[argyllcms] Re: Profiling backlit film (with Monitor?)

  • From: Alexey Gribunin <Gribunin@xxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 1 Dec 2017 20:07:20 +0300

Hello Roger!

1. Chartread. I'm measuring with Chartread –t. I prefer it because the i1Pro calibration is performing relative to lightbox+clear backlit. So the testform's paper patch (CMYK 0000) is L=100, a=0, b=0, i.e. perfect white and it's not necessary to recalculate it afterwords.

2. Strip mode vs Patch mode. Theoretically Strip mode is possible but in my practice it's very unstable because the light intensity of lightbox is not enough. Maybe it's possible to do with higher intensity lightbox, but it seems to me that then another problem will arise - i1Pro drift due to overheating.
So I'm using patch mode. It's slow but it's stable.

3. lightbox. Theoretically an incandescent light source with 80A (or similar) blue filter would be very good choice. I tried to construct lightspot for patch measurements with incandescent light source and 80A filter. CRI of such construction is very good, the spectra is similar to real D50. But I found that overheating also is an issue. The spectra of such construction still has quite high amount of IR. So it's better to add an IR filter also. But I didn't find it and left this idea for simpler light sources...
In my practice iPad (i.e. LED source) showed himself better than fluorescent light source. It's more stable and it's also much more usable because I always have it in my bag :))))

So I would suggest you to try LED first to develop the complete workflow and then to think about another types of lightboxes.

Best regards,
Alexey Gribunin, UNIT Color Technologies, Moscow, Russia.

On 01/12/2017 19:32, Roger Breton wrote:

All of a sudden, I need to come up with an ICC profile for backlit media – small world!

Many questions…

First, suppose I use Chartread –e. Can I read in strips with the i1pro? Or do I need to read in Patch mode?

Second, choice of lightbox. Is it “better” to measure with the media sitting on a fluorescent light source? Or is it better to measure with an incandescent  light source? Why not  LED light source?

I was thinking of using this kind of lightbox:

https://www.ebay.com/itm/1x-JUST-Normlicht-Color-Smart-Light-5000-Transparency-Flat-Viewer-15-x-10/361307134398?hash=item541f9559be:g:LtkAAOSwNSxVZhQt

I remember reading that the issue of light source “color temperature” was not important. How is that?

Best / Roger

*From:*argyllcms-bounce@xxxxxxxxxxxxx [mailto:argyllcms-bounce@xxxxxxxxxxxxx] *On Behalf Of *Kamil Tresnak
*Sent:* Thursday, November 23, 2017 5:22 PM
*To:* argyllcms@xxxxxxxxxxxxx
*Subject:* [argyllcms] Re: Profiling backlit film with Monitor

Thanks for sharing, Alexey!

Regards,

Kamil Tresnak

    In the past I used LCD monitor without matrix (it was damaged, but
    lamp itself was good, so I just remove the matrix and used it as a
    light table). But the uniformity and stability is not very good, so
    it was necessary to calibrate i1Pro every few patches.

    Now I'm using iPad (!) and found it much more stable
    (auto-brightness=off).

    But calibration every 10-15 patches is also highly desirable. It's
    necessary to get really repeatable and reliable values.
    I'm calibrating device during measurements in two different ways:
    1. I'm making ArgyllCMS native calibration every 75 patches.
    2. I'm measuring white patch every 15 patches and making linear
    spectral correction afterwords in EXCEL.

    Best regards,
    Alexey Gribunin, UNIT Color Technologies, Moscow, Russia.


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