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How to capture exact RBG or CMYK color numbers?



 
 
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  #1  
Old April 4th 13, 09:17 AM posted to rec.photo.digital
Jennifer Murphy[_2_]
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Posts: 127
Default How to capture exact RBG or CMYK color numbers?

I am trying to get a true color photograph of an oil painting. Because
of the propensity of the shiny and irregular surface of the painting,
reflection has been a problem, requiring some creative lighting set ups.

I have several photos taken with different cameras using differnet
settings and setups. On my computer screen, they each have slightly
diffenet colors.

The image will be sent to a printer 3,000 miles away. I would like to be
able to ensure that the printed colors are as true as possible to the
actual painting. It occurred to me that if I had the exact RGB and/or
CMYK numbers for a few spots on the painting, the printer should be able
to reproduce it pretty accurately.

What's the best way to get the exact RBG or CMYK numbers for the colors
on the actual painting? Is there a color wheel I can buy that I can hold
up to the painting? Is there some electronic scanner that will show me a
readout?
  #2  
Old April 4th 13, 09:48 AM posted to rec.photo.digital
bugbear
external usenet poster
 
Posts: 1,258
Default How to capture exact RBG or CMYK color numbers?

Jennifer Murphy wrote:
I am trying to get a true color photograph of an oil painting. Because
of the propensity of the shiny and irregular surface of the painting,
reflection has been a problem, requiring some creative lighting set ups.

I have several photos taken with different cameras using differnet
settings and setups. On my computer screen, they each have slightly
diffenet colors.

The image will be sent to a printer 3,000 miles away. I would like to be
able to ensure that the printed colors are as true as possible to the
actual painting. It occurred to me that if I had the exact RGB and/or
CMYK numbers for a few spots on the painting, the printer should be able
to reproduce it pretty accurately.

What's the best way to get the exact RBG or CMYK numbers for the colors
on the actual painting? Is there a color wheel I can buy that I can hold
up to the painting? Is there some electronic scanner that will show me a
readout?


Measuring the colours "exactly" will have the same lighting
and reflectance issues as your photograph, I'm afraid.

You can quite readily calibrate your shot
by including a known target in the photograph,
or shooting the target under the same conditions
as your photograph.

Proper targets aren't super-cheap.

Here's a handy page about this:

http://www.aff.org.au/AFF2_Eckert_co...al_summary.htm

BugBear
  #3  
Old April 4th 13, 10:20 AM posted to rec.photo.digital
DanP
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Posts: 90
Default How to capture exact RBG or CMYK color numbers?

On Thursday, April 4, 2013 9:48:48 AM UTC+1, bugbear wrote:

Proper targets aren't super-cheap.

Here's a handy page about this:

http://www.aff.org.au/AFF2_Eckert_co...al_summary.htm



BugBear


Buy 2 identical targets, have one delivered to you and the other at the point of printing, shot the target next to the painting with the same lighting and same white balance, print the target shot by you and have it compared with the one delivered.

DanP
  #4  
Old April 4th 13, 10:33 AM posted to rec.photo.digital
Jennifer Murphy[_2_]
external usenet poster
 
Posts: 127
Default How to capture exact RBG or CMYK color numbers?

On Thu, 04 Apr 2013 09:48:48 +0100, bugbear
wrote:

Jennifer Murphy wrote:
I am trying to get a true color photograph of an oil painting. Because
of the propensity of the shiny and irregular surface of the painting,
reflection has been a problem, requiring some creative lighting set ups.

I have several photos taken with different cameras using differnet
settings and setups. On my computer screen, they each have slightly
diffenet colors.

The image will be sent to a printer 3,000 miles away. I would like to be
able to ensure that the printed colors are as true as possible to the
actual painting. It occurred to me that if I had the exact RGB and/or
CMYK numbers for a few spots on the painting, the printer should be able
to reproduce it pretty accurately.

What's the best way to get the exact RBG or CMYK numbers for the colors
on the actual painting? Is there a color wheel I can buy that I can hold
up to the painting? Is there some electronic scanner that will show me a
readout?


Measuring the colours "exactly" will have the same lighting
and reflectance issues as your photograph, I'm afraid.


Aha. If I shine a red light on it, it will look different than if I
shine a green or pure white light on it. So the only way to get the
"true" colors of the object is to take it to a carefully controlled
environment where it is illuminated by a perfectly balanced light
source. This business is maddeningly complex and nuanced.

You can quite readily calibrate your shot
by including a known target in the photograph,
or shooting the target under the same conditions
as your photograph.

Proper targets aren't super-cheap.

