kmcnally

I have read of people using both pigment and dye based inks with equally good results - but most seem to favour dye based inks. Not sure if someone has an opinion on this - I am open to any ideas on this process. Virtually every article I can find on this "method" go about linearising the curve in the same manner - a scanner - and seem to get good results. It just seems going forward on this idea that a scanner really is not the best tool for the job. If I scan a stouffer step wedge (with no colour correction) and use the levels tool to set the black & white points to values taken from a spectrophotometer (0% and 100%) - you would think that the LAB values between 0% and 100% might resemble something close to their actually LAB values read with a spectrophotometer - but they don't - they are always out - and I have tried five different scanners. The scanner(s) response does not seem to be linear. With this said, I cannot understand why we would then go about basing a correction curve on readings which in no way relate back to the contact printed step wedge that was scanned. Am I overthinking this?

From what I understand, pt/pd and some other alternative processes require high contrast/density negatives. This can pose a challenge to inkjet printers but I believe it can be accomplished using colours other than black alone which are more effective at blocking UV. The method above (http://glsmyth.com/articles/creating-the-digital-negative.pdf) describes printing a colour chart to transparency and checking which colour blocks UV most effectively for your given process (Part 3 in the PDF). The negatives are then colorised in photoshop using the determined colour value. This seems like a good way to do it - as if black ink alone were to be used, I "suspect" that the density's required would cause problems in itself (this is based from reading alone). I have seen some great pt/pd prints online which have been derived from digital negatives so I have a lot of hope for this hybrid process. For my purpose, I plan to use VC/MG paper - so will steer clear of colorised negatives due to the effect they may produce with contrast on these papers. If I later go with graded papers (providing there is any left by that time....) I may well colorise my negatives. For silver prints I understand the contrast and density requirements are nothing like those required for pt/pd etc...

http://glsmyth.com/articles/creating-the-digital-negative.pdf

Hi Bill, The plan is to print the 21 tone step wedge onto transparency which goes from 0% to 100% black in 5% increments and establish my baseline exposure which would make 100% as black as the paper allows with the least exposure possible. From there I would like to begin taking readings and plotting a curve to correct the non-linear way in which this will inevitably print (perhaps silver paper is more linear the pt/pd, salt etc...?). From readings, 50% gray on the step wedge will not print as 50% on the contact sheet - so the curve comes into play here to remap these tones according (say my contact she read 50% gray as 66% - my curve point would have an input=66 and output=50 to correct this). Unfortunately my spectrophotometer only produces reading in LAB and density - so in photoshop I plan to convert to the LAB color space and use L* reading instead of grayscale percentages. The article below explains the process I am going to go through here - it's just the scanner part of this I would like to try and rehash. Using a scanner to perform these sorts of measurements seems fraught with potential issues (especially since a calibrated scanner does not appear to be required in the first place).

Hi Bill, Thanks very much for the response. Sorry if I am coming across a tad vague - this is a new area to me and I still have much to learn here. :) That is something of an understatement... I suppose I am trying to characterise the whole process - paper, negative and ink via the linearisation of the curve. All the processes I have read about talk about printing a step wedge to the transparency film, establishing the baseline exposure to produce dMax on a given paper and then printing/developing the step wedge onto the chose paper (silver, pt/pd etc..). They all then explain how to scan this developed step wedge and before taking any measurements defining the white point as wedge step 1 and black point as wedge step 21 (in order to effectively measure the differences between analogue vs digital wedges this step seems absolutely vital). It is this scanning part that I would like to try and figure out an alternative. I would like to be able to read the values of the each step as L* (via the lab colour space) and utilise these readings to plot the correction/linearisation curve for the given paper, ink, transparency combination. What I keep getting confused about is how do I handle the black & white points. If I read the wedge black point with a spectrophotometer I will probably get a reading of say L*=5 and a white point of L*=96 (for example). In the digital domain, the first step would be to fine these values as L*=0 and L*=100 respectively. The question hinges on how do I go about normalising the curve with this taken into account? One thing I have thought "may" work would be to plot the curve using the L* reading taken with the spectrophotometer (0%, 5%, 10%, 20%, 30% - 95%, 100% etc...) including the black & white points of L*=5 and L*=96 (respectively). This would produce a low contrast curve with no dMax or dMin being achieved. Once this is done using the levels tool I could then define the black and white points as L*=0 and L*=100...? Would this work in anyones opinion? The problem here is every print will require the low contrast curve to be applied, then corrected with the levels tool for dMax and dMin to be achieved. I hope this makes sense... :) My head hurts, the more I read on this the more confused I seem to become. I hope I have explained better and that it does not come across like the ramblings of lunatic :) Much appreciated, Karl

Hi Photo.NET Members, I wonder if anyone here could help me out here to devise a method of linearising digital negative curves without the use of a scanner? I plan to use this to produce silver gelatine prints and who knows - maybe carbon/platinum prints later on. I feel that the use of a scanner to assist in curve creation inserts a number of variables which may lead to problems further down the road - and I also don't have a decent scanner with the dynamic range to even produce a 21 step wedge which I could use.... What I do have is a SpydePrint spectrophotometer which allows me to read the values of the printed step wedge providing both L*A*B and density values. What I cannot work out is how I go about plotting this information against the curve. My concern here is that the maximum black/white point readings from the contact printed step wedge will not be 100% black not 0% white - thus throwing off all the other values in the process. All the documents I have been able to find discuss using the levels tool to set the black & white points before and readings take place - so that the scanned (analogue) step wedge dMax/dMin values correctly match that of the original (digital) step wedge. This makes good sense in my mind as the dMax/DMin of the actual contact printed step wedge will likely never be 100% black or 0% white. I am completely new to this digital negative concept and have yet to print anything (my darkroom is still be put together). In the meantime I am trying to prepare and standardise my workflow. Reading the contact printed step wedge using the SpyderPrint seems like a far more accurate way of doing this instead of using a scanner. What do other people think? Ideally I would like to be able to read the values straight off the contact printed step wedge with the SpyderPrint and proceed with the curve creation without having to scan this. Also, I cannot use any RIP based software as I plan to use a canon for this process. Please could someone help a man out here? I think it would be great if this could be figured out and documented so others could benefit from a system which negates the need for a scanner and the variables that it may introduce. Thanks very much to everyone in advance. Karl