Wednesday, April 11, 2012

Calibration Project Competed!

Again, the best source for the description and control of the process in my opinion is Ron Reeder, cited earlier.

The multi-ink curve which currently works for me sets a limit on the dark inks at 20 and the light inks at 24. This is up from the 14-18 at which I started. I found this through printing of various settings from 14-18 to 20-24 (otherwise known as trial and error). I started with a gamma setting of "1" rather than "0.7" which in preliminary trials did not work well for me. The setting of the correction curve in fact took care of the gamma and the crossover point. I found I was able to "tweak" the curve to adjust for slight anomalies of smoothness in the almost-right print ranges. But only very small changes can be implemented at this stage.

There are still some small deviations from the ideal step wedge in the lightest ranges of the positive print, but I find them tolerable, even preferable, on the test prints of actual subjects that I've run. I've tended to accept less-than-white-white on previous curves and enjoy the entire range from bright white to black black. In the future I may want to try to smooth out the range from 85-100 on the positive print. The blacks run to black a little too quickly from 88-96 for example, so I might lose some details in the deep shadows of the positive print. But overall, I'm quite satisfied with the tonal range -- and with the palladium printing technique.

The Curves for the Corrected Print

The curve at the bottom is a correction curve made in Photoshop. It compensates for the deviations from the "K" or blackness on the palladium print as compared to ideal stepwedge values.

Then next curve up shows the ink distributions in the printer program QTR after the correction. In fact, 8 inks are used, but most copy other curves. This is quite smooth and produces enough ink to provide a real spectrum of linearized tones via the ultra-violet exposure.

The corrections are made by using a scanner as a densinometer to determine the actual "K" readings in the palladium print.

These instructions are fed to the QTR program via a *.qdif file which is an ASCII file. This is the file which produced the corrected curve:


Tuesday, April 10, 2012

The Corrected Image

This is the corrected print. It is no longer "muddy". The whites are much whiter and the blacks now stand out.

The digital negative is darker than one would expect. What counts is how much UV lights gets through. The standard for a silver gelatin negative is whether you can just read a newspaper through it. That is not true here, though you can read some typescript in the lightest areas.

Correcting Tones in Palladium Printing

This "muddy" print needs to be corrected. The whites need to be whiter and the blacks, blacker. This can be accomplished by linearizing the tones, especially the mid-tones, of this print.

This can be accomplished by calibrating tones accurately to a gray step wedge. This can be done with standard step wedges and a process described by Ron Reeder and others.

Once applied, the results are dramatic, as can be seen in the subsequent posting.

Friday, April 6, 2012

Sense of the Distant Past for the iPad

I've been intrigued with Blurb's forward thinking on publishing both hard copy and eBooks. It's quite simple to convert the *.pdf associated with a book published by Blurb to an *.epub format which can be read on the iPad. Blurb makes it possible to buy an iPad version of an existing book for $1.99. I find the quality remarkable, better than using Blurb's Viewer to preview the book. One can flip pages or zoom in. The print-quality DPI comes in handy here. Once downloaded, the eBook will appear in the iBooks library.

Once set up, anyone with an iPad/iPhone viewing the "Sell" page for a Blurb book will have the option to purchase the iPad/iPhone version in addition to the hard copy options. Click here to go to the "Sell" page. In you are simply interested in the technology, I think you'll find it's worth $1.99. If you are interested in palladium prints, well, that will make it a real value!

Blurb also makes it possible to set up a way to sell the same book through Apple. In this case, you need an ISBN number and a pricing understanding. Typically, a book is priced about $9.99, where the author receives about half. This, however, is only available some Blurb Beta users.

Interestingly, if you sell through Blurb, it doesn't appear that you can set a profit margin and the whole $1.99 goes to Blurb. If you sell through Apple, you cannot continue to sell through Blurb, but of course you can set your price. [NOTE: April 10. You can set the profit margin for Blurb-published eBooks, once you have bought a single copy. I'll update to $9.99 May 1st.]

I'm planning to sell botth the Sense of the Distant Past and Xinjiang: From the Karakorams to Hemu on Apple for $9.99 beginning in May. But whether sold from Blurb or Apple, the eBook is the same and ends up in your iBooks library. So you can save $8 until I shift over to Apple. :) [NOTE: April 10. I did update the price of the former book to $9.99 as of today.]

Monday, April 2, 2012

Calibration Sources

There are are several sources which are helpful in creating curves. I'm partial to Ron Reeder's book on digital negatives from Ron offers the clearest and most reliable account of making adjustment curves and a most interesting website.

Tim Gray had two excellent articles in the Luminous Landscape, the second confirming Ron's curve-writing for the QTR program for the Epson. In it he described a program called Chartthrob which runs as a script in Photoshop.

I've since tried quite clever program which enables you 1) to generate a grayscale step tablet of which you make a palladium print and then 2) to "analyze" the result. This feature actually generates a compensatory curve which appears as a layer mask adjustment. Like the author, Tim Gray, however, I was unable to come up with consistent results.

I have since worked along the lines that Ron laid out. Not all of the curve creation features are active in QTR for the 4900, but Roy Harrington, the author of QTR, pointed out in his release notes that it is possible to manually create a curve in a textfile, something I was able to do utilizing one of the "new" colors (orange) of the 4900. I still need to tweak that one a bit.

The curve creation tool in QTR works fine if you don't use the "new" colors orange or green. I have two curves that are almost there. I've learned to "tweak" the Photoshop-produced *.acv file that you include as the gray curve in QTR.

I've gotten one QTR curve and embedded gray curve that is spot on until you get to the 80% patch of a positive palladium print of Ron's stepwedge. From 80-100% the actual positive print is a little lighter than it should be. For example, the patch that should be 85% is only 79% in terms of "K" (or darkness) units. 90% is only 81%, etc. I think I have corrected this at just this end of the spectrum. The challenge is to correct these values while not "uncorrecting" everything else. Will keep you posted.