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inCamera

PROFESSIONAL 3

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.

Profile Checker

Once a profile for the digital camera has been created it is always a good idea to check how it behaves. The screen shot below shows a results for a profile based upon a Canon EOS D30 capture of the Macbeth ColorChecker DC chart. The information contained in this example goes well beyond the simple graphical comparison of the chart that is provided by most other profile software vendors.

With inCamera Professional the tones and colour characteristic's of each and every patch are compared against the reference values and the patch with greatest error is highlighted. In this case it is one of the white patches (J6), and it can be seen that the error is quite small at a "Delta-E of 0.5". The overall colour difference is even smaller at a "Delta-E of 0.1" Run your mouse across any coloured patch and the input data for the profile and its reference value will be displayed.

Note: Delta-E is a measure of colour difference in CIE Lab. Under ideal viewing conditions a Delta-E of 1 represents a just perceptible colour difference to the human eye although in less than ideal lighting values of between 2 or 3 can be considered as equivalent. 

Profile Checker

Profile Checker

It's also possible to measure the amount of noise found in the captured image. Again in the example shown above (Canon EOS D30 in linear raw mode) the values are quite low. Although not shown here it is possible to represent the actual noise levels within the image using a graphical overlay. This will show a coloured dot over each patch that exceeds the specified level of noise.

We can also review the overall uniformity of the lighting conditions under which the original target image was captured. This feature is only available when using the Macbeth ColorChecker DC chart. The uniformity of lighting appears to have quite a large impact upon the quality of the resulting profile and being able to check it helps considerably in determining whether it is better to simply retake the photograph again or depend upon simple editing of the profile.

Exporting the Profile

Once the user is happy that the profile has been created it's simply a matter of Selecting the Export command. Again, inCamera Professional offers a wider range of options for saving an ICC profile. 

Export Profile

Export Profile

The profile can be saved in either 8-bit or 16-bit precision, Tonal Compression technique and the if these are not enough the user can also choose the Rendering Intent. There are a number of other choices for adaptation (e.g. XYZ Scaling or Bradford Transform)  to be found under the Options button. I recommend that you choose XYZ scaling as it is more compatible with Mac and PC appications. Again on-line help is available for quick reference and the comprehensive user manual should also provide more than ample guidance. Speaking of the user manual, this is a mine of information and the fact that it can be downloaded, for free,  from the PictoColors web site should not be ignored.

Ideally you should try the profile on a range of images prior to deciding if any edits may be required. Typically the image will appear somewhat flatter (less contrasty) than you would normally expect, however, this is easily corrected using a very simple S-curve in Photoshop. If you feel the need for further guidance on the operation of inCamera Professional Pictographics provide a number of tutorials on their web site

Profile Editor

For those occasions when you find the newly created profile isn't quite accurate enough the profile editor provided with inCamera Professional is available. It is both powerful and easy to use. The user has the ability correct for tonal and colour discrepancies within the profile along with hue, saturation and brightness. A question often asked of ICC profile software is - why would we need to edit the profiles? In the case of digital camera profiles it could something as simple as poor white balancing when capturing the target image or as is more likely uneven illumination. Another possibility and one that impacted upon my trials is the fact that neither the basic ColorChecker chart or the more expensive DC version has any sample patches that exceed a Lab lightness channel value of 96. In a gamma 2.2 working space Lab 96 for the lightness channel equates to roughly RGB=244. This falls far short of pure white and can often lead to really odd colour imbalances, especially when the sensor behaves in a non-linear fashion at or near saturation (RGB=255) (e.g. the Canon EOS D30 magenta whites when images are grossly overexposed).

Editor

inCamera Professional Profile Editor

The above screenshot shows a before and after edit view of the image with the profile edited to give a neutral colour balance. PictoColors call this method of removing global colour casts "Neutral Pointing". With this example I had deliberately corrupted the highlight patches of the target so that they were excessively red. In doing so I was trying to replicate a problem I noted with only marginally overexposed images from at least two high end digital cameras. Notice that the edited profile corrects for the error without impacting upon the remaining tones. The process of Neutral Pointing is very simple. The user simply identifies areas of the image that should be neutral and clicks these with the sample tool. For complex images it's best to use the scale method as shown above. However, the inCamera Professional profile editor also offers a method that is similar in operation to the "Variations" tool in Photoshop for those situations were finding neutral points is difficult.

As with the cropping feature described above it is possible to zoom into a section of the image. Simply holding down the Option/Alt key and clicking the relevant section of the image with the mouse curser cause inCamera Professional to zoom into that section of the image.

Occasionally a profile will have the effect of clipping the white or black points of some images or it might even be the case that some images were grossly underexposed or overexposed. Using the Black and White point adjustments it is possible to modify the profile so that the image data is spread more effectively.

B&W Point

Black and White Point Adjustment

As with global colour casts, making adjustments for hue shifts that impact upon only one colour is fairly straight forward. Pictographics have chosen to use the Hue (colour) Ring as the basis for these edits.

Selective Colour Editor

Selective Colour Adjustments

As noted in the previous section it's probably best not to make edits to a profile based upon only one image as doing so might result in a profile that is image specific (not what we would normally intend). I find that cycling through a range of different images helps identify those hues that might need some refinement. The process of editing a hue requires only that the user clicks the the appropriate hue in an area of the image with the sample tool and then drags the anchor point on the hue ring in the direction that fixes the problem. It's also possible to increase/decrease the chroma (saturation) and Lightness of a specific hue. So long as the appropriate monitor profile has been selected in the inCamera Professional setup procedure the display will be very accurate. An on-line Help function is available via the "?" icon on the top right hand corner of the editor panel.

Conclusions

inCamera Professional is considerably more flexible and more accurate than the other digicam profiling software products that I have evaluated up to date. The ability to ignore the troublesome glossy patches of the Macbeth ColorChecker DC chart is something that other vendors should consider VERY seriously. The included profile editing tool with in-built softproofing is much more than a simple profile tweaking tool since it allows the user to exercise a great deal of control over how the profiles will behave when applied to images. The inclusion of the editor sets inCamera Professional apart from other profiling tools.

Whilst the results that I obtained from inCamera Professional are very good they are not perfect. That said  inCamera Professional succeeded were others had failed in so far as I finally managed to produce high quality ICC profiles for the Canon EOS D30 in its linear raw mode. Profiling any digital camera in its linear condition is extremely difficult not least because the images are VERY dark and never being anywhere near full-scale. Having learned a few lessons along the way with inCamera Professional I was able apply the same methodology with the other software packages, although not always as successfully and NEVER with the Macbeth ColorChecker DC chart, inCamera Professional was uniquely successful in this regard due to its ability to ignore the glossy patches.

In publishing this review I am conscious that there are be many elements of the inCamera Professional software package that I have not been able to cover in any detail. These include the very powerful Monitor calibration and profiling tool and the ability to import an edit digital camera ICC profiles from other vendors.

 

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