Creating Lab image files from Lab data files
Creating Lab image files from Lab data files
- Subject: Creating Lab image files from Lab data files
- From: Marco Ugolini <email@hidden>
- Date: Sun, 26 Jun 2005 21:22:10 -0700
In a message dated Mon, 13 Jun 2005 12:42:38, Bruce Fraser wrote:
> There's a bug in the current versions of ColorLab that causes Lab
> TIFFs generated from data files to be screwed up in an interesting
> way. On both the a* and b* channels, the sign is reversed, and the
> values from 0 to 128 are flipped.
>
> I suspect that someone much more skilled in Excel than I am could
> write a formula that would munge the Lab data in such a way that the
> TIFFs came out right. I'm sufficiently math-challenged that it made
> my head hurt thinking about it.
Bruce,
I have good news. I know a workaround that fixes this bug in ColorLab.
I put my mind to it, and I found out how to create accurate image files in
Lab mode from Lab data values in ColorLab. It's so simple, in a sort of
backward way, that I should have figured it out earlier. And there is no
need for any Excel wizardry either.
1) Start out from a data file listing Lab values, one from which you wish to
create a Lab image file.
2) Open this data (text) file in ColorLab.
3) Choose "Export..." from the File menu. Choose "TIFF Images" from the
"Format" pull-down menu in the Save dialog box. Make sure that the file name
ends in ".tif". Click "Save".
4) This is where ColorLab screws it up. Open this TIFF Lab file in ColorLab,
and you will see that it looks all wrong. But ignore that. Instead, select
the "Filter" menu: choose Conversion -> Spot Colors...
5) Click the "Enable" check box, which will figure out for you how many
patches across and down are in your chart. Click OK.
6) Again, choose "Export..." from the File menu. This time choose "Text
files" from the "Format" pull-down menu in the Save dialog box. Make sure
that the file name ends in ".txt". Click "Save".
7) Open this latest text file in ColorLab. One last time, choose "Export..."
from the File menu. Choose "TIFF Images" from the "Format" pull-down menu in
the Save dialog box. Make sure that the file name ends in ".tif". Click
"Save".
8) Open this image file, and you will see that the values for all its
patches correctly reflect those in the original data file for each patch.
This is the final, and CORRECT, Lab image file that ColorLab should have
generated the first time around, but didn't.
So, basically, one has to force ColorLab to go around twice before it
surrenders the Lab image file that carries the correct values.
Pheew!
I'm sure that there is a way to do this using Excel too. But I would think
that this is a simpler procedure than that, since it involves only one
application, has relatively few and easy steps, and it's way friendlier for
the math-challenged (of which I am one too).
Yet, I would be delighted if someone could share an EVEN SIMPLER way to do
this (i.e., creating Lab image files from Lab data files). Suggestions would
be very welcome.
--------------
Marco Ugolini
Mill Valley, CA
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