Scanner Calibration

[aggibson74]

I just picked up an Epson V750 and I am investigating how to calibrate it. I understand that you have to use a transparency target like an IT8 target to give the calibration routine a known set of colors.

What I don't understand is why you would need need an IT8 target for Velvia and a different one for Provia. I know these films render color differently, but you would be calibrating the scanner and the film together with these targets.

I use velvia because I like the colors it gives me. Would I loose these colors with a velvia calibration target? Is there a neutral target which can be used just to calibrate the scanner? I want to see what I see on the light table.

Thanks,
Al

[Marc B.]

What software are you using?
Film emulsions are often reformulated every few years, and new targets are developed to match.
Were any targets supplied with your scanner?
The targets establish a profile for the films you will be scanning.

[aggibson74]

Thanks for your response Marc,

I was planning on using Vuescan, but that shouldn't matter for my question. I didn't get any targets with my scanner.

In order to calibrate just the scanner, I don't think it should matter what emulsion is used in the film. The emulsion should affect the color rendition of the film, but not the scanner.

If you are concerned with the emulsion that was used in the film, then you are trying to calibrate both the scanner and the emulsion.

For example. If you take a picture of a red barn with astia, the color of the slide will look different than the same red barn taken with velvia under the same lighting conditions. If you were to put the two slides side by side on a light table, you will see they are different. If you were to use the appropriate astia and velvia scanner profiles, would the color of the red barn still look different after the scan? I would assume they would look the same since the scanner profiles took into consideration the way each film rendered the color.

However, I don't want them to look the same. In some situations I like the velvia look and choose to shoot that film for the look. In other situations I like the astia look and choose to shoot that film.

Is there a 'generic' IT8 transparency available that will just allow me to compensate for the color rendition of the scanner?

Thanks,
Al

[Preston]

I was planning on using Vuescan, but that shouldn't matter for my question.

Actually, telling us what scanner software you use can help us to answer your question(s)


The emulsion should affect the color rendition of the film, but not the scanner.

This is true, but if the emulsion is changed, certain characteristics of the film will be different; thus the need for an updated IT8 target and look up tables.


Is there a 'generic' IT8 transparency available that will just allow me to compensate for the color rendition of the scanner?

The profiles made by Epson for your scanner are 'generic'. If you want the output of the scanner to match as closely as possible the color rendition of the original, then you'll need to calibrate using the IT8 target for that particular film. If this were not the case, then why would manufacturer's create IT8 targets for specific films?

I will note that my Microtek 1800f is not IT8 profiled. I use the 'generic' profiles and scan so that my output images are fairly flat. They get me close enough so that adjustments in Photo Shop are relatively straightforward.

--P

[aggibson74]

Thank you for your response Preston,

By 'generic' IT8 transparency i didn't mean the canned profile from Epson. I was trying to describe a piece of film with known colors that wasn't emulsion dependent. I can use this transparency to adjust for the way my specific scanner looks at colors. The canned profiles from Epson don't take into consideration my specific scanner and is an average value for their manufacturing run of scanners.

Maybe another way to look at the question is to think of having 2 different slides of different emulsions that show the same color on a light table. In this case the two real world objects used to create the slides would be of different colors, but due to the emulsions, ended up looking the same on the light table. I want my scanned image of each slide to look the same as it did on the light table, not the real world object. I would think only one profile would be needed to accomplish this, since I don't care about the emulsion and the real world color of the object.

To answer :
"If this were not the case, then why would manufacturer's create IT8 targets for specific films?"

Perhaps the manufactures are trying to remove some of the color cast of the film so that scans are more representative of the real world object and not the light table.

The reason I want to know this is that I like to have a full understanding of my workflow and its limitations. It also helps me know where to look in my workflow if I'm not getting the results I expected.

Thanks,
Al

[Mark Stahlke]

...but you would be calibrating the scanner and the film together with these targets.You want to profile the scanner and the film together just as you profile your printer and paper together.


I use velvia because I like the colors it gives me. Would I loose these colors with a velvia calibration target?No, you would not.


I want to see what I see on the light table.That's the whole point of calibrating your scanner, isn't it?


If you take a picture of a red barn with astia, the color of the slide will look different than the same red barn taken with velvia under the same lighting conditions. If you were to put the two slides side by side on a light table, you will see they are different. If you were to use the appropriate astia and velvia scanner profiles, would the color of the red barn still look different after the scan? Yes, of course.


