Tech Support Grab Bag

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This reserved article originally appeared in CHROMiX ColorNews Issue 29 on October 17, 2007.

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October, 2007 This Month's Feature Article:

Contents

Tech Support Grab Bag

by CHROMiX's Patrick Herold and Steve Upton

This month, instead of writing an article as we usually do, we thought we'd try to address some of the questions we're asked on a regular basis. As always, please remember that, if you have a specific question you'd like us to address, please send it in and we'll do our best to publish it, and its answer.

Photoshop, Mac and Epson combinations

(Pat Herold)

Every once in a while, we get a call from someone who is following the proper procedures for using their custom printer profile, but getting poor results in their actual prints. In the article from ColorNews Issue 24 <http://www.colorwiki.com/wiki/Printer_to_Match_my_Screen>, we explained what to look for if your printer is not printing as expected. If you are following all of these guidelines and the color is still not right, are you using a Mac computer to print with Photoshop to an Epson printer? These three don't always play nicely together when it comes to printer profiles, so here are a few more things to check:

(See Editor's note below.)

EDITOR'S NOTE: Since the release of OS 10.6 (Snow Leopard), the profile to use is sRGB.icc. For older operating systems, you would use the "generic RGB.icc" profile. For more information on this, and an alternate workaround click the following link from Luminous Landscape:
EDITOR'S NOTE: These same workarounds are listed with a little more detail in issue #40 of the CHROMiX ColorNews under the heading "Tech Notes":

How can I make one printer look like another?

(Pat Herold)

This is a basic question, but to get a simple answer depends on whether the profiles for your two printers are accurate. IF the profiles for your two printers are good quality, then all you need to do is to use Photoshop to convert to the profile of the printer you want to emulate. Then, print on your other printer as usual.

For example, let's say you want to want to print on your HP Z3100 so that it looks the same as your Epson 2200. You would convert your image to the Epson 2200 profile. Then print that image to the HP Z3100 using the regular Z3100 profile. This assumes that these two profiles are accurately representing what these printers are putting out.

To streamline this process, set up the Epson 2200 profile for soft proofing, then select this soft proofing setup as the 'source' color when printing. Then Photoshop will perform the conversion to the Epson 2200 profile and onto the HP printer profile on the fly.

ColorThink Pro tip - Fine-tune a profile

(Pat Herold)

Did you know you can use ColorThink Pro to "fine-tune" profiling? Say you have an image to print that has some problem colors in it, and you'd like to make a printer profile that specifically samples those colors so that the profile will have more detailed information about how to treat them. This is not a "one-click" procedure, but it's very useful when you want to improve a profile without taking the dangerous step of editing it.

The worksheet in ColorThink Pro allows you to select colors in an image using the eye dropper or target marque tools. Those color selections are added to a colorlist, and that colorlist can be saved as a reference file - which can then be added into your regular reference file and made into a new, expanded target. This can be used with any printer profiling software that accepts custom targets.

Procedure

  1. Open an image into ColorThink
  2. Convert the image to your device's color space using your existing device profile (or pre-convert the image in Photoshop)
  3. Using the eyedropper tool, click on the colors you wish to sample. This will start populating a colorlist. Remember that you can zoom in on an image by enlarging the worksheet or using the magnify tool (in overlay or slice image modes only.)
    1. Alternatively select the target marque tool and choose 'custom' as the size, then select the number of sample points you want.
    2. Click and drag to select a portion of your image, and ColorThink will sample many points from an evenly-spaced grid.
  4. Save the rightmost color list by clicking on "<untitled list>", and "Save List As...".
  5. Choose destination, and click the drop down box to choose the device space of your printer.
  6. Name the new colorlist and save it.
  7. Open the new colorlist in a text editing program, or a spreadsheet program like Excel.
  8. Open the reference file for your profiling target in the same program.
  9. Copy and paste the color information from your new colorlist onto the end of your profiling target reference.
  10. Bring your target reference into the Testchart Generator of MeasureTool (if you have that function enabled), or Gretag / Xrite's ColorLab program (if you don't have MeasureTool).
  11. Create a new testchart using the normal procedures.

Your profile will now be built with additional sampling in the area of the color space you selected. With ProfileMaker, we have found this can sometimes drastically improve flesh tone transitions and other common issues.

How do internal-calibration screens differ from regular displays?

(Steve Upton)

A number of high-quality LCD displays available today make use of "internal calibration" technology and we find that this feature, while very useful, confuses and confounds.

A quick background on screen calibration

In a conventional CRT or LCD display system, calibration of the display mostly takes place in the computer's graphics card. When you run your screen calibration software, it displays many different color patches on screen and measures them using your calibration hardware (puck). Typically, the largest number of patches are for the calibration of the screen. This stage is where the behavior of each individual RGB color channel is measured, and then curves are loaded into the graphics card in order to achieve the gamma or L* curve you requested AND achieve neutral grays from black to white. The balance of maximum RGB values may also be set to achieve a white point other than the one the display shows in its uncalibrated state. (We strongly suggest altering CRTs on their front panels rather than having the software do this.)

