Re: Sources for stochastic screens
Hi Jon, and thanks for the words of enlightenment and encouragement... I do understand more now that you explained a little of what must be basic stuff to you, but was Greek to me. I do have Dan's book, and will go back to that and do some studying... two steps forward, one step back :o) Susan gravure blog at www.susanvossgravures.blogspot.com website www.dalyvoss.com On 2/25/07, Jon Lybrook <jon@terabear.com> wrote: Hi Susan, I know what you mean. We all just want it to work, unless you've got exactly the same hardware as I do and are creating and processing plates in exactly the same manner, using my curve without any adjusting of your own will almost certainly not be as good. Consider any curve supplied to you from someone else a starting point - you'll need to learn to tweak it to get the results you want, I'm afraid. I think I mentioned before, I wouldn't use the curve posted on my website when using a coarser scree or plates other than the KM73. This is because the curve was designed specifically with a KM73 plate and finer stochastic screen in mind. There are other variables that require you to tweak the curve: Your inkjet printer may output transparencies with more or less density than mine as well -- you'll want to adjust your curve or exposure times as a result of your testing. A curve compensates for the fact that we're transferring an image from one medium to another. Images generally gain contrast, as they "lose data" -- Much like when you copy 3rd and 4th generations of audio tapes ... the fidelity of copies of copies start to become less defined. Compensation curves adjust for a known and expected loss in certain areas of density. When I said 100% maps to 82%, I mean the 100% blacks are adjusted to actually be 82% when output on the inkjet printer. That's what Chris meant by Input 100/Output 80 as well. We do this because if we didn't, all the shadows from 100-82% black would all look the same -- we wouldn't have as much shadow detail. How do we know? Because we've done tests and tweaked our process, exposure times, and curve with each successive test (though usually one thing at a time is best of course :-)). Curves are one of the best control tools we've got to make images look like we think they should when using digital images for alt processes. Dan Burkholder has an excellent "Tiny Tutorial" on creating curves, why and how to do it here: http://www.danburkholder.com/Pages/right_frame_pages/turtorial-right-frame.html# Click on Adjusting Digital Negative Curves. Dan makes it more fun than it would be otherwise. His book is also a great resource if you don't already have it. If you don't, buy it and if you do, read it! :-) Cheers, Jon SusanV wrote: Jon and Chris.. Great work on all this screen information. Another reason this list and the people on it are such treasures! As for the curves discussions, I must admit that when I start reading about those things, my hair hurts. I'm just not up to speed when it comes to curves (as relating to digital positive/negatives for alt process output). I don't even understand a lot of the terms you all use ( "100% mapped to about 82%", "moving the point top right down to Input 100/Output80" ....SAY WHAT????? ). I'm just late to this digital neg/pos party you've all been doing for a while now. I'm not at all a technophobe... but in this particular instance, I just want a simple solution to get me making my images. I'm using Jon's curves at this point, but I do wish I understood how to tweak them to get the best result for my own workflow with the 1280 printer and Nuarc and km73 plates, etc... ok, i'll stop whining, haha... it's just been a killer week here and I'm wiped out. I'll go take a nap and come back later :o) susan www.susanvossgravures.blogspot.com www.dalyvoss.com
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