A
Tutorial on Using QuadTone RIP (PC version) to Create Digital Negatives
By Tim Gray
A few days after my tutorial
on platinum/palladium printing was published here on Luminous
Landscapes I received an email from
Ron Reeder (co-author of Digital Negatives: Using Photoshop
to Create Digital Negatives for Silver and Alternative Process Printing) expressing some concern
that I had characterized the use of Quadtone RIP (QTR) for printing digital
negatives as a “dead end”. He pointed me
to a recent update (May 2009) of his tutorial (version 3) on using QTR on a Mac
to create the negative. Here’s a link to where the QTR application and
user guides can be downloaded. My initial attempts at using QTR were based on a
previous version. Since I was already conceptually predisposed to the concept
of using a RIP instead of Photoshop curves I agreed to have another look based
on his updated content.
Before reporting the results I want to say
that being a PC user I found that combining the instructions for creating
digital negatives for a Mac and the QTR user guide for
the PC was not particularly intuitive. The
Mac method is quite different from the process for a PC since QTR for the PC
comes with a standalone printing application not available for the Mac. For
these reasons I’ve included a “short” tutorial on using the PC version of QTR
to create digital negatives – which should be applied in conjunction with the
most recent version of Ron’s tutorial.
________________________________________________________________
The
Results
In one word, excellent. In just a few days, with
only 8 iterations (one of which was a user error where I adjusted the
parameters in the wrong direction) I was able to produce a negative that was
noticeably superior to what I’d been generating with countless tweaks using a
combination of 2 Photoshop curves. The
timing was fortuitous as I was switching media from Pictorico to InkPress and
that required a major re-engineering of the profile. I do add one caveat: one of the purposes of
my original article was to highlight the pitfalls that a beginner might
experience – pitfalls that simply may not be apparent to a long term
practitioner and my initial experience with QTR in particular and digital
negatives in general was not atypical. I
suspect the ease with which I was able create high quality negatives over the
past couple of weeks using QTR is predicated at least to some extent on the time
I invested almost a year ago in attempting unsuccessfully to work through that
methodology. I hope this tutorial will
reduce at least some of the frustration that can occur when attempting to
master the process of creating a digital negative for platinum or palladium
printing.
Below (again suffering considerably from
translation to the web) are 2 samples of palladium prints. The first, on the left, is a scan of a ChartThrob
step wedge printed using Photoshop curves and the second is using QTR. Both have been converted to grayscale and
I’ve added a gradient to each step wedge since the wedge alone doesn’t tell the
whole story. In addition to being
significantly easier to derive, the QTR version has smoother tonality and a
more even gradation. The apparent graininess in the highlights is a
result of the Arches Platine paper texture.
Photoshop
curves QTR
You can stop here if you have only
a passing interest in the subject, but if you’re interested in actually making
a digital negative, and use an Epson printer (QTR only supports Epson, but
the same principles should apply to any RIP), I encourage you to press on!
________________________________________________________________
The
Process
QTR allows the user complete control of how
much ink is laid down for each of the available colours. This ability to closely manage ink density allows
you to establish the precise amount of ink needed to set the appropriate black
and white points without altering the native image in any way. QTR also has the capability of reading a
Photoshop .acv curve file to provide for any additional adjustments
required. This curve is created in Photoshop
only for convenience and is applied as part of the printing process from QTR with
no impact on the original file.
Here’s a screen grab of the QTR basic
print screen. This is pretty well self
explanatory, and I never encountered any difficulty in using it to print
traditional BW inkjets. Just mouse over
the Printer (top right) then select the Epson printer you’re using. The advanced adjustments aren’t used.
QTR print screen
On the off chance that you might be
using InkPress transparency film, the instructions that come with the media
indicate you should use 1440 dpi. I confirmed with them that the media handles
2880 without issue and I’ve encountered no problems.
I’ll also note that the auto sheet feed works fine for single sheets of
the film, eliminating the frustration of hand feeding.
The only real choice for this page, other
than which profile (ie: curve) to use, is which ink: photo or matt black. You can decide by calling up Calibration Mode
(Tools; Options; Calibration Mode). This
loads a color file with each row representing a specific ink. Print this image on your film (you have no
choice but to print as a positive) and make a pt/pd print. You can look at the K (black) and MK (matt
black) rows and select which one has more white (ie least transmission of UV
light) and choose that ink. For me, the
K ink was marginally more effective than MK.
________________________________________________________________
Editing
the QTR Profile
There are 2 ways to edit the profile: first,
using a text editor (Notepad seems to work best), or second, the QTR interface
under Tools; Curve Creation. When QTR is
installed, 2 directories are created under the QuadToneRIP directory: Profiles
and QuadTone. Profiles contains further
sub directories for each of the printer/ink combinations supported and each of
these sub-directories contains files with .QIDF extensions, one .QIDF file for
each paper (and neutral, cool, warm etc. characteristics). These .QIDF files are editable either as text
files in Notepad, or through the QTR interface. The second directory contains the same printer
structure and a .QUAD file that corresponds to each .QIDF file. The .QUAD files are not editable and these
are the ones actually used by the application to print.