I would assume they would look the same since the scanner profiles took into consideration the way each film rendered the color. No, not at all.

The good news is that the differences in emulsions are not that great. I created a profile for Velvia 50 on my Epson 4990. It works flawlessly with Velvia. It also works fairly well with other films like E100VS. Someday I'll get a target for Ektachrome films and create a proper profile for them but until then my Velvia profile is close enough. And much better than no profile at all.

By the way, I recommend IT8.7 targets from Wolf Faust. (http://www.targets.coloraid.de/)

[Peter De Smidt]

By the way, I recommend IT8.7 targets from Wolf Faust. (http://www.targets.coloraid.de/)

+1. They're not that expensive, and they are very effective. Using the right emulsion does make a big difference, as you can see by the various profiles that are made with the different targets.

[neil poulsen]

I tried using the Hutchcolor Velvia target to develop a profile for Ektachrome. It didn't work that well.

Reading on the Hutchcolor site, he describes a process to make this work. But, it requires a viewer with a variable ballast. Quite expensive. See page 15 (Pseudo Profiles) in the following document.

http://www.hutchcolor.com/PDF/User_Guide.pdf

Another good link is his Scanning-Guide.

http://www.hutchcolor.com/PDF/Scanning_Guide.pdf

I didn't following through on the Pseudo Profiles, because at that time, I didn't have the Soft-View.

[aggibson74]

I found something that tells me why the emulsions of the it8 profile matter. It has to do with the response of the scanner to the film itself, not the way the film renders the colors.

Here's a link:
http://www.computer-darkroom.com/it8cal/it8_page_1.htm

But here's the part of that document that describes why:
Another area of scanner profiling that causes confusion is that of the film characteristics. Many folk are of the view that because each film will tend to have a different colour bias then we need to build a profile for that type of the film. However, whilst images will tend to vary from shot to shot depending upon exposure and ambient lighting the film's colour bias will within certain limits (the exception being reciprocity law failure with long exposures) remain fairly constant. So in effect it's not the film that we're profiling, but the scanner response to it. Again, the technical information provided by Kodak has the following to say on this matter:

"It is important to note that any colour photographic product contains both image capture (sensitizing) dyes as well as image-forming dyes. While the image sensitizing dyes are a vital part of the film performance, it is only the image forming dyes that affect scanner calibration or characterisation. Fortunately, only a small number of image forming dyes are used. Specifically, one set of image forming dyes can be used for EKTACHROME film, and one for EKTACOLOR paper. This means that only one Q-60 target is required to represent the complete EKTACHROME film family and one for EKTACOLOR paper"

Nevertheless, when I set about this comparison of IT8's the jury was still out on whether we should always match a Fuji target to Fuji films and a Kodak Ektachrome target with Kodak Ektachrome films, etc. To be honest I've not yet come across a real world situation where scanning an image captured on Fuji film whilst using an ICC profile based on a Kodak Ektachrome target has caused me any great problems; at least not for anything other than precise colour matching. However, the same cannot be said of Kodachrome type film as it really does require a matched IT8 target. Likewise it's very likely that we'll need different targets for Velvia RVP 50 and the new Velvia 100F as these two films are in many respects very different from each other and the rest of the Fuji range.

-Al

[Ken Allen]

It's a matter of precision. How precisely are you trying to replicate an object/color with a different means of generating and viewing that object/color.
Calibrating your scanner with any target will improve your color management system over not calibrating. And calibrating your scanner with the exact type of object/color that you are using will reduce variables an improve your precision.
So it's a process of elimination variables to improve accuracy, and some variables are not easily controlled.

[SteveH]

I don't mean to hijack this thread :o but the other side of scanner calibration is focus calibration.
I would be interested to know how many people have used a USAF1951 target or similar to find the optimum focus of their scanners and how useful you found this to be.
Considering that a USAF1951 target is about US$100 on glass plate, is it worth the investment? I know Sandy King has posted results of test of his scanner.
What other options exist?
Thanks
Steve

[Ken Allen]

When we use the digital copy stand we use reflective and transmissive resolution charts and they are important to the quality control process. But the Epson 700/750 scanner is a set 2-step set focus (no auto focus like the 10,000), so I don't believe that can be calibrated? Or am I wrong? I only tested this scanner, and do not have one.

[SteveH]

Hi Ken
the V700/750 is calibrated by adjusting the height of the film holder. The Epson holders are a 3 step adjustment, the better scanning holders have a continously variable height adjustment.

Steve