Re: CompassProfile - help creating greyscale profile for RGB device.
Re: CompassProfile - help creating greyscale profile for RGB device.
- Subject: Re: CompassProfile - help creating greyscale profile for RGB device.
- From: "Reed Photo-Imaging" <email@hidden>
- Date: Wed, 9 Apr 2003 10:55:20 -0600
>
There are two possibilities here that can be confused with one another. If
you build a color profile for grayscale uses, it will attempt to blend colors
effectively to create neutral grays. This is fine for printing grayscale
iamges with color processes, but unrelated to printing with grays only.
Yes, and we do both here, print chromogenic black and white as well as silver
based true black and white.
>
For printing true grays only, a three dimensional Look Up Table is not
applicable, all you need is a two dimensional curve correction ofr your one
channel. You can build one of those in Photoshop's custom CMYK setup's custom
black dot gain window, and save it out as a CMYK profile, if your application
will then use the black curve from that profile effectively to print B&W
images, or you could build one in the standard curves window in Photoshop from
a 16 patch gray ramp and correction points to match in Photoshop, and then use
an action to apply that curve to all your images before printing.
This would certainly work for us and our clients, but only within certain
areas of workflow.
There are several reasons that a user may prefer a profile over that of a
curve. If my sole purpose was strictly for in-house use in the preflight
stages, I would agree that the curve is satisfactory. Unfortunatly my original
post did not include enough detail regarding potential workflows, and I
appologize for my brevity.
A good greyscale profile can be used for generating excelent greyscale images
from color files, that exhibit accurate perceptual representations of
luminosity. Photoshop is not linear in this area of conversion. Their
alogorythm is biased heavly towards the red, and although the attempt is a
valiant one. It is not accurate. Placeing a white, or black layer above the
image, and set to saturation mode, gets closer, but is still not perfect.
Using the Luminosty channel in LAB mode is the closest I have seen, but still
does not quite get us there.
I do get "acceptable" results from the lab method, and sometimes it requires
blending the LAB technique with the white layer to get where it needs to be. A
custom grey colorspace on photoshop may be the answer, but the hours required
are daunting and better spent elsewere. If it comes down to being my last
resort, I am willing to spend the time to improve the product and the clients
workflows.
Other areas of use might be with the client attempting to proof using inks,
quad or otherwise. As well as inhouse matching of our Giclee prints to our
LightJet prints. To the best of my knowledge, this is best doen with profiles,
and the additional "tweaking" inevitably needed to zero in the product.
John Harris
Digital Division
Reed Photo-Imaging
303.573.8084
800.999.8084
http://reedphoto.com
----- Original Message -----
From: email@hidden
To: email@hidden ; email@hidden
Sent: Wednesday, April 09, 2003 10:08 AM
Subject: Re: CompassProfile - help creating greyscale profile for RGB
device.
In a message dated 4/8/03 8:12:39 PM, email@hidden writes:
We are attempting to generate a greyscale profile for our LightJet
printers.
These are photographic printers using RGB lasers to expose photographic
emulsions. We print both chromogenic and real black and white materials.
Here
is the rub: Although there are several workarounds for creating grey
swatches,
the software refuses to recognize the need to evaluate them as grey, so
the
resulting profiles attempt to force color back into the image file. This
results in extreme color posterization, and any hope of tonal integrity
is
lost.
There are two possibilities here that can be confused with one another. If
you build a color profile for grayscale uses, it will attempt to blend colors
effectively to create neutral grays. This is fine for printing grayscale
iamges with color processes, but unrelated to printing with grays only.
For printing true grays only, a three dimensional Look Up Table is not
applicable, all you need is a two dimensional curve correction ofr your one
channel. You can build one of those in Photoshop's custom CMYK setup's custom
black dot gain window, and save it out as a CMYK profile, if your application
will then use the black curve from that profile effectively to print B&W
images, or you could build one in the standard curves window in Photoshop from
a 16 patch gray ramp and correction points to match in Photoshop, and then use
an action to apply that curve to all your images before printing.
C. David Tobie
Design Cooperative
email@hidden
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