If you edit the .QIDF file in QTR and save
it, there is no issue since the process of saving the file in QTR creates the
required .QUAD file. The trap is that if
you edit the .QDIF file in a text editor, after saving the changes (no spaces
in the name are allowed), you MUST go
back into QTR, under Curve Creation, select and open the file just edited and
then save it from QTR, otherwise the .QUAD file is never generated and that curve
profile won’t be on the Curve 1 drop down list from the Print screen.
When you want to print using the adjusted profile,
select that file from the drop down for Curve 1 in the Curve Setup section of
the print page. Curve 2 is not
used. (As an aside, for printing in BW,
a number of the curves provided with the basic install have no “neutral”
curves. Instead Curve 1 is loaded with
a warm curve and Curve 2 is loaded with a cool curve – or vice versa - and the
Curve Blending is set to 50/50 for the Highlights, Midtones and Shadows.)
Here’s a screen grab of the main screen of
the Curve Creation dialog in QTR showing the parameters I’m currently using
followed by the text file of the same profile printed from the .QIDF file. Since the terminology of the text files
doesn’t entirely map to the user interface, the numbers in red map the
variables in the Ink Setup page to the text printout.
Qtr curve creation
#Notes 1 June 21 2009, 20:56 25
18 32
#Notes 2 June 22 2009, 18:40 12
09 50
#Notes 3 June 22 2009, 19:43 25
15 20
#Notes 4 June 25 2009, 16:25 20
13 17
#Notes 5 June 26 2009, 16:30 25
10 12
#Notes 6 June 26 2009 18:22
30 10 12
#Notes 7 June 27 2009 08:29
30 15 12
#Notes 8 June 27 2009 09:25
30 12 12
PRINTER=Quad4000
CURVE_NAME=RR4000-Pd-test-8-1
GRAPH_CURVE=YES
N_OF_INKS=7
DEFAULT_INK_LIMIT=100 1
BOOST_K=30 2
LIMIT_K=12 4
LIMIT_C=12 4
LIMIT_M=12 4
LIMIT_Y=12 4
LIMIT_LC=12 6
LIMIT_LM=12 6
LIMIT_LK=12 6
N_OF_GRAY_PARTS=2
GRAY_INK_1=K
GRAY_VAL_1=100 3
GRAY_INK_2=LK
GRAY_VAL_2=24 7
GRAY_HIGHLIGHT=0
GRAY_SHADOW=0
GRAY_OVERLAP=
GRAY_GAMMA=1
GRAY_CURVE=C:\tim_qtr\qtr-8-1-grayscale.acv
N_OF_TONER_PARTS=0
TONER_HIGHLIGHT=0
TONER_SHADOW=0
TONER_GAMMA=
TONER_CURVE=
N_OF_TONER_2_PARTS=0
TONER_2_HIGHLIGHT=0
TONER_2_SHADOW=0
TONER_2_GAMMA=
TONER_2_CURVE=
N_OF_UNUSED=0
COPY_CURVE_C=K 5
COPY_CURVE_M=K 5
COPY_CURVE_Y=K 5
COPY_CURVE_LC=LK 5
COPY_CURVE_LM=LK 5
The above is for an Epson 4000 and
from Ron’s Articles site you can
download a sample for the newer printers with an additional Light Light Black Ink.
There are instructions in version 3 of the user guide on how to adjust
the profile for those printers. The
basic idea is to forget about using the LLB ink.
The Ink Setup page is really the only one
you need to tweak. For the remaining tabs, here are the default parameters:
Gray
Curve: Highlight = 0; Shadow = 0; Overlap = blank;
Gamma = 1. If you use a Photoshop .acv
curve the location goes in the Curve box.
(More on the curve later).
The Toner
Curve and Toner 2 Curve are both
Highlight = 0; Shadow = 0; Gamma = blank and no curve.
Linearization is blank
Notes are whatever notes you want to record. It’s useful to use this to record an ongoing
diary of your progress. You can see from
the .QIDF printout above that I’ve tracked each of the 8 iterations. After the date and time, the 3 numbers are
the Black Boost, Dark Ink Limit and Light Ink Limit respectively.
The easiest way to create a new curve is to
click on Tools from the Print application, select Curves Creation; File; Open
an existing curve, apply the changes then save it
under a new name (no blanks in the name).
After you’ve saved it, it’s interesting to look at the ink density
curves that QTR applies, by clicking on Show Curve available on any of the
Curve Creator screens.
Here’s a quick outline of what the
variables on the Curve Creator Ink Setup screen mean.
