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Digital Camera profiling with the SG ColorChecker card
A review of the Eye One Photo SG package from GretagMacbeth
The Eye One Match software from GretagMacbeth supports the creation of digital camera profiles if you have a ColorChecker SG card. This is included in the Eye One Photo SG package. Keith has covered aspects of the various options in other Eye One reviews.
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Topics The What's New Page gives a quick overview of the hundreds of pages of articles and picture on this site. This page is part of the Reviews feature in our Articles and info section |
| In this review Keith also looks at the general question of profiling digital cameras and includes a modified version of Thomas Fors' ACR calibration script that allows you to calibrate Adobe Camera Raw using the SG card rather than the more common original ColorChecker card.
Northlight Images prides itself on its independence when giving advice. We do not sell hardware or software and have no direct commercial links with any of the software or hardware vendors that may be mentioned here. See our Review Policy for more information. |
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Digital Camera colour management
When it comes to colour management for printers and monitors (Eye One links) there is no question about the benefits offered -- but input devices are more problematic. I've covered some of the issues in scanner profiling in another article, but camera profiling is a much more contentious. I've heard the whole exercise dismissed as fundamentally futile, but there is an increasing amount of software designed to do the task.
When you look at the response to light of different wavelengths (colours) of a camera chip, you need to consider how this matches the response of the (average) human visual system. It will come as no surprise that cameras see light differently, but even so, we do have cameras that can capture images fairly accurately...
The manufacturers of the cameras and the software in them, go to great trouble manipulating the data in camera to produce a realistic image. The amount of manipulation varies whether you are saving raw or JPEG and upon various camera settings, but there is a lot going on that you have no knowledge or control of.
The problem of sensors not 'seeing' the same as our eyes is common to cameras and scanners.
With scanners you have an essentially constant known light source that you can build your input profile upon. Your profile enables you to apply a 'translation' that compensates for the characteristics of the scanner light source and sensors to give more or less accurate colour reproduction. The problem with a camera is that unless you are in a rigidly controlled studio environment, you don't really know what your lighting source is like.
In this article I'm going to look at how the Eye One match software allows you to build camera profiles for a particular situation, such as a product shoot in a studio. I'm also going to look at other ways that you can make use of the SG card to improve the colour accuracy of your work, both in the studio and on location.
Using Eye One Match to create profiles
The ColorChecker SG card is an 8.5x11 inch card with coloured patches on it. It happens to be a lot more sophisticated than the kind of paint colour chart that you get from the local DIY store, but it's basically the same sort of thing...
ColorChecker SG info (from GretagMacbeth)
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It's not a cheap bit of kit, so I keep mine in its original packaging in a cool dry cupboard when not in use. If you are using it regularly for extreme accuracy, GMB recommend replacing it every two years.
| The card is an expanded version of the original ColorChecker card which will be a familiar sight to many photographers.
If you look at the upper centre of the SG card you can see that all the colours of the original card are reproduced in their same relative positions -- a useful feature that I'll expand upon later. |
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The SG in the card name stands for Semi-Gloss and refers to the colour finish of the squares in the new card. The colours are supposed to be the 'same' as in the original, however several people have found small but significant differences.
The new card has a much wider range of colours than the original, which should lead to better quality profiles. The light grey under the green patch is the one I used for grey balancing images throughout this review.
The process of creating a profile is a deceptively simple one.
- Photograph the card,
- open up the image in the profiling software,
- create a profile.
The profiling software can cope with having the target slightly skewed, but for maximum profile quality it must be very evenly illuminated, and have no reflections. It's here that you discover that semi-gloss can pick up reflections from all over the place...
When you open Eye One Match you can select an 'Easy' or 'Advanced' mode for creating your profiles. I'll start with the 'Easy' mode
Easy Mode
Camera profiling
As ever with the Eye One Match software there is some very useful help available, in this case advising how to take a photo suitable for profile creation. As well as even lighting, you need to ensure that the white patches are between 230 and 245 (8 bit RGB values) and the black ones below 20. You do not have to fill the entire frame, since you will crop the target once loaded.
Picture Advice
The next bit is where there is some potential for confusion. You need to get an image in TIFF or JPEG format to analyse. A JPEG is pretty easy to get straight from the camera, but what if you are shooting RAW?
- Mar 2007 - I've just reviewed V4.2 of DxO Optics Pro for RAW conversion and image correction - it can directly output a tiff file from your RAW image, specifically for creating ICC camera profiles. These can then be used in its RAW conversion settings
I used Adobe Camera Raw 3.1 to convert my (raw Canon 1Ds) file at 16 bit into the large ProPhoto colour space. It is important that you note the conversion settings, since your profile will be based on the image that you supply. Your profile is going to be applied to the image later, so you can see that if you have changed something like the saturation in ACR for a subsequent image, then the profile won't be relevant.
I trust you can already see why this technique doesn't look too promising for photos taken under variable conditions - but as I'll show later it's not quite so bad.
Load the Image
The loaded image is then cropped to include just the coloured patches.
