Go Back   Steve's Digicams Forums > Digicam Help > General Discussion

Reply
 
Thread Tools Search this Thread
Old May 13, 2010, 5:08 AM   #11
Senior Member
 
musket's Avatar
 
Join Date: Jan 2007
Posts: 2,782
Default

Very good explanations are given above and if you want the room AWB then it might look like this
Attached Images
 
musket is offline   Reply With Quote
Old May 13, 2010, 5:30 AM   #12
Super Moderator
 
Mark1616's Avatar
 
Join Date: Oct 2005
Posts: 7,397
Default

Quote:
Originally Posted by musket View Post
Very good explanations are given above and if you want the room AWB then it might look like this
I'm not sure that is correct as the camera should be selecting the flash WB as soon as the flash is used when in auto. I've not experienced a photo with any camera where the subject exposed by flash has been cold such as this when in auto.
__________________
Any problems with a post or thread please use the report button at the bottom left of the post and the team will help sort it out.

Have fun everyone!


See what I'm up to visit my Plymouth Wedding Photography
site or go to my blog.
Mark1616 is offline   Reply With Quote
Old May 13, 2010, 8:11 AM   #13
Senior Member
 
musket's Avatar
 
Join Date: Jan 2007
Posts: 2,782
Default

Quote:
Originally Posted by Mark1616 View Post
I'm not sure that is correct as the camera should be selecting the flash WB as soon as the flash is used when in auto. I've not experienced a photo with any camera where the subject exposed by flash has been cold such as this when in auto.
Unlikely that the camera would do that, that was just an illustation achieved in PP
musket is offline   Reply With Quote
Old May 13, 2010, 8:17 AM   #14
Super Moderator
 
Mark1616's Avatar
 
Join Date: Oct 2005
Posts: 7,397
Default

Cool, just checking, don't want people to think they need to keep switching the AWB to Flash every time flash might be used, that would give us all brain ache..... mine hurts enough most of the time
__________________
Any problems with a post or thread please use the report button at the bottom left of the post and the team will help sort it out.

Have fun everyone!


See what I'm up to visit my Plymouth Wedding Photography
site or go to my blog.
Mark1616 is offline   Reply With Quote
Old May 13, 2010, 8:29 AM   #15
Senior Member
 
billy's Avatar
 
Join Date: May 2004
Location: Ohio USA
Posts: 1,733
Default

Quote:
Originally Posted by Jan851 View Post
I have not had much success with the Custom WB, but it's probably operator error. I'll try to refine that technique for the non-flash pics.
Jan,

If you shoot photos in that gym often, you could take a look at the ColorRight products. They help you quickly set a more natural WB using your camera's custom or manual setting. I worked with their Pro model HERE, and was quite impressed. If that unit seems expensive, they do have a more affordable model as well (which I will be testing this month hopefully).

It would work with your flash as well. Just a thought, good luck either way.

-billy
billy is offline   Reply With Quote
Old May 13, 2010, 10:04 AM   #16
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

The way a camera sets a custom white balance is by measuring the temperature of the light it's seeing (assuming it's seeing a "neutral" target.

So when you take a custom white balance reading from a neutral target (for example, a white or gray card), and the camera sees differences between the proportions of red, green and blue it's measuring in the lighting you're shooting in (because of the temperature of the lighting), it can determine what RGB multipliers to apply to the images you take in that lighting.

Virtually all camera manufacturers use the same technique (store the actual RGB Multipliers they want to apply later), and apply those multipliers to the images if you're shooting in JPEG; or store them in the metadata if you're shooting in raw, so they can be applied by a raw converter later if you want to use the "as shot" white balance.

For example, it may be applying multipliers like 2.15x, 1.1x, and 1.27x to the red, green and blue channels, respectfully, during the demosaic process.

Some camera also store a color temperature reading in the EXIF metadata, too (so you'll know the temperature of the lighting the camera thought it was shooting in). But, what the conversion process is actually doing is applying a set of multipliers to the RGB channels (the idea is to increase or decrease the values for each color channel so that they look correct in the lighting you're shooting in).

Both mid gray and white are good for setting a custom white balance, because they have equal parts of red, green and blue. For example, pure white measures as 255, 255, 255 when looking at a correctly balanced white patch; whereas a mid gray may measure as 128, 128, 128; or an 18% gray card may measure closer to 117, 117, 117.

For White Balance purposes, it doesn't make any difference (as they'd all contain the same proportions of red, green and blue; and should reflect each color equally.

All the camera is trying to do is figure out the correct RGB multipliers needed to make all 3 colors appear to have equal values with a neutral target. For exposure purposes, it can make a difference (if you're trying to set exposure by measuring reflected light, it's best to use something closer to 18% gray, since the camera is more interested in overall brightness -- but, for setting a Custom White Balance, it's not relevant).