Default
Ink Limit: is set to 100 but is overridden by the
individual Limits set for each ink. The
Limit is the maximum amount of ink that will be laid down for any of the colors.
Black
Boost: sets an exponential boost to the K ink
limit.
Black
(K): set to Gray Ink, this is QTR’s default
curve for the black ink – the drop down lets you choose other curves,
but that isn’t necessary.
Density: always set to 100
Limit: set to what ever works – this limits the amount of the specific
ink laid down.
Cyan
(C) Copy Curve from K: takes the same curve as set
under the Black (K) variable. Similarly
the Density follows K and the Limit can be set independently.
Magenta
and Yellow have the same
explanation as does Cyan.
Light
Cyan (LC): copies the curve from LK (the QTR
default curve for LK) and the Limit is set to whatever works. Similarly for Light
Magenta.
Light
Black (LK): Density is the point at which K takes
over from LK and doesn’t need to be changed since I understand this to be a characteristic
of the ink set. In Ron’s tutorial he
notes that for Ultrachrome Inks the number is 24 and for K7 it’s 30. More technically, in this example 24 is the K
ink limit that corresponds to a 100 limit for LK.
While you can tweak each color’s Limit
independently, it’s easiest to treat each of C, M, Y, and K to the same limit
and LC, LM and LK to a separate limit. It’s purely coincidental that the limits
for the dark and light inks are the same in this profile. But the fact that all the dark inks are the
same and all the light inks are the same is intentional. It should go without saying that the printed
negative may have a color cast. This is
totally irrelevant since it’s only the UV transmission characteristics that matter.
The following is an illustration of the
Show Curve display for the above profile.
The vertical axis is the “ink limit” and the horizontal axis goes from
light to dark (as the ink is laid down on the negative) – ie: going from total
transmission of UV light on the left to total opacity on the right. The red numbers relate back to the screen
grab of the Ink Setup Dialog in QTR. If
you play with the variables and do a Show Curve for each
iteration, it’s easy to see what’s going on.
QTR Show Curve.
The red numbers map to the text output and Curve
Creation above.
On his articles page noted previously, Ron
has sample profiles for pd prints for the Epson 4000
and 3800. He cautions, and I reiterate,
that while these are reasonable starting points you really need to adjust these
based on your environment. For example,
my Epson 4000 profile is quite different:
I use a different concentration of Na2 contrast agent and a different
film media.
________________________________________________________________
The
Iterations:
So by now you’ve probably figured
out that the amount of dark ink laid down on the negative sets how the highlights
in the positive image come out and the light inks drive the shadows. The iteration process is relatively straight
forward. Start by adjusting the light
ink limits so that in the shadows you can just barely discern the difference
between the 2 darkest steps. If you’re
using ChartThrob, I don’t mean the difference between the 100th and
the 101st steps, but based on the left hand column or the small wedge
on the right hand side of the chart.
Similarly for the dark inks and the lightest of the steps. These 2 variables can be modified at the same
time. Once these Limits have been
optimized you can adjust the Black Boost variable to drive how fast you move
from paper white to the darker shades.
If you look at the .QIDF printout above and the notes of the progression
of my iterations you’ll see that I was unable to resist the temptation to
adjust all 3 variables at the same time.
By playing with the Show Curve display you can see where the effect of
changing the Black Boost will happen – 2 in the QTR Show Curve
illustration above.
Tweaking with a curve.
At this point in my own process I ended up
with a profile that was very good, without a supplemental adjustment curve
(what a pleasant surprise!), but I wanted to see what incremental improvement
could be made by tweaking the curve. I could
tell from the step wedge that the tonality was already very linear so I knew
that any curve adjustments would be minor.
As I mentioned in the main article one of
this difficulties I had with using the “scan and measure” technique of curve
generation was that the output of my scanner was off kilter. The scanner, an Epson V200 photo (cheap, I
know) is profiled with Mike Chaney’s profile
prism. His software includes an
assessment of the quality of the profile and mine was “poor”. Here’s the problem: the following is a scan
of a QTR inkjet print of the ChartThrob wedge file. The print is perfectly fine and should
generate basically no adjustment curve from ChartThrob. Instead, this is the curve that results:
Inkjet adjustment curve
In a perfect world this would be a straight line on
the diagonal, ie no variation.
Based on the assumption that the scanner’s
output, if not accurate, is at least consistent, I decided to use the above
curve as the reference against which to compare a QTR pd
print of the same file.
Here’s a rundown of the process. This may seem a bit complex
but basically all that’s happening is that a scan of a pt/pd print is
being compared to a scan of an inkjet print and the differences used to create
a normalized adjustment curve for the pt/pd. ChartThrob isn’t strictly
necessary for this process, any step wedge will serve. I use ChartThrob
because it applies a blur; average separately against each step of the wedge
and I find this works a bit better than applying a uniform Gaussian blur
to the entire image.
