Printer Calibration Option

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BobF
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Printer Calibration Option

Postby BobF » Sat May 31, 2008 2:22 am

Having bought the Printer Calibration upgrade, some questions have arisen in working through using it. As usual with LS, the documentation is less than adequate.

1. Most printer profiling solutions give you the option to tweak the profile once it's created. Typically a profile may need to be adjusted for contrast or saturation slightly. Is there a way to do this with the PC module in SF?
2. Following up on the first question, profiles created with the PC module have reasonably accurate colours but there is a fairly marked drop in contrast and a slight drop in saturation. I've compared the profile created with SF to a profile provided by a paper manufacturer and the contrast and saturation differences are quite evident. Any explanation or solution?
3. Is a low rez prescan; which is what the PC module uses, sufficient to get accurate colour and contrast? It seems it may not be.
4. Does it make a difference whether 48 bit or 24 bit mode is used? Or whether Auto Sharpen is turned on or off?
5. Is the scanner ICC profile created during the IT8 calibration used automatically to correct for errors in the scanner's reading of colour?

degrub
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Postby degrub » Sat May 31, 2008 3:42 am

Just some quick thoughts on your questions:


2. Following up on the first question, profiles created with the PC module have reasonably accurate colours but there is a fairly marked drop in contrast and a slight drop in saturation. I've compared the profile created with SF to a profile provided by a paper manufacturer and the contrast and saturation differences are quite evident. Any explanation or solution?

IF you are not using a spectrophotometer, you will not get the same results as the paper manufacturer's profile. WHat you are seeing is probably due to how the scanner sees the ink on the paper versus how it sees an IT8 target ( the reflectance will likely not be the same)
Also, how long did you allow the ink from the print to dry ? many inkjet prints are not stabilized for several hours to a day.

3. Is a low rez prescan; which is what the PC module uses, sufficient to get accurate colour and contrast? It seems it may not be.

SHould be. The IT8 scans for profiling a scanner are only around 2-300ppi if i remember correctly.

4. Does it make a difference whether 48 bit or 24 bit mode is used? Or whether Auto Sharpen is turned on or off?

24 bit should be adequate. No need for sharpening. Usually profiling routines ignore all settings and use their own .

5. Is the scanner ICC profile created during the IT8 calibration used automatically to correct for errors in the scanner's reading of colour?

yes, if it is applied. Otherwise a default for that scanner type would have to be used.

davidl3541
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Printer Profiling

Postby davidl3541 » Sat May 31, 2008 7:53 am

Profiling with a scanner:

"IF you are not using a spectrophotometer, you will not get the same results as the paper manufacturer's profile. WHat you are seeing is probably due to how the scanner sees the ink on the paper versus how it sees an IT8 target ( the reflectance will likely not be the same)"

That is a true statement; however, because of even slight differences between scanners it becomes even more important to be able to edit profiles.

I notice in comparing my Printfix Pro (Datacolor spectrophotometer) to the SF printer profile that there is a slight magenta cast when printing with my HP 8750. This is most visible in gray scales and portraits on my test images. It is a simple matter to remove the color cast with an edit process. Unfortunately, SF does not provide any means to perform even a simple edit.

For your information the IT-8 calibration has a factor of 1.4.

The bottom line is that the SF profile is pretty good; but could be excellent with the addition of a profile editor. Unfortunately the profile produced by SF for Black & White printing might not be good enough.

BobF
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Postby BobF » Sat May 31, 2008 1:31 pm

I understand and expect that there will be a difference between a profile created with a spectro and a profile created with a scanner. Given improvements in scanners since Monaco offered their scanner-based profiling option several years ago and the quality of the SF software I would have expected a closer match than what I'm getting.

As far as how long the prints have been left to dry, to this point I've only tried profiling some heavy, matte papers which dry fairly quickly. As an experiment, I created the first profile within minutes of the papers coming out of the printer (an Epson 3800) then again 8 hours later and again 16 hours later - no difference. There is a very, very minute difference between the latter two and the first but it is so small as to be imperceptible in the prints when viewed side by side at normal distances. The 8 hour and 16 hour profiles are identical.

As I said, the colours are reasonably accurate if a bit washed out (lowered contrast). Greens are a tiny bit yellow. I haven't tried any b&w prints yet but if the SF profiles print with a colour cast then they're not at all accurate. I'll do some b&w testing later today. And while, yes, it is possible to make editing adjustments to correct for these issues to some extent, it's difficult to correct 100% with additional adjustment layers if the actual profile can't be tweaked. On top of that, with an accurate profile, you shouldn't have to make those kinds of adjustments.

As far as the reflectance difference between the target and the paper, that shouldn't matter. And I'm using a transmissive target for my IT8 calibration which also shouldn't matter.

All in all, based on what I'm seeing so far, it looks like $100 wasted.

LSI_Muenier
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Postby LSI_Muenier » Mon Jun 02, 2008 2:51 pm

Dear Bob,

I agree in the replies written by degrub (thank you for that!).
The measurement process is totally internal and is not influenced by your scan choices (like 24/48 bit, Auto-Sharpen on or off etc.). In fact it is done using the full 48 bit color signal from the scanner, and the resolution is sufficient, too.

IT8-calibration must be done in reflective mode when it shall be effective for measuring the printed chart, as the generated ICC profile charactizes the whole light path (from the light source to the CCD) in the scanner.

There is really a difference between scanner measurement and spectral measurement (like costly tools offer). A scanner has only three color values for each color, whereas a spectro-photometer "sees" a color in lot more spectral bands. But nevertheless, using the IT8-calibration with the scanners, they have proven to generate so good measurements, that adequate printer ICC profiles can be produced.

Best regards,
Martin


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