Archived from groups: rec.photo.digital (
More info?)
On Fri, 14 Jan 2005 23:19:01 -0700, "Jay Beckman" <jnsbeckman@cox.net>
wrote:
>
>"paul" <paul@not.net> wrote in message
>news:VPednRmmJsSdNnXcRVn-pg@speakeasy.net...
>> Canongirly wrote:
>>>
>>>> Shouldn't correcting WB after the fact (without RAW) be as simple as a
>>>> cool/warm slider? Twiddling RGB (or CMYK) is a whole lot more
>>>> complicated. Why doesn't photoshop have a simple cool/warm slider
>>>> adjustment?
>>>
>>>
>>> PS-7: on the menu bar at the top of the screen,
>>>
>>> Edit/Adjustments/Hue-Saturation, then play to your hearts content
>>
>>
>> Hue adjustment cycles through a rainbow, not a simple warm/cool range.
>>
>> It is very confusing.
>>
>> I just don't understand. It's not like I know better: I'm clueless how the
>> WB could be so simple.
>
>Paul,
>
>Allow me to offer some info from the world of TV production that may help
>explain white balance.
>
>Most important thing to bear in mind: WB is not fixable by adjusting HUE.
>
>In TV we rely on two specific scopes that allow us to properly set up TV
>cameras before a broadcast:
>
>-Waveform Monitor (it's actually a scope)
>-Vector Scope
>
>The Waveform shows us relative luminance (in tens of units) from zero to 100
>units of video. We use this to set how bright the whites will be, how dark
>the blacks will be and where the mid range or gamma will be. In Photoshop,
>this equates to adjusting the hightlights, shadows and mid tones. During a
>show, this scope is where we watch the effect of how open or closed the
>camera iris's are.
>
>Color set up uses the aforementioned Vector Scope and I think you'll be able
>to make the connection with a little explanation.
>
>Picture a TV station that has signed off for the night. They often put up
>the test pattern known as "Color Bars." "Bars" (as we call them) allow us
>to make sure that each primary and secondary color we use in TV is at the
>right frequency and the right modulation. A Vector Scope has a circular
>display consisting of a central dot (more on this in a moment) and six boxes
>around the edge into which yellow, cyan, green, magenta, red and blue will
>fall and show up as individual dots when all is set up correctly.
>
>Now, there are two other dots with which we are concerned. One should show
>us a specific lack of luminance (black) and a specific lack of chroma
>(white.) We know each color falls into a specific quadrant of the display,
>so if we see that the very center of the signal is off center say, toward
>green or toward blue, then we know our white balance and/or our black
>balance is off and we can add or subtract some red/blue/green to get that
>centroid back in the middle of the display.
>
>In the "old days" of color photo printing, you would adjust
>cyan/yellow/magenta levels to white balance a print before exposing the
>paper. In TV we use red/blue/green instead. IIRC you can set up Photoshop
>to work in CYK instead of RBG if that it your preference.
>
>This is why you cannot fix a WB problem with hue. Hue just spins the entire
>pallette clockwise or counter clockwise directly around your white/black
>center. If your center is off toward green, then if you adjust the hue, you
>just get a greenish picture that can be made greener yet or pinker but your
>white balance is still off toward green.
>
>My favorite tool for fixing white balance issues in still photos is the
>pallet of tools in Photoshop Elements called "Color Variation." CV allows
>you to selectively add or subtract red/blue/green in any or all of the
>highlites, midtones and/or shadows and this will allow you to combat a
>black/white balance that is being pulled off center.
>
>This may qualify as overkill post of the week (maybe month) but I hope it
>helps. Just remember to think of where your white/black center is. With
>color temp issues, sometimes adding a layer of 2 or 3% worth of a solid
>orange or blue frame can help warm up or cool off an image that was shot too
>cold (in Shadow) or too warm (in Tungsten.)
>
>Feel free to ask any questions and I can maybe simplify this even farther.
>
>Regards,
>
>Jay Beckman
>Chandler, AZ
>Amateur Photog
>Freelance Video Technician
>
I am a retired TV tech from the UK. We were in and at it as soon as
colour started in UK. At a radio (&TV) show I was hailed by one of
the people on the BBC stand. I had bought all the equipment that I
thought necessary, like updating the scope to 100Mhz getting a Philips
signal generator and a colour bar generator. I therefore thought I was
ok. However I was shown a portable flourescent tube which was to be
used on service. The tube was calibrated at 6500 degrees Kelwin and
graduated in about 6 blocks down to black.
That was said to be a necessety for setting up a television correctly.
As you can imagine, the black and dark greys were easy to set but the
white was another kettle of fish. I was advised to go and look at
various manufacturers display and find the one I liked the best and
then compare with the rest, all displaying the test card. The
difference was immense - I reported back to BBC and then they told me
where to obtain what in our shop was named as a monochrome stick.
All sets in the shop was set up using that stick and staff was told to
make the customers aware that we had all sets tuned to the same
station to show that there was no difference from one set to another
and tell a waivering customer to go elsewhere and then ask the sales
person to switch all their sets to the same station to compare from
one set to another. Even from the same factory they could not be
relied on to be right.
We made a lot of sales like that and now some 40 years or more down
the line I am going to get one of the monochrome sticks out of the
shed and try to set white balance from that. I have had trouble with
my Canon S1 which would not photograph a Bourgainvilla bush coming up
with the same colours as my Olympus 2100 UZ or the Pentax Optio S.
My site
http
/www.members.iinet.net.au/~borge contains a exe file
obtained from Irfan View at
http
/www.members.iinet.net.au/~borge/Flowers.exe. Beware, that site
will download the Flowers.exe to your usual download folder where you
can call it up and see the difference from one camera to the next.
Display shows Camera in the top left of the three pictures.
I shall try to adjust the Canon today using the monochrome stick and
let you know the result.
B.Pedersen Latitude -31,48.21 Longitude115,47.40 Time=GMT+8.00
If you are curious look here
http/www.mapquest.com/maps/latlong.adp
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