As you may know, any time you pass numbers through a curve, you lose some of them (unless it's a flat curve). In a high-bit system (more than 8 bits per channel), this may not be a big deal, but in a display system using 8 bits per channel, it can be a big problem. 8 bits per channel is barely enough to display smooth transitions across all colors on a display - some feel it's not enough. If your display requires significant curving to bring it into calibration, then many of the 256 possible values become unavailable. This shows up as posterizing in displayed images.

If you want to explore this concept interactively, take a look at Bruce Lindbloom's Levels Calculator here: [http://www.brucelindbloom.com/LevelsCalculator.html]

One method to get around this problem is to find a graphics card with high-bit calibration curves.... good luck. Rumors abound that they exist (they used to) or that they soon will, but they are rare indeed.

Another method is to move the calibration function into the monitor itself. In this case, the video card's curves are set to gamma 1.0 (flat), so any outgoing values are unaltered and no precision is lost. Then the calibration software produces curves for the monitor's internal tables. The secret? These tables have 10-14 bits of precision.

How does this help? Well, the calibration software can alter the behavior of the display quite a bit before running up against the problem of losing precision in the 8-bit data coming from the computer. It can also spend more time (and patches) on the gray-balancing of the display, producing more neutral grays across the full range and also making the transitions smoother.

Do these displays work?

Definitely!

Do you need to use software that can take advantage of these curves?

Definitely!

Obviously, the software shipped with the display will support this level of calibration. Some other packages - ColorEyes Display Pro and Eye One Match are notables - will also support internal curves on many displays. I'd check with the software folks about it supporting your display before buying the software, just to be sure.

[Editor's note: Eye One Match will perform "DDC" corrections to compatible
high-end monitors, but does not interact with their internal graphic tables. -PH]

Now... the clincher..

How can I tell if I have one (or that it is calibrated correctly)?

Well, the curves that are internal to displays are not easy to get a hold of. In most cases, the curves themselves appear to be stored inside the display itself. But there is one quick way to check (on the Mac):

  1. Open the ColorSync utility
  2. Find your display profile among the listed display profiles
  3. Double-click to open it
  4. Click on the vcgt tag in the profile

Note the shape of the curve and whether or not it has a gamma of '1.0'

If the curve is not completely flat then your display calibration is taking place in your graphics card. If it is flat, and the profile was created using calibration software and an instrument, then you can be assured that the calibration is taking place within your display's tables.

On Windows, it may not be so easy to perform this test.

If you are a ColorThink user, open the profile into the Profile Inspector and select the 'vcgt' tag. ColorThink will report that the curve is defined by 'a formula' if it is flat. Otherwise it will be described by the number of points in the curve. The Windows Color Control Applet does not report this kind of information. I believe that ColorShop X will report this information if you use it.

Does this mean that my display is a '14 bit' display?

No! Definitely not!

You could say that it is a display with '14 bit calibration' but it is certainly not a 14 bit display. To be a 14 bit display you would need 14 bits per channel of image data coming from Photoshop, through a supporting graphics card, and then out to a supporting display. And we're a fair ways off from that! Also, this does not mean that you will have 14-bit grays. You will still only have 256 discrete levels of gray - they will simply be well calibrated levels of gray without any of the 8 bits lost due to calibration.

I hope this helps clear up any confusion you may have about these displays.

Matching two displays - with a virtual twist

(Courtesy of Eric Walowit)

How do you get your Parallels Windows XP display to match a Mac's OS X display?

For those wishing to match "two" displays between XP and OSX on a single machine with a single screen, here is how to do it with ColorEyes Display Pro (CEDP):

  1. Install CEDP on OSX only (do not install CEDP under Parallels XP).
  2. Calibrate and profile under OSX normally.
  3. Copy the profile just created over to Parallels/XP, install, and select it from the Display Control panel.
  4. Disable any LUT loading application from the XP startup folder, or anywhere else for that matter.
  5. Repeat anytime the monitor is recalibrated and profiled.

This works under Parallels/XP but not VMWare/XP, and should work with most any monitor calibration solution.

A bit cumbersome but a small price to pay.

The Parallels/XP method should be obvious, but the wrinkle is that VMWare just doesn't support video LUTs, OS-level color management, or selection of a monitor profile even if no calibration is required.

Bummer because VMWare seems to be superior in every other way.

(Thanks to Derrick Brown and Chris Murphy for their helpful suggestions.)


Thanks for reading,

-Patrick Herold and Steve Upton

CHROMiX


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