Here's a handy page about this:

http://www.aff.org.au/AFF2_Eckert_co...al_summary.htm


What if I lower my expectations or, at least, make them soemwhat more
realitic. Instead of saying I want to get the "exact" RGB numbers,
suppose I say that I want to get the RGB numbers for the painting as it
looks hanging in my living room under midday ambient light?

Could I then get a color wheel and match up 4-5 spots on the portrait to
spots on the wheel and record the RGB numbers? Or it there some sort of
handheld scanner that will read out RGB numbers?

I couldn't find anything, but I didn't know what to search for. I did a
search for "rgb scanner" and came up with some sort or hot car
accessory.
  #5  
Old April 4th 13, 11:26 AM posted to rec.photo.digital
Martin Brown
external usenet poster
 
Posts: 821
Default How to capture exact RBG or CMYK color numbers?

On 04/04/2013 10:33, Jennifer Murphy wrote:
On Thu, 04 Apr 2013 09:48:48 +0100, bugbear
wrote:

Jennifer Murphy wrote:
I am trying to get a true color photograph of an oil painting. Because
of the propensity of the shiny and irregular surface of the painting,
reflection has been a problem, requiring some creative lighting set ups.

I have several photos taken with different cameras using differnet
settings and setups. On my computer screen, they each have slightly
diffenet colors.

The image will be sent to a printer 3,000 miles away. I would like to be
able to ensure that the printed colors are as true as possible to the
actual painting. It occurred to me that if I had the exact RGB and/or
CMYK numbers for a few spots on the painting, the printer should be able
to reproduce it pretty accurately.

What's the best way to get the exact RBG or CMYK numbers for the colors
on the actual painting? Is there a color wheel I can buy that I can hold
up to the painting? Is there some electronic scanner that will show me a
readout?


Measuring the colours "exactly" will have the same lighting
and reflectance issues as your photograph, I'm afraid.


Aha. If I shine a red light on it, it will look different than if I
shine a green or pure white light on it. So the only way to get the
"true" colors of the object is to take it to a carefully controlled
environment where it is illuminated by a perfectly balanced light
source. This business is maddeningly complex and nuanced.


Yes. It depends on the colour temperature of the nominally "white" light
too. Some things like Nd doped glass look radically different under
sunlight, incandescent or fluorescent lighting. Alexandrite glass
ornaments exploit this curious property of certain materials:

http://www.20thcenturyglass.com/glas...mium_glass.htm

You can quite readily calibrate your shot
by including a known target in the photograph,
or shooting the target under the same conditions
as your photograph.

Proper targets aren't super-cheap.

Here's a handy page about this:

http://www.aff.org.au/AFF2_Eckert_co...al_summary.htm


What if I lower my expectations or, at least, make them soemwhat more
realitic. Instead of saying I want to get the "exact" RGB numbers,
suppose I say that I want to get the RGB numbers for the painting as it
looks hanging in my living room under midday ambient light?


Use the dropper function inside PSPro or Photoshop to sample the colour
and read back its RGB value. CMYK values will depend on the colour model
and gamma used to transform from RGB to the smaller CMYK space. Some
software will warn you where parts of the image will clip in the print
media colour space. Certain programs don't do a good job on this.

Could I then get a color wheel and match up 4-5 spots on the portrait to
spots on the wheel and record the RGB numbers? Or it there some sort of
handheld scanner that will read out RGB numbers?

I couldn't find anything, but I didn't know what to search for. I did a
search for "rgb scanner" and came up with some sort or hot car
accessory.


There are some proprietary cards with a hole in that have a bunch of
reference colours on and some clever shade matching software that will
allow a close enough by eye match to a single colour.

Designed by mix your own paint manufacturers to allow DIYers to box
themselves into nightmare corners with bespoke custom paints. eg

http://www.dulux.co.uk/colours/colourclick/index.jsp

Proper colour reference cards are available for photography but they are
not cheap and against a textured painting with varnish you are up
against multiple problems so they may not help you all that much.

--
Regards,
Martin Brown
  #6  
Old April 4th 13, 02:42 PM posted to rec.photo.digital
Mayayana
external usenet poster
 
Posts: 1,514
Default How to capture exact RBG or CMYK color numbers?

| What's the best way to get the exact RBG or CMYK numbers for the colors
| on the actual painting? Is there a color wheel I can buy that I can
hold
| up to the painting?

Pantone colors are the standard for printing. You can
buy fandecks at graphic supply stores. I think they go
for somewhere around $60-$100. But you'll need a very
good eye for color and a close match in lighting. In my
experience it's maddeningly difficult to match a color
chip even to wall paint when I know that the color on
the wall is an exact match to one of the chips. There's
just too much difference in texture, gloss, etc. and that
changes the perceived color. (If you really look at a the
walls of a room in any light you'll see that there are
countless hues and shades -- darker in the corners,
less yellow near windows, more yellow near incandescent
lights, etc.)