Cropping
A quick check to see that you've not got the image upside down :-)
Note the very odd colours -- I'm doing this test with fluorescent lighting, which I know is really difficult to get good results from.
Checking the chart
Now just let the software do its stuff, and save the profile wherever profiles live on your system.
Saving the Profile
Do give your profile a more meaningful name and be sure to write down all the relevant details about camera and lighting settings.
You now have a profile ...
Advanced Mode
Before I show the profile in use, I'll show the much more detailed 'Advanced' Mode
In this mode you specify the lighting that the profile is being constructed for, or you can measure the lighting with an Eye One spectrophotometer and make the profile for that particular light type.
Specifying lighting
As you can see, you are now tying your profiles to standardised light sources, so as long as the lighting you are using conforms to one of them, there is a chance for getting a slightly more portable profile.
If you are using this setup in a studio then I'm going to assume that you know your lighting well enough to be able to create a whole set of profiles for different lighting sets. Just how far you want to go along this road very much depends on the type of work you do and the requirements of your clients.
In advanced mode, the software is much more picky about getting the lighting of the target correct, and will warn you of problems. The easy mode does this too, but seems not to be so fussy.
In this case I'd not carried out a grey balance in my Camera Raw conversion.
Grey balance warning
After a profile is generated, you get the chance to fine tune it. You need to load a test image shot and processed under identical settings in order to alter the behaviour of the profile.
In this case I've used a shot that contains the image of the target that I've just used to create the profile -- I'd just cropped it out and used that to make the profile.
First you can change exposure and contrast settings. There are a number of ways the picture is presented for you to decide on any changes.
Then the saturation
and lastly the shadows and highlights
The profile is modified and your adjustment settings are displayed (for you to make a note of)
You can go back and repeat the process with further images, building up your profile collection at a rapid rate...
Saving a modified profile
So I've now got my profile. What do you do with them?
Using the profiles
In the workflow I've followed so far I've taken my pictures, converted the raw files in ACR, and saved them in the ProPhoto space. I've picked such a big space (at 16 bit) so as to capture as much of the information from the camera as possible. I normally work in Adobe98 or sRGB for web use, so I need to work the profile into my conversion to one of these spaces.
- Note that if you use a raw converter that directly supports camera profiles, the process of using them is a little more straightforward, however like many people, I don't use such converters in my daily work, so hence this slightly more convoluted approach.
First I assign the new profile to the image - it should look better. Then I convert it to my chosen destination space. Hopefully, I now have an image with more accurate colours in it.
Remember though that perfectly accurate colour may not look the most aesthetically pleasing, and if you are going to be printing the results, your 'all new improved' colours may not actually be printable by your chosen output device and media...
It's not easy to show examples of the difference that a profile makes, in articles on the web. The picture below was taken in a local all night convenience store that is very brightly lit with a range of fluorescent lighting types and fittings. It's been converted to an sRGB JPEG here.
The image shows some drinks bottles, which should be common enough that you know the colours wherever you are reading this article (OK perhaps not everywhere, but Coke bottles are pretty ubiquitous throughout the world)
- The picture initially shows a converted raw file, using what the camera thought was a reasonable grey balance.
- If you place your mouse pointer over the image, it will show a version after I have grey balanced it in ACR using the grey on the SG card.
- If you click on the image and hold down the mouse button then it will show the results of applying a custom profile - note in particular the changes in the 'Coke' red.
Applying a profile
I'll have some more examples later, but first I'm going to show how to use the SG card to calibrate Adobe Camera Raw itself
Calibrating Adobe Camera Raw
If you look at the calibration tab in the ACR window, you will see a whole host of adjustments that you can fiddle with to alter the colour conversion. Indeed you can even use them to fine tune the conversion of colour to black and white in ACR, although I prefer to do it after conversion when I can use specialist techniques in Photoshop (collection of conversion techniques)
| You can use these settings to correct colour conversion if you have an image of the ColorChecker card.
The difficulty is that the sliders all interact, so you change one and it affects the settings needed for another slider and so on. All very messy and whilst it may be an interesting exercise, I can't imagine doing it very often for real work... Bruce Fraser has written an excellent article explaining more about calibrating ACR. |
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Help is at hand in the form of a script by Thomas Fors that will automate the calibration process by repeatedly using ACR and comparing the results with the correct values for the coloured patches.
Info on the script is at his site http://fors.net/chromoholics/download/
The coloured patches you need, are shown in the middle of this picture of the SG card (which has been corrected in ACR)
Sounds great ... but hold on. Remember I said that the SG colours were not quite the same?
So you have your nice new SG card, and you can't use the script :-(
Since the source code for the script is available I had a look at it and found the bit where the patch data is stored. By measuring the actual values of patch data with my Eye One Pro, I was able to build up a table of the equivalent values for the SG card (a rather convoluted process that I'm not going to go into here)
The upshot of this is that I have a downloadable version of the script that will work with an SG card.
Some things to remember
- The script is Thomas Fors' work and Copyright ©2005 Thomas Fors.
