On Jan 13, 2020, at 10:21 AM, Brown, James William wrote:
I will be doing film response curves exposed to a 21 step wedge
I found that unless I divided Y by 100, I had negative numbers.
if you shoot film and print digitally
and processed at various development times. I will do a linear scan of the
processed film and use https://imagej.nih.gov/ij/ to derive transmission ;
density readings.
I will scan my photographic negatives and print digitally on my Canon
printer. I am reading Beyond the Zone System by Phil Davis. He plots a curve
of printing paper such that the negative processing can fit to the paper
response.
I needed to have a method of reading reflection density reading so that I
could plot curves of various papers. There should not be a difference in this
process printing digitally or with wet chemistry.
I found that unless I divided Y by 100, I had negative numbers.
So that’s where I am headed-- shoot film, print digitally.
I have high end digital camera gear. I am just having nostalgia for the days
of my youth.
I am probably being over precise. Using Photoshop adjustments, I can probably
make most any negative print well. Proper testing just makes it easier.
I appreciate your any advice especially if you shoot film and print
digitally.
Jim
On Jan 13, 2020, at 9:56 AM, Iliah Borg <iliah.i.borg@xxxxxxxxx> wrote:
For Zones we use Y for base+fog or for the blank paper, not 100.
The reason for this is how Adams defined Zone X - it is not within the
dynamic range.
On Jan 13, 2020, at 9:42 AM, Brown, James William wrote:
Thank you all for your suggestions and solutions to getting a reflection
densitometer readings from a step wedge. From the last two days of research
and your helpful suggestions, I have figured this out.
I had stumbled on to a laborious process by saving the .sp file for each
reading, putting the data from the 10 readings into a txt file and
importing it into a spreadsheet. Then parse the row data into columns and
transpose the rows into columns.
The column data were copied and pasted into a spreadsheet downloaded from
http://www.brucelindbloom.com
That spreadsheet was used 10 times to get the visual density numbers.
Whew!
I knew there must be a better method and several of you (my educators)
provided the answer.
The Y value of XYZ can provide the reflection density result and is much,
much quicker to implement.
The formula I finally used in my spreadsheet was:
D= -LOG10(Y/100) where Y is the Y value of spotread’s XYZ.
I calculated the difference between Bruce Lindbloom’s visual density
derived from .sp files and the formula above. The average difference across
the 10 steps was .0001.
Thank you Graeme for planning to make this even easier with a -d feature
and thanks to all who work on Argyllcms. My 2004 Eye-One is no longer
obsolete.
I am beginning to have a modest understanding of the relationships in these
various measurements.
I look forward to learning more about other argyllcms programs.
Jim
--
Best regards,
Iliah Borg
LibRaw, LLC
www.libraw.org
www.rawdigger.com
www.fastrawviewer.com
