Previous Page     Page 3 of 4     Next Page
Contd.
 

4. Colour Settings

The previous section concentrated upon how we see colour on the monitor and how accurate that representation of colour actually is. The "Color Settings" menu option found under the "File" menu is where we effectively tell "Photoshop" what red, green, blue, cyan, magenta and yellow actually look like, and how we want the colour management system therein to operate on these colours.

 

Image

 

(i) RGB Setup

The RGB setup dialog is where we define the Photoshop RGB "Work Space". Just to confuse matters it’s also known the "Editing Space", or "Colour Space", I'll be using the three terms interchangeably.

The work space selected here is normally considered "device independent" (i.e. independent of scanner, monitor or printer devices), and allows Photoshop to attach a specific colour meaning to our RGB data.

Remember also that unless you specify otherwise the RGB work space (profile) selected by you here is the profile that will be saved with your file (i.e.; "tagged").

Before we begin selecting our preferred RGB work space I will dispel a commonly held misconception, namely that the gamma and white point selected for the RGB work space must be the same as we have chosen when calibrating our monitor, wrong!, simply because the two are NOT related. There is absolutely no reason why you should keep both compatible.

 

Image

 

There are nine "Canned" RGB colour spaces supplied as standard with Photoshop 5, each of which is based upon industry standards. There is also the option to select your "monitor space" (i.e. Monitor RGB) or define your own "Customised" RGB work space.

The selection of Monitor RGB is not recommended since it is not "device independent", but most importantly, monitors cannot display a considerable part of the gamut of CMYK output devices such as our inkjet printers.

 

Image

 

Of the nine "canned" RGB colour spaces there are only three that are truly useful to most of us printing to inkjet printers, namely:

  • Adobe RGB (1998) – based upon a gamma of 2.2 and a White Point of 6500K, which is broadly compatible with daylight in shade. This colour space comes very close to encompassing the entire CMYK gamut, although it has some difficulty with greens. Its gamma value of 2.2 ensures adequate separation of shadow detail is maintained.
  • ColorMatch RGB – this RGB colour space is based upon a gamma of 1.8 and a White Point of 5000K. It is also widely used by Mac users, and has slightly narrower colour gamut than Adobe RGB. Its main drawback relates to the gamma value of 1.8, which can cause some posterisation problems in shadow areas. That said it is still a perfectly acceptable workspace on either the PC or Mac platforms.
  • sRGB – this RGB colour space is similar to Adobe RGB above in that it is based upon a gamma of 2.2 and a White Point of 6500K. However, the colour gamut of this space is somewhat limited and can only be recommended for use with the 4-colour range of inkjet printers from Epson, Canon, HP, etc. It is also widely used for web pages, etc.
With the "Custom" option we can define our own RGB colour space, although this doesn’t come highly recommended. That said there is one custom colour space that has almost become an industry standard, i.e. "BruceRGB". The specification for this work space is as follows:-
  • White Point = 6500K
  • Gamma = 2.2
  • Red Primary xy = 0.6400, 0.3300
  • Green Primary xy = 0.2800, 0.6500
  • Blue Primary xy = 0.1500, 0.0600
This colour space has all the advantages of Adobe RGB (1998) but doesn’t suffer the problems associated with greens to the same extent. This colour space is now highly favored by users of the 6-colour consumer inkjet printers such as those supplied by Epson.

Remember to use the "Save" button after you create this profile (this will ensure that it is retained for future use). You can give the profile any name you like, although I recommend BruceRGB, especially if you propose to share your files with others, since there’s a greater chance that they will be able to handle your file without conversion.

The last setting that you can make in the RGB setup dialog is – "Display Using Monitor Compensation" (DUMC). With this feature activated we are instructing Photoshop to carry out an "on-the-fly" conversion of the image data from our selected RGB "work space" to our "monitor space", using the information contained in your customised monitor profile. So now we see why it is so essential that the monitor be calibrated correctly. It should also be noted that this "on-the-fly" conversion does not impact upon, or damage the image data in any way.

If you find that your prints don't match the monitor image (i.e. to dark, to light, etc.) then try switching DUMC off. If the screen more closely matches the print with DUMC off then your monitor calibration is "broken". I recommend that you try the method I described for monitor calibration which is based upon the "Adobe Monitor Profile".