- The SG values are those measured for my own card - I believe they should be OK for others but I have no idea about how accurate my measured values are (the card was only a month old and had not been used much at all).
- The script is based on Beta3.4 of the script - the values in my version should be applicable to past/future versions, but you will have to edit them yourself, if I've not posted a new version. This version is for CS2 and ACR 3.1
- Use the script exactly as described on Thomas Fors' site, with the exception of using an SG card rather than the original ColorChecker.
| From the modified script (RGB values in the ProPhoto space)
// Pro Photo RGB Reference |
The script (for CS2 and ACR3.1) is available as a zipped file.
- version supporting ACR 3.2 (Oct 05)
- version supporting ACR 3.3 (Mar 06)
I would really appreciate feedback from anyone using this modified script
The script takes over a half hour to run (can be greatly reduced if you set up ACR correctly) and produces a set of numbers that you use in ACR
I've saved the settings for quick application to images.
Not exactly a profile, but lets see how the various techniques for getting better colour compare
Better colour in your pictures?
The picture below shows the Coke bottles again (grey balanced ACR conversion), but this time if you move the mouse pointer over the image you will see the ACR corrected version, and if you click (and hold) you will see the Eye One Match generated profile version.
You'll note that the profiled version is also a little darker. On my calibrated monitor it looks noticeably better with a much more even rendition of the colours - what you are seeing is an sRGB compressed JPEG in a web browser - so your mileage may vary :-)
It's quite difficult to see in an sRGB JPEG, but the colours in the profiled version are better matched to the card.
A larger version...
Detail of previous picture (unsharpened)
I've not gone into the precise numerical accuracy of the profiles created, since it's the sort of stuff that if you know how to do it, then you'll already be making your own profiles, and this review is aimed more at those looking into camera calibration as an option to explore.
That said, if anyone wants more of the technical colour geek info, then just drop me an email :-)
Summary
Buying the i1
We make a specific point of not selling hardware, but if you found the info on our site of help, please consider buying an i1 (any version) via our link with Amazon.
It won't cost any more (nor less we're afraid) but will contribute towards the running costs of our site
The Eye One Match software is easy to use and has useful and appropriate help functionality.
The SG card can be tricky to light well, fortunately the software spots most lighting related problems, and will tell you if an image is not suitable for making a profile.
The easy profile generation is quick and simple, and in many situations would give a perfectly useful profile for a particular lighting set. The advanced mode offers many more adjustments which you might want to experiment with - the ability to profile for standard lights is useful if you know your lighting, although the ability to actually measure the lighting gives the ultimate in customisation.
The comparison images used in fine tuning in the advanced mode seemed a bit small and difficult to use. I'm not sure just how I'd personally use this feature in real use, since I'd do the adjustments in Photoshop. The more precise the kind of work you do, the more likely you are to find the range of features in advanced mode useful.
My test of going to the local brightly lit supermarket is probably not the kind of situation where you would carry out profiling. I was however very pleased with the results. I tested the software with raw and jpeg images taken with a Canon 1Ds and Olympus E20 - both worked fine.
Both the ACR calibration and Eye One Match profiles produced marked improvements in image quality in awkward lighting conditions. The ACR calibration could possibly be improved if you had the time to tweak the adjustments, but the Eye One Match profiles looked very good (do note that the optimization code in the ACR script can produce odd results sometimes).
The usefulness of camera profiling really depends on the type of work you do. For much of my own commercial work I'm not working in a studio, so the results I get with ACR or DxO for converting my raw files are more than good enough. I do now know that even if I'm in a nasty fluorescent lit room I have some additional tools for getting my colour right.
If you use a raw converter that directly supports camera profiles, then you might get even more consistant results from the profiles - however I don't use such converters in my daily work. Thus the work here to show what you can get using ACR (which is what a lot of people actually use).
If you don't need the full profiling package, then the original ColorChecker card with ACR may suffice, but if your work depends on colour accuracy then this package could soon repay its cost.
The ColorChecker SG and Eye One Match software is available from GretagMacbeth.
Special thanks to the SPAR store on Fosse Rd, Leicester for permission to take pictures late at night :-)
Interestingly enough, one customer spotted the SG card and knew why I was using it!
More Info
- Colour management links on this site
- Eye One scanner profiling - review
Using the Eye One with a scan target to get better results form your film or flatbed scanner. - The Spyder2 Pro - review
- The Eye one Display 2 - review
- Review of the printer profile editor in Eye One Match.
- Calibrating ACR - by Bruce Fraser
- http://www.brucelindbloom.com/ - has useful info on many colour related areas, including lots on the original ColorChecker
- http://www.rags-int-inc.com/PhotoTechStuff/MacbethReader/
More scripting fun with Photoshop and ColorChecker cards - it should be possible to include my SG card measurements into the script, although mine are only for ProPhoto. - http://www.colorremedies.com/realworldcolor/downloads.html
Useful resources - related to the 'Real World Color Management' book - http://www.babelcolor.com/main_level/ColorChecker.htm
Lots of ColorChecker related info
We have a version of Google's Search engine, optimised for photography related items that may be of use in finding more information...
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