Digital BW, The Print

Steve,

>...A normalized pixel value of 0.5 equates to a density of 0.6623 ...

OK, then that is consistent with the average comment being that the prints are a bit lighter than the monitor image.

>...Carl Schofield previously provided the following formula 
>for calculating density from LAB's L value.

>If L>8 then Y = ((L+16)/116)^3

>Else Y = (L*27)/24389

>And Density = -Log10(Y)

>With L = 54 this would yield a density of 0.6581

>To be honest I have no idea why the two formulas end up with a different
>value...

>...
>Actually, what does one of your curves do at norm PV = 0.5 in order to get
>the 50% step = 0.61 density?  Is it shifted at all?   (128 or 50% if your
>prefer

Most of the curves require that a grayscale file be converted to Adobe RGB first.  Then the RGB curves map to the CMY inks, black being generated by a combination of the curves.  So, the RGB curves provide input-output relationships that allow me to specify the density of the image at each point.  It's just using Photoshop curves and the driver controls or built-in characteristics (including cross-overs) to do most of what RIPs do.

>...
>Ansel defined mid grey at 18% reflectance, ...

My Kodak standard gray, which I believe is 18% reflectance, reads as Lab L=50 with my X-Rite.  That is more like 0.73 density.

So, bottom line, what I'm hearing is that 0.66 might be closer to the mark as far as a standard midpoint density for the final print.

I generally like the idea of having a standard midpoint as opposed to cutting the total range in half.  I think the standard midpoint makes it easier to print the same image on different papers without having to re-do the file.

Interesting stuff, but it's too easy to get hung up in the numbers and ignore the aesthetics of the image.

Paul
www.PaulRoark.com 

__________________



> From: Steve Kale <stevekale@btinternet.com>
> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Date: Fri, 03 Dec 2004 17:21:24 +0000
> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
> Subject: Re: [Digital BW] Tonal range and linearization
> 
> 
> Sorry, is this meant to be a subjective empirical test? Ie which do I
> subjectively prefer?
> 
> I use a workspace of Gray Gamma 2.2.  Someone who knows the intricacies of
> this space better than I may correct me, but I would say that if:
> 
> Luminance = C * value^gamma + black level
> 
> (taken from Norman Koren's site)
> 
> And we can usefully set C and black level to 1 and 0 respectively, then a
> normalised pixel value will have a luminance of 0.2176. If
> 
> Density = - log10(luminance)
> 
> Then it will have a density of -0.61.  Given it is a reflected density this
> then is 0.61.  That is, to match the workspace I would say it should print
> with a density of 0.61.
> 
> I thought I had read somewhere that PS uses LAB as the intermediate colour
> space when converting from one space to another.  I also thought LAB had a
> gamma of 2.2.  Perhaps I am wrong on this.
> 
>> From: Paul Roark <paul.roark@...>
>> Reply-To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
>> Date: Fri, 3 Dec 2004 08:51:49 -0800
>> To: <DigitalBlackandWhiteThePrint@yahoogroups.com>
>> Subject: RE: [Digital BW] Tonal range and linearization
>> 
>> 
>> Steve,
>> 
>>> Yes you are right because you in effect manually set the 50% grey slot
>>> (presumably with some iteration).  My comment was made in relation to a
>>> programme such as QTR where the midpoint is a function of linearization...
>> 
>> Yes, it is an iterative process.  The driver is a bit of a black box, but
>> once one gets used to it, it's quite predictable.
>> 
>> But, back to the simple question, would L=50 be a better midpoint?  If you
>> print a 21-step test strip, like one at
>> http://home1.gte.net/res09aij/Test-files.htm, would it match the monitor
>> better if the midpoint were more like density 0.73 (a bit lighter than the
>> current 60%) than the current 50% = 0.61?
>> 
>> Paul
>> www.PaulRoark.com
>> 
>> 
>> 
>> 
>> 
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BY PARTICIPATING IN AND/OR POSTING MESSAGES TO THE DIGITAL BW, THE PRINT YAHOO! GROUP YOU EXPRESSLY UNDERSTAND AND AGREE THAT THE OWNER AND MODERATORS OF DIGITAL BW, THE PRINT YAHOO GROUP SHALL NOT BE LIABLE TO YOU FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, CONSEQUENTIAL OR EXEMPLARY DAMAGES, INCLUDING BUT NOT LIMITED TO, DAMAGES FOR LOSS OF PROFITS, GOODWILL, USE, DATA OR OTHER INTANGIBLE LOSSES (EVEN IF THE  OWNER AND MODERATORS OF DIGITAL BW, THE PRINT YAHOO GROUP HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES), RESULTING FROM: (i) THE USE OR THE INABILITY TO USE THE DIGITAL BW, THE PRINT YAHOO GROUP; (ii) UNAUTHORIZED ACCESS TO OR ALTERATION OF YOUR TRANSMISSIONS OR DATA; (iii) STATEMENTS OR CONDUCT OF ANY THIRD PARTY ON THE DIGITAL BW, THE PRINT YAHOO GROUP; OR (iv) ANY OTHER MATTER RELATING TO THE DIGITAL BW, THE PRINT YAHOO GROUP.
 
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