By Ian Lyons




A Computer Darkroom Review


As each week passes the number of digital cameras grows and with them the demand for ever greater colour accuracy. Likewise, were ICC profiling was once the domain of only high-end capture devices costing many 10's of thousands of dollars it is now common, albeit still relatively expensive.


Introduction and discussion

Why do we even need to bother profiling a camera given that the reviews of these new all-singing-all-dancing cameras would have us believe that their colour accuracy is nothing short of perfection? Any owner of the original and very popular Nikon D1 digital will give you plenty of reasons, likewise owners of just about every other digital camera on the market. I own both a Canon EOS D30 and a Nikon CoolPix 950, and there are occasions when certain colours as captured by the camera are quite simply nowhere near the real colours. It should also be noted that the Nikon and Canon Digital SLR's are not unique in having difficulty rendering some colours accurately, the phenomena effects every digital camera in one way or another.

Over recent months I've been fortunate to evaluate a number of software packages designed specifically for the purpose of profiling digital cameras. I've also tried a few were the vendor still uses the IT8 target. So far as the latter type goes they are a waste of time, effort and money. Profiling a digital camera requires a completely different type of target to that designed for scanner profiling.

Digital cameras capture colour information from many different types of material and so the IT8 target with its target patches based upon only three colourants is virtually useless. The colours of the Macbeth ColorChecker and Macbeth ColorChecker DC charts have properties whereby the colourants used have the reflectance spectra similar to real world objects such as skin, foliage, etc. and so will replicate their response under a wide range of lighting conditions. Likewise the neutral patches, which have a relatively flat reflectance spectra and thus remain neutral under virtually any lighting conditions.

Nevertheless and contrary to what some would have us believe; digital camera profile and editing software is not all created equally, nor is it foolproof. The quality of the resulting profiles isn't simply a matter of the software being used. The choice of target; i.e. Macbeth ColorChecker or Macbeth ColorChecker DC, and  the lighting conditions under which it is captured will all play a part in the quality of final profiles. Don't assume that the more expensive ColorChecker DC chart will always be better, it won't, and don't assume that all digital cameras are equally easy/difficult to profile, they aren't. For many the time, effort and expense of creating custom profiles for their digital cameras is just not worth it. For others it isn't a subject open to discussion it's something they have no choice but to do. Hopefully the above discussion and following review will go someway to helping the reader better understand the reasons behind, and the processes involved.

inCamera Professional in use

So how do we go about creating an ICC profile for our typical digital camera sing inCamera Professional? The procedure is fairly straight forward and to a large extent requires little or no previous experience. The steps are as follows:

  1. White balance the camera using a Kodak Gray Card. The process is usually described in the camera user manual.
  2. Determine the exposure for the scene (lighting falling on target). Typically can mean anything up to 1/2 fstop or more above the metered exposure when measuring off the Kodak gray card. It's probably best to capture a series of images at different exposure values above and below the gray card value.
  3. Take a picture of a Macbeth ColorChecker or ColorChecker DC chart. It's important that the whole chart is included and that it's evenly illuminated and free from reflections. All camera automatic exposure features should be set to OFF.
  4. Transfer the images to the computer and Open inCamera Professional and choose New>Digital Camera Profile.



Depending upon the actual target used it's now simply a matter of selecting the target image file, choosing the matching reference file and cropping the target image so that it fills the frame.


ColorChecker Chart

GretagMacbeth ColorChecker Chart


The above screenshot shows the less expensive Macbeth ColorChecker chart (approximately $60), which comprises 6 greyscale tones and 18 coloured patches. As discussed above, many of the patches represent natural objects of special interest such as: skin tones, foliage and blue sky. Macbeth describe the target patches as follows: "The squares are not only the same colour as their natural world counterparts, but also reflect light in the same way in all parts of the visible spectrum".


ColorChecker DC

GretagMacbeth ColorChecker DC Chart


The screenshot show above demonstrates the feature whereby inCamera Professional can be configured to ignore the eight glossy coloured patches of the Macbeth ColorChecker DC chart. In theory, the inclusion of these patches helps the profiling software determine how the camera behaves when capturing more saturated colours. The reality is that these patches can actually result in a less than optimal profile for no other reason than reflections are almost impossible to avoid. On those occasions that I did manage to capture a reflection free image of the target there was no doubt as to the improvement in the quality of the profile, but such occasions were extremely rare. A quick check of forums such as the "ColorSync" and "Colour Theory" mailing lists confirms that the glossy patches are the single most likely reason for failure when profiling a digital camera. Pictographics are to be congratulated for enabling the user to avoid them, although it is always wise to check the quality of the profile with them included.

To assist in getting the most accurate crop of the target image the user should mouse click each of the corners, in turn, whilst holding down the Option/Alt key. This activates the Zoom box Once the target image has been cropped it's simply a matter of pressing the Save button; creation of the profile will be almost instantaneous. Note: at this point the profile has been saved in Pictographics proprietary (.Prof) format and so we must do a little more work before our task is complete.

Contd. on next page...


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