  #7  
Old April 4th 13, 02:47 PM posted to rec.photo.digital
Joe Kotroczo
external usenet poster
 
Posts: 170
Default How to capture exact RBG or CMYK color numbers?

On 04/04/2013 10:33, Jennifer Murphy wrote:

(...)
I couldn't find anything, but I didn't know what to search for. I did a
search for "rgb scanner" and came up with some sort or hot car
accessory.


If you're looking for a gadget, the keywords to search with are
"handheld spectrophotometer"...

Good luck.

  #8  
Old April 4th 13, 03:24 PM posted to rec.photo.digital
Mark Storkamp[_2_]
external usenet poster
 
Posts: 23
Default How to capture exact RBG or CMYK color numbers?

In article ,
Jennifer Murphy wrote:

What's the best way to get the exact RBG or CMYK numbers for the colors
on the actual painting? Is there a color wheel I can buy that I can hold
up to the painting? Is there some electronic scanner that will show me a
readout?


Unless it was a paint-by-number kit, I don't understand how you would
expect to be able to do that. Every oil painter I know mixes and blends
colors on their pallet and layers and mixes them on the canvas. I think
the best you can hope for is to have the printer send you samples to
compare to the original, and make adjustments as necessary.
  #9  
Old April 4th 13, 04:47 PM posted to rec.photo.digital
nospam
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Posts: 24,165
Default How to capture exact RBG or CMYK color numbers?

In article , Jennifer
Murphy wrote:

Aha. If I shine a red light on it, it will look different than if I
shine a green or pure white light on it. So the only way to get the
"true" colors of the object is to take it to a carefully controlled
environment where it is illuminated by a perfectly balanced light
source. This business is maddeningly complex and nuanced.


you can white balance for whatever light you use. what you need is a
colour managed workflow, as does your printer.

What if I lower my expectations or, at least, make them soemwhat more
realitic. Instead of saying I want to get the "exact" RGB numbers,
suppose I say that I want to get the RGB numbers for the painting as it
looks hanging in my living room under midday ambient light?


the rgb numbers don't mean anything by themselves.

Could I then get a color wheel and match up 4-5 spots on the portrait to
spots on the wheel and record the RGB numbers? Or it there some sort of
handheld scanner that will read out RGB numbers?


won't work.

your best bet is include a macbeth colour card in the shot, which can
later be cropped out. the printers can adjust the image so the card is
correct, which should mean the painting will be correct. they can then
crop out the card when printing.

I couldn't find anything, but I didn't know what to search for. I did a
search for "rgb scanner" and came up with some sort or hot car
accessory.


i don't see that when searching for rgb scanner.

anyway, search on colour management. that will give you way more than
you ever wanted to know. if you are near a bookstore, the bible is
called real world colour management, by fraser, murphy and bunting.
plan for brain overload.

http://www.colorremedies.com/realworldcolor/
  #10  
Old April 4th 13, 04:47 PM posted to rec.photo.digital
nospam
external usenet poster
 
Posts: 24,165
Default How to capture exact RBG or CMYK color numbers?

In article , Jennifer
Murphy wrote:

I am trying to get a true color photograph of an oil painting. Because
of the propensity of the shiny and irregular surface of the painting,
reflection has been a problem, requiring some creative lighting set ups.

I have several photos taken with different cameras using differnet
settings and setups. On my computer screen, they each have slightly
diffenet colors.


that's expected.

The image will be sent to a printer 3,000 miles away. I would like to be
able to ensure that the printed colors are as true as possible to the
actual painting. It occurred to me that if I had the exact RGB and/or
CMYK numbers for a few spots on the painting, the printer should be able
to reproduce it pretty accurately.


that won't work.

rgb and cmyk numbers by themselves don't mean anything.

What's the best way to get the exact RBG or CMYK numbers for the colors
on the actual painting? Is there a color wheel I can buy that I can hold
up to the painting? Is there some electronic scanner that will show me a
readout?


the way to do this is with a colour managed workflow. you calibrate and
profile your monitor and you also obtain a profile for the printer to
be used. then, what you see will be what the printer sees. otherwise,
you're flying blind.

however, you could include a macbeth colour card in the photo for a
reference, maybe just outside the actual painting. then the printers
can colour balance the image so the card looks correct, and
theoretically, the paining will be as well.

note that what you see on a monitor can't be perfectly matched by a
printer. however, you can soft-proof it on your monitor and get a very
good approximation.
 




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