Re: Correcting Colour in Photoshop


"Gordon Moat" <moat@xxxxxxxxxxxxx> wrote in message
news:4325D142.15FA392F@xxxxxxxxxxxxxxxx
> 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.
>
..
>
> 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>

Thanks gordon. For now i have purchased the photoshop cs book for digital
photographers by Scott Kelby. Decided to start at the begining and work my
way along. Already found some useful tips regarding the built in browser.
Made a contact *** for a jewel case and saved it. Moving photos around.
Before i had my windows explorer window open and using the normal file and
open browser. This is far more efficient. This book was one of the most
expensive but it was the only one that tackled photoshop from aphotographers
point of view. Others covered web graphics and animation etc so would have
been a false economy. I also have how to cheat in photoshop but that is
largely cutting corners for existing intermediate to advanced users and
largely covers graphic design. I might be able to use that book once i have
completed this one.


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