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07-30-2007, 08:52 PM   #1
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K10D whitebalance question

because i am slightly, marginally colorblind, i take extra care when dailing in my colors. i love the WB functions of the k10d.....

i know with some other brands you should use an 18% gray card to whitebalance on, and with pentax you whitebalance on white.

on both of my pentax's, it seems like the meter reads a little over...its about a 1/3 to 1/7 stop and it causes me to underexpose if i dont adjust.

im wondering if it isnt actually underexposing. i had a thought today that maybe if i try whitebalancing on an 18% gray card that it would take off some of the dull look.

maybe the brand just favors shadows...who knows...

but...now that i want to at least try a custom WB on an 18% gray card and dont have one...what is a good substitue? the inside of my lowepro? a concrete wall?

thanks

07-30-2007, 10:58 PM   #2
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That is a tough one. Our eyes adjust to slight variations in colors that we perceive as neutral, making it difficult to assess whether an object is truly gray or not. On the other hand, white balance is somewhat subjective and any gray object that is at least within a few shades of neutral may be close enough for the human eye. This is an interesting question and I can't wait to hear what others have to say.
07-31-2007, 04:45 AM   #3
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I am slightly confused, You start off on white balance and then shift to exposure.

If you are concerned about exposure you should use a grey card. this is the traditional surface that metering has been compared to.

If you want to adjust white balance you should use white.

If you set your exposure using a white card, you will under expose.

Note on the K10 to set white balance, take a picture of a scene (with the desired lighting), metered normally with a white card in the scene.

without shutting the camera off press the Fn button, and pick white balance. As you adjust, you will see the net result immediately on the image you just took
07-31-2007, 07:19 AM   #4
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im making a relation between common pentax underexposure and the difference between white and gray card whitebalancing.

so ill just try my experiment and get back to the forum.

mitch

07-31-2007, 09:06 AM   #5
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QuoteOriginally posted by MJB DIGITAL Quote
im making a relation between common pentax underexposure and the difference between white and gray card whitebalancing.
There isn't suppose to be one. White Balance affects the colors on the picture, it does not change the amount of light entering the lens that's to be metered for exposure.

To test: Use 2 different predefined white balance settings and meter the same scene at the same spot back to back. Your metered values should be the same.

The primary use of grey cards is for metering. As your camera is suppose to be calibrated to that grey, you meter off the grey card in your desired scene and adjust your exposure till the light meter value is in the middle.
07-31-2007, 10:21 AM   #6
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MJB,

Exposure: Control is on the left. Lever sets Spot, Center Weighted, Averaged. Try each and see what happens. Spot allows the camera to meter exposure exactly where the focus dot lies in the viewfinder. Center Weighted allows the camera to meter an average area around the focus dot.
Average of course, allows the camera to meter all light in the entire scene.

White Balance: Shoot in RAW and you can post adjust. Or take a coffee filter and hold it over the end of the lens. Please don't scratch your glass. Go to Fn, WB, and select custom. While the custom screen is up hit your shutter release. Viola, WB set to scene light. If scene is too dark and not enough light is present, put the filter back in your pocket, do the same Fn deal and take a picture of the closest thing to white or neutral gray that you can find in your scene.

I agree with others that WB has nothing to do with how the Pentax exposes the image.

Good Shooting,

Chuck
08-02-2007, 04:57 PM   #7
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QuoteOriginally posted by MJB DIGITAL Quote
because i am slightly, marginally colorblind, i take extra care when dailing in my colors. i love the WB functions of the k10d.....

i know with some other brands you should use an 18% gray card to whitebalance on, and with pentax you whitebalance on white.

on both of my pentax's, it seems like the meter reads a little over...its about a 1/3 to 1/7 stop and it causes me to underexpose if i dont adjust.

im wondering if it isnt actually underexposing. i had a thought today that maybe if i try whitebalancing on an 18% gray card that it would take off some of the dull look.

maybe the brand just favors shadows...who knows...

but...now that i want to at least try a custom WB on an 18% gray card and dont have one...what is a good substitue? the inside of my lowepro? a concrete wall?

thanks
It does favor shadows, about 1/3 of a stop.

If you're going to set your white balance from a white card you need to dial in +2 EV and make sure the white card is slightly angled towards the light source while filling the frame.

Me personally, I take a picture of the white object with proper exposure and then make a custom XMF file for Adobe Camera Raw so I can use that light source again on future files.
08-03-2007, 06:11 PM   #8
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QuoteOriginally posted by MJB DIGITAL Quote
i know with some other brands you should use an 18% gray card to whitebalance on, and with pentax you whitebalance on white.
I've never heard this before, and my K100D manual says:
Fully display a white or gray sheet of paper in the
viewfinder under the light to adjust white balance.
I would think that being color-neutral is the really important thing, but I can see how the camera's software could work better one way or the other. Can someone explain the situation with Pentax cameras more or give me a reference? Thanks!

