reflectance of the card, depending on the calibration of the system. My Nikon D3 automatically bumps up the exposure and the manual states that one can use a white or gray card.

Using the MacBeth color checker with ACR, it is recommended to use the 2nd brightest neutral square for WB. The brightest square is not spectrally neutral. With the D3 at base ISO, I find that I can get good WB with darker patches. ACR will not allow WB from an area exceeding a certain luminance, since it is possible that some channels might be clipped.

Regards

Bill
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digitaldog
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« Reply #29 on: February 23, 2011, 08:55:09 AM »
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In other words, 5000 degrees kelvin is the same color light no matter what it's coming from.

Any value specified in degrees Kelvin is a range of colors. Many colors of white correlate to 5000K. IOW, its somewhat ambiguous. See the line running from the green to magenta axis that says 5000? ANY color along that line could be properly defined as 5000K.




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What a custom white balance does is set the camera white balance to the exact lighting that's present.


IF the camera had some kind of Spectrophotometer or could measure the SPD of the illuminant, that would be the case.
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Andrew Rodney
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« Reply #30 on: February 23, 2011, 08:56:59 AM »
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Using the MacBeth color checker with ACR, it is recommended to use the 2nd brightest neutral square for WB. The brightest square is not spectrally neutral.

Also because depending on the product making the DNG profile, it might pop an error (too bright).
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Andrew Rodney
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« Reply #31 on: February 23, 2011, 08:58:12 AM »
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The rockstar Flash on your site ensured I went no further.
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donaldahood
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« Reply #32 on: February 23, 2011, 10:11:35 PM »
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Hey medium cool.
HaHa, I have to agree on the rockstar flash thing, even though I own the company. (I'm 50 and feel like somewhere along the line I lost grip with something). I asked the web kids why they couldn't put on some blues or at least classic rock, but oh well.
That brings up an interesting point though. When I go to a website and music is going, especially the sappy music most portrait studios have on their opening page, I frantically hunt the mute button. How does everyone feel about flash and music on a web site?  I'd like to know for our own site.
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Donald
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mediumcool
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« Reply #33 on: February 23, 2011, 11:39:20 PM »
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Hey medium cool.
HaHa, I have to agree on the rockstar flash thing, even though I own the company. (I'm 50 and feel like somewhere along the line I lost grip with something). I asked the web kids why they couldn't put on some blues or at least classic rock, but oh well.
That brings up an interesting point though. When I go to a website and music is going, especially the sappy music most portrait studios have on their opening page, I frantically hunt the mute button. How does everyone feel about flash and music on a web site?  I'd like to know for our own site.

I have taught multimedia and made websites, and am older than 50!

Since it is a business, anything added to your (or any other’s) site scope should have to justify its existence in improving the experience and/or aiding access.

Flash sometimes has its place for heavily-interactive sites, particularly those very much about music and video, but for general usage, HTML5 can do a surprising amount of animation and interactivity, and such sites will work on iPhone, iPod touch and iPad. If you use Flash only, you will not have these people as visitors.

People diss Steve Jobs for not supporting Flash on iDevices; I agree with him, as I have still to see any portable device run Flash well without slowing everything to a crawl and stunting battery life. And it’s crap on the Mac too, sucking up CPU time and threads.

Your “web kids” (or at least one of them) is/are proficient in Flash (hey, I used to teach this too) and therefore would feel impelled to use Flash whether it makes sense or not. I sense reversed baseball caps here, but that’s a cliché …
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ErikKaffehr
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« Reply #34 on: February 24, 2011, 12:40:38 AM »
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Hi,

There are a couple of reasons to avoid Flash, one is that some of disable it! Flash can really suck down a computer and you may even not know that it is running.

The other things is that if I check out a website it perhaps has my attention for seven seconds. So do you want to show some relevant information in those seven seconds so I stay around reading it or have me waiting for some Flash application to load.

Best regards
Erik

Hey medium cool.
HaHa, I have to agree on the rockstar flash thing, even though I own the company. (I'm 50 and feel like somewhere along the line I lost grip with something). I asked the web kids why they couldn't put on some blues or at least classic rock, but oh well.
That brings up an interesting point though. When I go to a website and music is going, especially the sappy music most portrait studios have on their opening page, I frantically hunt the mute button. How does everyone feel about flash and music on a web site?  I'd like to know for our own site.
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donaldahood
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« Reply #35 on: February 24, 2011, 02:33:52 AM »
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OK guys, thanks for the info. It makes sense that if one is not selling music or music related stuff, nor are they selling a service that the music would invoke a mood or feeling, that music wouldn't have a place on the website. (Plus the fact that is slows down a computer). I have removed the flash intro from the website. The products are photography tools, and there's no mood that needs to be generated. It's point blank products, that either work or not.
Now go look at our website, and don't worry about being bombarded with metal. (Personally I'm a big John Lee Hooker fan).
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Donald
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