The way products like the ColorRight Pro that Billy mentioned work is by diffusing light through a gray medium of some type. That way, the camera can adjust the RGB multipliers used for the image you take in the same lighting.

But, with flash in a larger gym, you'd have the same problems using that type of product as you would any other type of product to set a custom white balance with.

The issue is that light falls off dramatically as flash range increases, and you can't use a more powerful direct flash (able to light up the background) for a closer subject (because that would make the closer subject overexposed).

So, if you have a closer subject (as in the photo in your first post in a large gym), and white balance is correct for that subject when using a flash; then the background elements will not be correct (they're too far away to be effected by the light from the flash and the white balance needed for them will be different).

That's because the temperature of the lighting in a typical gym environment is going to fall somewhere 3000k and 4000k. But, the temperature of the flash is usually closer to 5500k (and your closer subject will be lit mostly by the flash, but the further away subjects will be lit mostly by the gym lighting).

If you try to "average" the temperature between them, then neither will be correct.

Although a tool like Billy mentioned can work with Flash in mixed lighting, it's designed to work with a subject at a specific range (i.e., if you're shooting a subject from 6 feet away, that's where you'd point your camera to set a custom white balance for that subject), provided you're using similar exposure settings. That's because the light from the flash and light from ambient light sources would make up the same percentage of the exposure for a given subject at a given distance using the same exposure settings (whereas the flash power in proportion to ambient light sources would change with a different subject at a different distance).

But, when you have subjects close to the flash (as in your sample); and subjects much further away; there is no way any tool can give you the correct white balance for both when using a flash, unless you use gels or similar tools, as Mark1616 mentioned in his first post to this thread; or have a flash that's powerful enough to illuminate an entire gym (which you're not going to get in a large gym unless you have multiple strobes, positioned in a way so that lighting is even from them throughout the gym).

The idea behind using colored gels (or diffusers with colored domes to reflect light from that color through the dome), is to transform the light from the flash so that it more closely matches the temperature of the lighting you're shooting in.

That way, you don't have differences in lighting temperature between your foreground and background.

For example, an amber gel will allow the light from your flash to more closely match tungsten lighting, and a green gel will allow your flash to more closely match the temperature from flourescent lighting. You can find gels of various colors to more closely match a given lighting (so that the light from the flash matches the lighting you're shooting in).

Then, you can accurately set a custom white balance for that type of environment using a tool like the one Billy mentioned (or using a gray or white card to set it).

But, in your case (unless you use a flash with colored gels, or convince the gym to install lighting closer to the temperature of the flash), you wont' be able to get *both* a closer subject illuminated mostly by flash, and distant background subjects illuminated mostly by gym lighting, that are correctly color balanced, no matter what tool you use to set White Balance (because the temperature of the lighting will be different for both). You'll either need to choose one or the other for setting white balance, or try to average temperature between them (then, neither will be correct, but you may have less difference between them).
JimC is offline   Reply With Quote
Old May 13, 2010, 10:42 AM   #17
Administrator
 
Join Date: Jun 2003
Location: Savannah, GA (USA)
Posts: 22,378
Default

Shorter Answer:

No tool for measuring White Balance can work and give you accurate colors for both closer subjects illuminated by a direct flash *and* far away background subjects lit by artificial lighting at a different color temperature (as the temperature of the lighting will be *very* different between the closer and further away subjects), unless you modify the light from the flash (using colored gels or similar diffusers) to match the temperature of the background lighting.

While a tool like the Colorright Pro can work in mixed lighting for flash photos, that's only when the subjects you're measuring and shooting have the same proportion of ambient light and light from the flash (which is not going to be the case in your example shooting a closer subject in a large gym with a direct flash). So, you could use that type of tool to set a custom white balance for a specific subject (e.g., the closer girl shot with flash). But, don't expect the background (not lit by the flash) to have correct colors.
JimC is offline   Reply With Quote
Old May 13, 2010, 7:46 PM   #18
Junior Member
 
Join Date: May 2010
Posts: 15
Default

I think I understand the difficulty in the picture. At some point, cameras will have two white balance settings...subject and background...wishful thinking maybe? Until then, since I am only using a point and shoot, I guess I will have to try to minimize it... but in the end, just live with it. My first try will be to perfect the non-flash, but since I looked at the small prints, the IQ is not as good as the flash.

Fortunately, we don't spend the majority of our time in the gym!!!

Thanks for the help! I'm learning a ton...and may step into dSLR territory when I get better!
Jan851 is offline   Reply With Quote
Old May 14, 2010, 2:20 PM   #19
Senior Member
 
musket's Avatar
 
Join Date: Jan 2007
Posts: 2,782
Default

Here's another version without flash
Attached Images
 
musket 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 8:14 PM.