08-03-2007, 07:48 PM   #9
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What a jumbled mess you've made of these two subjects.

One uses the 18% gray card to set exposure. More specifically to set a baseline exposure that is repeatable. One still needs to make subject specific adjustments from this baseline based on education and experience. Adequate experimentation is required.

One sets the white balance from a known neutral target. It may be nearly white or some mid-tone gray. What's important is that it is neutral--equal parts of red, blue and green--or very nearly so. White balance must be made under conditions of 'proper exposure', i.e. you need enough light to make the mechanism function.

Kodak made a fine line of 18% gray reflective targets, but they are not neutral and as they age, they become even less neutral. They will serve a very long time for exposure measurements with proper storage. They are less suitable for white balancing.

Several manufacturers make neutral gray targets. Robin Myers Imaging has a nice plastic unit. So does someplace called RawWorkFlow. You can do a fine job white balancing in Post IF you include a neutral target in at least one shot. In an earlier day RWF also made a set of 3 or 4 targets: white, two grays & black for just such a task.

On the fly white balancing is best done with a Myers type card or the hideously expensive ExpoDisk---all coffee filters are NOT created equal. If one strays into video-photography one encounters warm and cool balance targets; pale green and pale magenta casts to otherwise white targets. These are what makes the coffee filter method suspect.

In a pinch one could use the intended print paper as the white balance target-just don't change papers. This is particularly effective in a fully color managed work environment. It's also possible to force a particular white; simply make the intended white object large enough in the viewfinder to cover the small WBing square and set it. YMMV!

QuoteOriginally posted by MJB DIGITAL Quote
because i am slightly, marginally colorblind, i take extra care when dailing in my colors. i love the WB functions of the k10d.....

i know with some other brands you should use an 18% gray card to whitebalance on, and with pentax you whitebalance on white.

on both of my pentax's, it seems like the meter reads a little over...its about a 1/3 to 1/7 stop and it causes me to underexpose if i dont adjust.

im wondering if it isnt actually underexposing. i had a thought today that maybe if i try whitebalancing on an 18% gray card that it would take off some of the dull look.

maybe the brand just favors shadows...who knows...

but...now that i want to at least try a custom WB on an 18% gray card and dont have one...what is a good substitue? the inside of my lowepro? a concrete wall?

thanks
08-03-2007, 07:58 PM   #10
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QuoteOriginally posted by jfdavis58 Quote
What a jumbled mess you've made of these two subjects.

One uses the 18% gray card to set exposure. More specifically to set a baseline exposure that is repeatable. One still needs to make subject specific adjustments from this baseline based on education and experience. Adequate experimentation is required.

One sets the white balance from a known neutral target. It may be nearly white or some mid-tone gray. What's important is that it is neutral--equal parts of red, blue and green--or very nearly so. White balance must be made under conditions of 'proper exposure', i.e. you need enough light to make the mechanism function.

Kodak made a fine line of 18% gray reflective targets, but they are not neutral and as they age, they become even less neutral. They will serve a very long time for exposure measurements with proper storage. They are less suitable for white balancing.

Several manufacturers make neutral gray targets. Robin Myers Imaging has a nice plastic unit. So does someplace called RawWorkFlow. You can do a fine job white balancing in Post IF you include a neutral target in at least one shot. In an earlier day RWF also made a set of 3 or 4 targets: white, two grays & black for just such a task.

On the fly white balancing is best done with a Myers type card or the hideously expensive ExpoDisk---all coffee filters are NOT created equal. If one strays into video-photography one encounters warm and cool balance targets; pale green and pale magenta casts to otherwise white targets. These are what makes the coffee filter method suspect.

In a pinch one could use the intended print paper as the white balance target-just don't change papers. This is particularly effective in a fully color managed work environment. It's also possible to force a particular white; simply make the intended white object large enough in the viewfinder to cover the small WBing square and set it. YMMV!

Actually, Gray cards were developed for Exposure but it really doesn't matter if you use Gray or White. All that really matters is that the RGB values are identical in each color channel because that is what balances the color temp... Everything else is shifted based on this reading.

I've used both Kodak Gray Cards and plain ole white printer paper to which both performed admirably (of course the white card required the +2.0 EV adjustment to get the exposure correct while setting the white balance) under pretty much any condition.

One company out there (whibal) seperates the two but I would be real interested in getting some of the numbers from skin tones in their images; yes their images look good to the eye but do they stand up to the info test?
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