For Photoshop users who share files with others, and especially across platforms (PC to MAC and vice versa) the following should be noted:

 

"If you open a file that has been colour adjusted in a gamma 1.8 workspace into a gamma 2.2 workspace without conversion the resulting on screen image will appear darker and more contrasty than it would have otherwise have done. Conversely, if you originally colour corrected a file in a gamma 2.2 workspace and then open it in gamma 1.8 workspace without conversion then the image will appear flat and light."

The moral here is that unless you have very good reasons stopping you converting to your own workspace then you should always allow the colour space conversion to take place.

(ii) CMYK Setup

For the most part this dialog is of no interest to those of us who concentrate solely on an RGB workflow. That said there is one "gem" buried within the CMYK settings dialog that anyone using "Custom" printer profiles simply must take heed of, i.e. "soft proofing" your RGB printer. Unfortunately, it doesn’t appear to work too well with Epson’s new "Standard" printer profiles.

 

Image

 

Soft proofing your RGB printer is based upon a very complex procedure developed by Mark Hamburg of Adobe, my thanks to Andrew Rodney for giving us access to the Photoshop Actions that make the whole process much simpler to implement.

 

Image

 

So, rather than try to explain it myself I’ll let Andrew Rodney do it for me: -

"Photoshop 5 has no RGB soft proof (unlike the CMYK Preview/Soft Proof feature). That means that while having a calibrated display is VERY important, you are not looking at your RGB file with an output simulation. There IS a way to trick Photoshop into providing a soft proof for RGB files and you will generally see a much closer screen to print match. This is mostly affecting out of gamut (very saturated) colours. The process of converting an RGB output file into a CMYK profile for soft proofing is long and complex. However, you can find a PDF with the recipe and a Photoshop action on my Web page:-

(http://www.digitaldog.net/tips.html)

that allows you to load into the CMYK setup, a modified RGB profile for your printer and then use the CMYK preview (Ctrl+Y) to redraw the screen to get a closer match. Of course the quality of all this depends on the quality of the output profile and how well your display really is profiled and calibrated."

 

(iii) Grayscale Setup

This dialog allows us to define our grayscale working space by stating whether it is based on RGB neutral values (i.e. equal values of Red, Green and Blue) or simply based on Black ink. If the latter is chosen then the dot gain curves defined in the CMYK dialog are used. Remember to switch "Off" RGB soft proofing feature described above if you are using that feature.

 

Image

 

If you are using a "Custom" printer profile there is a lot of merit in converting your grayscale images back to RGB before outputting to the printer. Although, it is worth trying both options, and settling one you prefer rather than blindly following convention or even my suggestions.

(iv) Profile Setup

I’ve heard it said that unless you share your image files with other users or have been using an earlier version of Photoshop then the Profile Setup feature is surplus to requirements, nothing could be further from the truth.

The Profile Setup dialog is in fact fundamental to determining how (or even whether) Photoshop acts upon images when they are "opened" or "saved". If you set the various options incorrectly you could potentially destroy an image and never even know that you’ve done so.

It performs two functions, namely:-

 

> It offers you a method of ensuring that images get converted into your working space, and

> It lets you embed an ICC profile (or "tag") within the file that describes the workspace in which the image was created.

As can be seen from the screen-grab below, the dialog is separated into three distinct sections, "Embed Profiles", "Assumed Profiles", and "Profile Mismatch Handling".

The Embed profiles section is fairly straightforward in that by checking the boxes we are effectively telling Photoshop to automatically embed our workspace profile within the file when we save the image. By default all the checkboxes are normally "On". It is recommended that you leave this section of the Profile Setup in its default state, the exception being when you open a printer calibration Test target (typically those used with Device Profiling Packages such as WiziWYG, EZcolor, etc.). With calibration targets it essential that you don’t allow the image to be saved (usually by accident) with your work space profile, so its better to be safe than sorry, with printer calibration images make sure "Embed Profiles" is "Off". However, remember to set it to "On" again once you finish with the printer calibration.

 

     Page 3 of 4    
Contents on this site: Ian Lyons © 1999 - 2017. All Rights Reserved