Measuring the Color of White

OK, so I got this Ott Light, a portable desk lamp with a daylight
balanced fluorescent bulb, in order to check my prints and compare them
to the monitor.

But the light seems a little green to my sore eyes, so I am wondering
how I can measure the color temp of it to be sure of what I am looking
at. I'm trying to come up with a scheme of shooting a piece of white
paper with my camera and trying to see what white balance it takes to
correct it to 6500K. But I'm not sure yet how to do that. On my
particular camera, the Oly E20, it doesn't tell you what the actual
color temp is when you white balance it. I do have the option of setting
specific white balances manually, though. So suppose I set 6500, then
shoot the color of the light, then bring it into my photo program, then
measure the RGB values of it? Would that make sense?

Any other ideas on this?

Gary Eickmeier

Gary Eickmeier wrote:
OK, so I got this Ott Light, a portable desk lamp with a daylight
balanced fluorescent bulb, in order to check my prints and compare them
to the monitor.

But the light seems a little green to my sore eyes, so I am wondering
how I can measure the color temp of it to be sure of what I am looking
at. I'm trying to come up with a scheme of shooting a piece of white
paper with my camera and trying to see what white balance it takes to
correct it to 6500K. But I'm not sure yet how to do that. On my
particular camera, the Oly E20, it doesn't tell you what the actual
color temp is when you white balance it. I do have the option of setting
specific white balances manually, though. So suppose I set 6500, then
shoot the color of the light, then bring it into my photo program, then
measure the RGB values of it? Would that make sense?

Any other ideas on this?

If you were to achieve the above, it would lead you to....?

--
John McWilliams

Gary Eickmeier wrote:
OK, so I got this Ott Light, a portable desk lamp with a daylight
balanced fluorescent bulb, in order to check my prints and compare them
to the monitor.

But the light seems a little green to my sore eyes, so I am wondering
how I can measure the color temp of it to be sure of what I am looking
at. I'm trying to come up with a scheme of shooting a piece of white
paper with my camera and trying to see what white balance it takes to
correct it to 6500K. But I'm not sure yet how to do that. On my
particular camera, the Oly E20, it doesn't tell you what the actual
color temp is when you white balance it. I do have the option of setting
specific white balances manually, though. So suppose I set 6500, then
shoot the color of the light, then bring it into my photo program, then
measure the RGB values of it? Would that make sense?

Any other ideas on this?

If you were to achieve the above, it would lead you to....?

--
John McWilliams

This is not intended as a recommendation for this company, but the
following link is on topic and worth a read..

http://www.soluxtli.com/Ott_lite.htm

In summary, daylight is not equal, by a longshot, to any fluoro and you
should expect some problems..

This is not intended as a recommendation for this company, but the
following link is on topic and worth a read..

http://www.soluxtli.com/Ott_lite.htm

In summary, daylight is not equal, by a longshot, to any fluoro and you
should expect some problems..

Gary Eickmeier writes:

But the light seems a little green to my sore eyes, so I am wondering
how I can measure the color temp of it to be sure of what I am looking
at. I'm trying to come up with a scheme of shooting a piece of white
paper with my camera and trying to see what white balance it takes to
correct it to 6500K. But I'm not sure yet how to do that. On my
particular camera, the Oly E20, it doesn't tell you what the actual
color temp is when you white balance it. I do have the option of setting
specific white balances manually, though. So suppose I set 6500, then
shoot the color of the light, then bring it into my photo program, then
measure the RGB values of it? Would that make sense?

Set your camera to 6500 K, shoot a piece of blank paper in light that
truly is 6500 K (direct sunlight is roughly this), then pull it up in
your photo program and balance the colors in the image until the color
of the paper shows as a neutral white (RGB values all the same). Save
these adjustments for subsequent use. That will give you a correction
to apply to get neutral colors whenever you use the 6500 K setting in
6500 K light.

However, I find it easier to just look for something in an image that is
supposed to be a neutral gray, then adjust the colors in the image until
it _is_ a neutral gray. Neutral gray means that red, green, and blue
values are all identical. Don't trust the way it looks on your screen,
since that can vary by monitor and display settings.

--
Transpose hotmail and mxsmanic in my e-mail address to reach me directly.

