Go Back   Steve's Digicams Forums > Digital SLR and Interchangeable Lens Cameras > Canon EOS dSLR

Reply
 
Thread Tools Search this Thread
Old Jul 19, 2004, 2:16 PM   #11
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

Alex Campuzano wrote:
Quote:
What about the color values (numbers) when I put my cursor over the gray area? Where should they fall?
FYI: http://www.bradhinkel.com/Color%20Co...ray%20card.htm
NHL is offline   Reply With Quote
Old Jul 19, 2004, 3:22 PM   #12
Member
 
Alex Campuzano's Avatar
 
Join Date: Jun 2003
Posts: 42
Default

NHL,

Thanks for that link. I learned a few things there. The one I'm still wondering about is can I use the same image with the gray card to bring my exposure back into line? I shot these granite slabs with the AV setting and a small aperature (f16 - 22). The lightness of the gray cards vary from image to image, so I need to know what Photoshop values are equal to an 18% gray card?

Does that make sense?


Alex Campuzano is offline   Reply With Quote
Old Jul 19, 2004, 3:48 PM   #13
Senior Member
 
Join Date: May 2003
Posts: 577
Default

twcoffey wrote:
Quote:
Barthold,
The reason the grey card works is that grey is made up of equal levels of Red, Green and Blue and that is by definition when "White Balance" is achieved. However, not all things that look to your eyes grey are actually balanced therefore be sure to use a standard calibrated card.
Ted
Thus all that really matters is that you get something (white or some shade of gray) in your scene that to your eyes looks neutral. Calibrate your camera to that color, and then the picture will come out looking good. Yes, I know its more correct to use an official gray card where each of R,G and B are balanced, but its not necessary.

Barthold
barthold is offline   Reply With Quote
Old Jul 19, 2004, 4:16 PM   #14
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

Alex Campuzano wrote:
Quote:
... The one I'm still wondering about is can I use the same image with the gray card to bring my exposure back into line? I shot these granite slabs with the AV setting and a small aperature (f16 - 22). The lightness of the gray cards vary from image to image, so I need to know what Photoshop values are equal to an 18% gray card?

Does that make sense?
Make sense but:

1. There is no fixed numbers: The values of the grey card are not absolute, but they are tied to your lighting sources... Correct? Isn't this why you need to do the WB in the first place. Beside the same lighting can change depending on whether you 1st turned it on or left on for a long time (sunlight changes color during the day too).

2. The lightness can varies, and it's normal... It's the result of the camera automatic Av metering. The level adjusment in Photoshop should take care of this, ie the color balance will not be affected.
-> If it's a controlled lighting source you should be able to turn the camera to 'M' and transpose the Av settings over. All subsequent shots will then be fixed.
... or you can meter off the Grey card like HawkEyes have suggested! :-)

3. You can use the ‘correct gray card' as described in the above steps to bring the remaining pictures back in-line irrespective of their lightness from the 1st picture. This is equivalent to using different shades of grey cards (they may have different brightness but they are still neutral) as in the previous link.
NHL is offline   Reply With Quote
Old Jul 19, 2004, 9:06 PM   #15
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

Attached below is a greyscale.

Download it to the PC and use the Photoshop's eyedropper color sample tool to click on each shade and see what the "lightness of the gray cards" translate to.

Color is described as (R,G,B) with (0,0,0) being black and (255,255,255) being white. As long as the 3 numbers are equal we still have neutral grey with the shade getting lighter as the numbers grow larger.

The lighting source will color theses greys (or white) one way or another... More red will have larger R number, and more blue will have a larger B, or combination of both. Our goal is to bring theses color back to neutral (ie equal) and not how large or how small theses numbers are because a picture can be high-key (or low-key).

BTW http://www.graphic-design.com/Photos...s/getgray.html
Attached Images
 
NHL is offline   Reply With Quote
Old Jul 20, 2004, 7:27 PM   #16
Senior Member
 
Join Date: Oct 2002
Posts: 123
Default

It all depends on your purposes. If you are looking for accurate rendition of skin tones then careful balncing is necessary but for most purposes the color balance can be off to a considerable degree and not harm the image and in many cases might even enhance it. You may not want perfect color balance. You might be aiming for a warmer or colder image. For example, if you want to capture the orange-yellow light of the setting sun on your subject then you don't want to white balance to the scene but to set it to something like normal daylight. Another example would be to capture incandescent lit scenes or candle lit scenes using a daylight setting to create the warm glow . Another might be to create a blue cold image of a snow scene by setting the balance on warmer.
twcoffey is offline   Reply With Quote
Old Jul 20, 2004, 8:27 PM   #17
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

Here's one more one way to skin the cat:
http://digitalartsphotography.com/instructions.htm
NHL is offline   Reply With Quote
Old Aug 5, 2004, 12:34 AM   #18
Member
 
Join Date: Jul 2004
Posts: 42
Default

HawkEyes wrote:
Quote:
Hey I have an idea, if you want to check the white ballance shoot a white card and save the grey card for it's intended purpose, setting the exposure. That is what I would do anyway. Different strokes, more than one way to skin a cat!
I agree. Check out:

http://www.luminous-landscape.com/tu.../dig-exp.shtml

It's a two step process:
-Set the white balance (White card)
-Correct for the gray balance exposure shift (with the gray card)
Cooly-o is offline   Reply With Quote
Old Aug 5, 2004, 10:08 AM   #19
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,547
Default

Cooly-o wrote:
Quote:
It's a two step process:
-Set the white balance (White card)
-Correct for the gray balance exposure shift (with the gray card)
No one have disagreed that they are two separate steps... Just that you can do both with the same card!

Check it out yourself:
-Set the white balance (Gray card)
-Correct for the exposure (with the gray card)
... then tell us if you find a difference :idea:

ie either White or Grey should work for the white balance because their color are 'neutral', but only differ in intensity!
NHL is offline   Reply With Quote
Old Aug 5, 2004, 1:08 PM   #20
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

Three ways I have seen discussed recently (other than using a photgraphic gray or white card):

1. Set custom white balance with a Pringles Can lid held directly in front of the lens, pointing at the light source. The lid is translucent.

2.Use two or threecoffee filters stacked to set white balance

3. Use this product: http://www.expodisc.com/

I cannot vouch for any of these methods. I'm only passing along what I've seen discussed.


JimC is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 1:23 PM.