25. October 2002
Scanner profiling on a budget 1/2
When setting up your digital darkroom you've spend a fortune on the computer equipment, on a printer, on a digital camera and perhaps also on a scanner.
But when using your scanner you realize that managing colors - getting the correct colors onto your screen and printer - is quite a challenge. In some cases even impossible. You've read about color management and scanner profiling, but it's expensive. The software is expensive and the color targets are expensive, so you stay with the possibility your scanner driver is offering.
This article, however, will show that there are ways of making custom scanner profiles on a budget, not totally for free but at least very cheap, that will bring you correct colors from your transparencies.
Read on.
Color management
If you are familiar with the concepts of color management and profiles then move on to the next section otherwise read some of the background here.
Every device you use in your digital darkroom that deals with color has it's own way of interpreting them; your scanner "sees" colors in a certain way, your monitor presents them in certain way and your printer prints them in a certain way.
This means that when scanning a say red color from your transparency in the scanner that red color is perhaps interpreted slightly different by the CCD than your eyes sees it.
When the image is then presented on the monitor it also has it's own way of showing a red color and therefore it shifts a little bit again and finally when printing the red color it will again be changed a little bit because the printer will make it's own interpretation of that color and mix the inks to what it think it should look like.
The final result may or may not be close to the colors you see on the transparency (or in the real world). If they are not close to your transparency there are a number of things you can do.
"Tweaking"
The obvious thing to start out with is to try to "tweak" the colors using an image manipulation software like perhaps Photoshop or other tools that maybe came with your scanner.
You can also make changes in your scanner driver which is likely to offer you a number of color adjustments tools and of course you have similar tools in your printer driver that will let you manipulate how the colors are printed.
The problem with this approach is that there are so many buttons and dials giving you a large number of variables that can be changed. If you eventually end up with a good setting you might realize that this setting was only good for one picture or perhaps for one kind of pictures.
Color tweaking should ideally be something you do with the image to give it your personal artistic style and not something that you do just to get correct colors.
Profiles
This is where profiling comes in to play.
A so-called profile is a small file that tells you (your image software) exactly how your scanner CCD "sees" colors. You can of course also have a profile for your monitor and a profile for your printer.
A program like Photoshop will use a scanner profile to "mathematically tweak" the colors of your scan into correct colors. It will also use a monitor profile to automatically change the colors to match your display and finally it will use a printer profile to make sure the colors on the printer are correct.
A profile for a "color" device is therefore a "lookup table" in which a color managed image manipulations software can lookup the correct color of say red and therefore convert the color to the correct red.
You can say that each device has it's own color space and that a profile is a "map" of that space.
This and the following part 2 of this article will show you exactly how you can create a profile for your scanner. Profiling your monitor and printer is beyond the scope of this particular article.
sRGB
Why do all color devices see or present colors in their own way? Why not make sure that they all produces compatible colors?
Well, this is where the color space called sRGB comes in. This color space is a standard defined especially to be used on the Internet, but also for many other applications.
The idea is of course to make a standard that all color devices can use to make them colorwise compatible.
Your scanner driver is likely to have a switch for the sRGB color space and so is your printer driver.
In a non-color managed image software you'd be forced to or at least you'd be better off using the sRGB color space.
So setting you scanner to output in sRGB and setting you printer to also output in sRGB will give you predictable colors.
Then why not just use sRGB?
Well, the sRGB color space is limited in its gamut. This means that the "amount" of colors that can be presented is limited. Your scanner is likely to be capable of scanning a much wider range of colors and likewise with your printer.
Should you someday want to extract even more details from shadows etc. in your scans, then you still need a custom profile for your scanner.
Besides it might also be, that the colors you get from the sRGB mode of your scanner isn't actually the colors you see on your slides. At least this is the case for my scanner; using the sRGB setting doesn't give me exactly correct colors.
Other reading
This was just a very brief introduction to color management and profiles. I will therefore urge you to read more about the subject on the Internet.
The very best explanation I know of is made by Mr.Jonathan Sachs, president of the Digital Light and Color company, can be found here.
I will warmly recommend you to read this article and after that you know all you need to know about color management!
How a scanner work
In your scanner driver you will be able to change a lot of settings. Some affects what we will call "analogue" settings and some are "digital" settings.
The analogue settings includes: Crop, Focus, CCD exposure time, Brightness of lamp (analogue gain) (and perhaps to some extend also ICE3 which uses hardware facilities to reduce dust and scratches).
The digital settings includes: Levels and gamma control, Brightness and Contrast, Sharpness, color balance and more.
While the analogue settings affects what is outputted from the hardware itself, the digital settings are all "just" post-scan image manipulation.
It is likely that your scanner hasn't got all the analogue setting possibilities. My Epson 1640SU photo flatbed scanner will only let you adjust the crop, while my Minolta Dimage Scan Multi Pro will let you adjust the Crop and the Focus.
You can therefore to some extend say, that your scanner can only scan in ONE way. The CCD will to some extend always produce the same image and everything else is post scan processing. Keep this in mind when you set up your scanner for profiling.
If you never want to go back to a transparency and re-scan it you should set up your scanner driver in a manner that is as little "destructive" to the original image as possible and that uses the scanners hardware in an optimal way. Therefore I recommend that you turn of all kind of digital settings including any kind of color management when you make your profile and when you make your scans afterward.
More on his later.
You can also read about this subject here.
Making your own scanner profiles
- the color targets
Before going into details let's recap why we want to make a scanner profile:
• The colors we get form the scanner isn't the colors we see on the transparency.
• Using the sRGB switch in the driver is not an option, either because we see a limited color gamut or perhaps even more likely because the colors still aren't exactly correct (this happens!).
• We want to make a "neutral" and optimal scan so that we only have to scan once. Your profile when then afterwards give us the colors we want.
• Even if we are NOT using color managed image software we still want to achieve correct colors (more on this later).
We are going to need a Color target and some profiling software or profile generating software.
In this article I'll describe what a color target is and where you can buy it cheap and in the next article I'll describe what software to use.
Color targets
A color target is a slide or a print filled with well-defined color patches.
Accompanying the color target is a small file precisely describing the colors of the target for the software to use when making the profile.
The color target we are using is going under the name Q-60 or IT 8.7.
Here are some examples of what they look like:
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Kodak reflective target
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Agfa transparency target
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These targets are often very expensive depending on how precise they are. If they are individually measured for the describing file, they are very expensive.
However, we can not profile without them, so your task here can not be absolutely for free.
A German company called Wolf Faust are making cheap print and transparency targets which I have had great success using.
I bought the package called "All You Need" special. It includes two transparency targets, one for Fuji films and one for Kodak films, and a printed target to be used for profiling a flatbed scanner.
Here is what I got for $60 excluding shipping:
(The file describing the printed target can be downloaded from the web site.)
Next article
In the next article I'll show you where to find free software for making profiles and how to use it, so stay tuned for more information about how to make custom scanner profiles.
[Update 31.10.02]
The second half of this article is now online.
Links
• Scanner Profiling 2/2 The second half of this article.
• Digital Light and Color "Serious Software for Serious Photographers". Good, low priced imaging software. Documents on many subjects, including color management.
• Wolf Faust Cheap IT 8.7 (ISO 12641) Scanner Color Calibration Targets.
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