Re: Correcting Colour in Photoshop

ian lincoln wrote:

> "Gordon Moat" <moat@xxxxxxxxxxxxx> wrote in message
> news:432081BC.465CA0EA@xxxxxxxxxxxxxxxx
> > ian lincoln wrote:
> >
> >> "Gordon Moat" <moat@xxxxxxxxxxxxx> wrote in message
> >> news:431F436E.2408B0E4@xxxxxxxxxxxxxxxx
> >> > Bandicoot wrote:
> >>
> >> The best way to get a print that matches your screen is to do the
> >> necessary
> >> editing in photoshop then save as jpeg or tiff. Then use the easy print
> >> or
> >> print quicker software that came with the printer. This seems to work
> >> even
> >> using third party inks and papers.
> >
> > Not necessarily replying to you Ian, but to Peter. This type of statement
> > is
> > exactly what I meant by wasting my time trying to explain proper work
> > practices. I am not criticizing what you are doing, but it does show that
> > you
> > are happy with a very simple approach. With that in mind, what reason does
> > someone have to try to do better, or understand how to do better.
>
> I have tried various colour profiles in photoshop. I have tried most of the
> options for the print drivers. I keep going back to the supplied software
> as it is designed and profiled for that specific printer in mind. When
> going to manual it warns that some settings will affect quality. I have
> gone through 50 sheets of paper. Even in contact with someone with a
> similar printer who has spent money on profiling and calibration.
>

Good morning Ian,

I wish I could give you some simple solution. I have looked at the issues of
profiling and simple calibration, and the problem remains that these are not
consistent solutions. Too many things can affect inkjet prints. The level of
humidity, which set of inks, a certain batch of paper being slightly different
from another batch, down to even slight changes in ambient lighting.

>
> Colour settings=
> U.S prepress defaults
> working spaces
> RGB=adobe 1998
> cmyk =us web coated (swap)v2
> gray Dot gain 20%
> spot dot gain 20%
>
> If you have advice for this page and other settings for what comes out of my
> camera to end up on the printer then let me know.
>
> Even epsons own site has no helpful information.

Unless you want to invest in a RIP, a photospectrometer, and learn more about
CMYK, CcMmYK and CMYKog then there are few things you can do. The best you can
hope for is to slightly increase your chances of a more predictable outcome.

Buy a Kodak Q-13 and photograph it under somewhat repeatable lighting
conditions (known flash set-up, or daylight). The Q-13 contains RGB and CMYK
patches. When you open this file in PhotoShop, make sure the Info palette is
visible, then select the colour picker tool (eyedropper). What you will be
doing is measuring the proper colour in each square. Set palette options on the
info palette so that one is RGB (or Actual) and the other is CMYK. Even if you
have a six or eight colour printer, it will still be using CMYK, so you need to
get those values as close as possible.

The adjustments done in PhotoShop can be recorded into an Action. That way, you
can just play back the action for images done under very close to the same
lighting conditions. Obviously, you could end up with a different action for
very different lighting, such as morning, afternoon, dawn, dusk, cloudy,
overcast, etc. People with direct digital cameras might do well to just stay on
daylight white balance, and actually use filters on front of the lens to
compensate (yes, just like using film)(there are good reasons why this works
better, especially on most current D-SLRs).

My suggestion for how to do adjustments is to use the Hue/Saturation Panel. You
need to have the Colour palette visible, and keep it set to HSB (or HSL)
sliders. Once the panel is open, any tool in use will become an eyedropper
(colour picker) when placed over the image. Select the colour square first, and
only adjust one at a time. I suggest starting with the CMY squares; if you can
get them adjusted in RGB mode (or LaB mode), then you are ahead of the game.
Unfortunately, you might need to convert to CMYK mode to get the adjustments to
work out properly. You can adjust the RGB squares in CMYK, and in fact might
get better results; one suggestion is to change Red, we usually think of R as
100% M and 100% Y, but there is a better way to do this. Red is a tough colour
to get looking vibrant on prints; the problem is that Magenta is a much
stronger printing colour (ink) than Yellow. What we can do is fake a brighter
Red; if you know how to do this in LaB mode, you are ahead of the game, but
there is an easier to understand way to do this in CMYK. When in CMYK mode,
adjust the Red square to be 100% M, 100% Y, and 10% to 20% C (Cyan). The extra
Cyan ink will make the red appear to be brighter and more vibrant.

Okay, so you do not have a RIP, and your printer driver only likes RGB files
being fed to it. Convert your CMYK file back to RGB. Then you need to do one
more check on the Green and Blue squares, and do very slight adjustments using
Hue/Saturation only, and watch values on the Info and Colour palettes. Only
adjust Red if you are not using the enhanced Cyan adjusted Red. Also, when
adjusting for any colour square, do not feel bad if getting a 100% reading is
out of reach, just try to get it above 90%, and minimize any other colour
intrusion (mix) to under 10%.

So you might be wondering about the Grey scale adjustments. If you want to do
that, my suggestion is to keep these as a separate action. The idea of trying
to balance out a Grey scale is to eliminate any colour cast at any grey value.
In reality, you might get close, though at some point either colour film or a
direct digital camera will show some colour cast at some grey value. The best
you can hope to achieve is to get close, or slightly improve the initial
capture. Whether it is a scanner, or a digital imaging chip, the filtering used
to separate Red, Green, and Blue uses various strength dyes, which will
influence the balance of some grey values. While it might seem that an LED
set-up like Nikon scanners might avoid that, the reality is that intensities of
the Red, Green, and Blue LEDs varies slightly, so there will still be some
change in some grey values. Any adjustments done in RGB mode should strive to
push each grey square to have equal RGB values (adjusting in CMYK or LaB mode
is tougher). The suggested adjustment tool is Curves, and you should be using a
Lock-down Curve, then adjust each channel separately while watching the Info
palette.

Wow, lots of work . . . there is always something more you can do. When dealing
with paper, many people expect the white of the paper to be 100% brightness,
though the reality is that many are more like 92% brightness. If you can find
out the percentage brightness, then you can adjust your white point in your
image files to better match the paper. I had a rough time trying to find this
information from Epson, and then only for a few papers. Another complication of
this method is that brightness and whiteness values can differ on many papers.
Anyway, using the colour picker tool and the shift key, place a selection point
at the brightest spot on your image file, in our test model that is the white
square on the Q-13. Then use the Levels panel and only manually adjust the left
most (white point) slider. The adjust is based on the paper brightness value,
in other words, if you have a 95 brightness paper, then adjust the point you
selected to be 5% on the Info palette. If you only want to do this one, and no
Grey scale adjustments, then this will work in either CMYK or RGB mode. It can
be more useful to set your Info palette options to read CMYK, then do this
adjustment while only watching the K value change from 0% to 5%.

After all that, you will have one or more Actions you can use to adjust any
files. The colours should come out more consistent, and closer to actual. Of
course, different ink batches, humidity, paper variation, and lighting changes
can still affect the final print, but you should be less far off on most
outputs.

Anyway, this is the lowest cost option to become more consistent. I got this
method working due to delivery of problem files from some clients for design
projects I have worked on. I also use a variation of these methods for work I
have done after adjusting file from rental digital cameras I have used for
work. A small Q-13 target is enough, and you can find these for near $US 20.00.

Feel free to ask questions, though I will state up front that I am not sharing
my LaB mode adjustment methods, nor am I willing to relate my other adjustment
methods. I am happy to explain things more if something I wrote does not make
sense.

Ciao!

Gordon Moat
A G Studio
<http://www.allgstudio.com/technology.html>


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