Gary Eickmeier writes:

But the light seems a little green to my sore eyes, so I am wondering
how I can measure the color temp of it to be sure of what I am looking
at. I'm trying to come up with a scheme of shooting a piece of white
paper with my camera and trying to see what white balance it takes to
correct it to 6500K. But I'm not sure yet how to do that. On my
particular camera, the Oly E20, it doesn't tell you what the actual
color temp is when you white balance it. I do have the option of setting
specific white balances manually, though. So suppose I set 6500, then
shoot the color of the light, then bring it into my photo program, then
measure the RGB values of it? Would that make sense?

Set your camera to 6500 K, shoot a piece of blank paper in light that
truly is 6500 K (direct sunlight is roughly this), then pull it up in
your photo program and balance the colors in the image until the color
of the paper shows as a neutral white (RGB values all the same). Save
these adjustments for subsequent use. That will give you a correction
to apply to get neutral colors whenever you use the 6500 K setting in
6500 K light.

However, I find it easier to just look for something in an image that is
supposed to be a neutral gray, then adjust the colors in the image until
it _is_ a neutral gray. Neutral gray means that red, green, and blue
values are all identical. Don't trust the way it looks on your screen,
since that can vary by monitor and display settings.

--
Transpose hotmail and mxsmanic in my e-mail address to reach me directly.

Gary Eickmeier writes:

OK, so I got this Ott Light, a portable desk lamp with a daylight
balanced fluorescent bulb, in order to check my prints and compare
them to the monitor.

But the light seems a little green to my sore eyes, so I am wondering
how I can measure the color temp of it to be sure of what I am looking
at. I'm trying to come up with a scheme of shooting a piece of white
paper with my camera and trying to see what white balance it takes to
correct it to 6500K. But I'm not sure yet how to do that. On my
particular camera, the Oly E20, it doesn't tell you what the actual
color temp is when you white balance it. I do have the option of
setting specific white balances manually, though. So suppose I set
6500, then shoot the color of the light, then bring it into my photo
program, then measure the RGB values of it? Would that make sense?

Colour temperature has no meaning for sources that are not continuous
blackbodies[1]. Flourescent light spectra are generally extremely
jagged with spikes and discontinuities, this is why there is such a
problem with metamerism with them.

So, in short, fluorescent lights are poison because you *cannot*
correct for the vagaries of a non-continuous spectrum once you have
collapsed your spectrum into three numbers, R, G, and B coordinates.

B

[1] Think of a blackbody as anything which gives off light because
it's heated up enough to glow. An incandescent filament, for
example. Or very very hot helium and hydrogen, as another example.

Gary Eickmeier wrote:
OK, so I got this Ott Light, a portable desk lamp with a daylight
balanced fluorescent bulb, in order to check my prints and compare them
to the monitor.

But the light seems a little green to my sore eyes, so I am wondering
how I can measure the color temp of it to be sure of what I am looking
at.

This doesn't make sense with a fluorescent. What you really need to
know is the colour rendering index, or CRI, and to measure that you
need a spectrophotometer.

According to a web site I'm looking at, the Ott-Lites come in two
kinds, the Task bulb and the True Color bulb. The former has a CRI of
83, which is useless for your purpose. The latter has a CRI of about
93, which is more like what you need for photos.

So which kind of bulb do you have?

Andrew.

Gary Eickmeier wrote:
OK, so I got this Ott Light, a portable desk lamp with a daylight
balanced fluorescent bulb, in order to check my prints and compare
them
to the monitor.

But the light seems a little green to my sore eyes, so I am wondering

how I can measure the color temp of it to be sure of what I am
looking
at. I'm trying to come up with a scheme of shooting a piece of white
paper with my camera and trying to see what white balance it takes to

correct it to 6500K. But I'm not sure yet how to do that. On my
particular camera, the Oly E20, it doesn't tell you what the actual
color temp is when you white balance it. I do have the option of
setting
specific white balances manually, though. So suppose I set 6500, then

shoot the color of the light, then bring it into my photo program,
then
measure the RGB values of it? Would that make sense?

Any other ideas on this?

Gary Eickmeier

I use a color temperature meter (sorry could not resist) some photo
rental places rent these.