1. Run the ChartThrob script from Photoshop to create
a step wedge file.
2. ChartThrob’s file is 8 bit so convert to
16 bits.
3. Add a gradient section to the top as per the previous
illustrations. This has no impact on the actual process but the gradient
gives a more intuitive feel for the quality of the profile than simply looking
at the various steps.
4. Use Photoshop (or QTR) to make a normal inkjet
print of ChartThrob.
5. Scan and load the inkjet print back into Photoshop
but leave in RGB, ChartThrob insists on an RGB file so Grayscale won’t
work for this step. Set the appropriate black and white points – it’s
important to use the same method for setting the black and white points in
both the scan of the inkjet and the subsequent pd/pt positive.
6. Run the ChartThrob script to generate an .acv curve. The
curve that’s generated has no value (in my case – your mileage
may vary) but the script does a nice job of doing a “blur; average” separately
to each step of the wedge.
7. Invert the image – since you will be printing
negatives with QTR, the normalization must be done against a negative.
8. Measure and note the value of 16 steps including
0 and 255. You want more samples in the toe and shoulder of the curve than
the mid tones, which are normally relatively linear.
9. Write these numbers down on a piece of paper or
enter into a spreadsheet.
10. Print a negative on film of the ChartThrob wedge and gradient using
QTR. In the Curve Setup section of the main printing page select the
profile you created with the Curve Creation dialog.
11. Print out normally using pt/pd methodology and scan the resulting
positive.
12. Load the scan into Photoshop and convert to BW (RBG, convert to BW
set black and white points etc.) and run the ChartThrob script to create a
curve and blur each step. Invert this image to a negative.
13. Measure the same steps and record the values to the right of the
first column. These paired values are the output/input values to create a
curve.
14. Go back to Photoshop and open any image (you simply need a working
space to create the curve). This time make sure the image is converted
to grayscale.
15. Create a curves layer and go into the curves dialog and under Curves
Display Options make sure Light is selected. When manually tweaking the
curve subsequently you need to remember that you are adjusting the ink on the
negative so if you want lighter shadows you need more ink on the negative so
you must drop the curve in the highlights area of the curve to make the negative
shadows darker. (Note: I know this is confusing – while this example
is predicated on a Curves Display Option of “Light” developing
the curve using the “Ink” setting may help clarify the process.)
16. Drop a point anywhere on the curve and enter the Output/Input coordinates
for that first point. The first column (the results from the inkjet reference
print) is the Output and the second column (the results from the pt/pd print)
is the Input. Drop a second point on the curve and enter the coordinates
for the second measurement. Repeat for all the data points you measured.
17. Once the curve has been created, save someplace you can easily
browse to (again, no spaces in the name).
18. From the Gray Curve tab in the QTR Curve Creator browse to the .acv
curve and select. The following is why it’s important for the curve
to have been generated from a grayscale image: if it’s not grayscale,
you’ll get a cryptic error message when you go to save the QTR Curve
and the Curve Creation will fail.
Here are the data points I noted (including 255 and 0). The first column
is from the pd image and the second column is from the Inkjet reference.
PD |
Inkjet |
Output |
Input |
0 |
0 |
23 |
16 |
44 |
44 |
60 |
62 |
76 |
80 |
90 |
97 |
134 |
138 |
158 |
164 |
184 |
190 |
204 |
211 |
214 |
223 |
226 |
234 |
234 |
239 |
244 |
249 |
250 |
249 |
255 |
255 |
And this is how the above curve looks. In point of fact it seems that the variation
from a straight line is within the error of the scanning process because
applying this curve in QTR results, to my eye, in a print that is less
satisfactory than using no curve whatsoever.
This is probably more good luck than good execution. You should probably smooth out the curve and
it can be tweaked as desired in Photoshop.
Final curve sample.
I’d
be happy to hear any comments either through the Luminous Landscape discussion
forum, or email via my web site: www.timgrayphotography.com
January, 2010
________________________________________________________________
About Tim Gray
Tim was raised in Calgary Alberta but has called Toronto Ontario home for the
past 20+ years. He acquired his first digital camera in 1999, when 2 mpx
was considered “high resolution”. His immediate objective was
photographing the millennial fireworks from his condo window. That Nikon
Coolpix 950 camera, an Epson 1270 printer and the fireworks were enough to
trigger a passion for photography that grows every year. Preferring the simple
landscape, his photography has taken him from the cityscapes of downtown
Toronto to as far afield as Antarctica. Lacking experience in the analog
darkroom Tim felt a desire to connect with some of the deep historical roots
of photography and acquired a taste for the time honored technique of hand
printing with platinum and palladium. Tim’s work (but alas, not the
noble metal prints) can be viewed, and he can be reached via his website:
www.timgrayphotography.com.
