QTR,dMax and other stuff
2005-01-30 by Fred Drury
For openers, let me echo the observations of others and salute this group for its contributions to the art, and its focus on helping everyone on the list improve their results. It truly is a great forum and an incredible source of not only information but also inspiration. Thanks to all of you ... I find value every day's messages! In a recent message to the list Steve Kale described his technique for countering what he describes as flatness in QTR prints. In part he suggested: If you want to see on screen the effect this weak dMax and QTR's > linearization do the following. Open a Gray Gamma 2.2 step wedge. Add a > Curves Layer (Layer->New Adjustment Layer->Curves->Enter). Grab > the bottom > left anchor point and slide it up to (0,41) and grab the top right anchor > and pull it down to (255,243). Now look at how the input/outputs for the > points in the middle have changed eg 128. For the most part, the image is > lighter because the better part of the straight line has been shifted up > (128 has gone to 142). (Note that there is still nice visual separation > between the steps on the screen which is QTR's linearization goal.) When > people say an image is flat it is largely, I believe, because all the > mid-tones have been brightened. He also suggested a method for countering the 'flatness' problem: Add another curves layer. Lock (128,128). Grab (63,63) and pull it down a > little say to (63,43). Grab (192,192) and shift it up a little say to > (192,213). This is what is meant by an s-curve - it is shaped like an s. > You are adding a little punch to the highlights and darkening the > shadows a > little without shifting the mid. You can view the effect of the second > curve by itself by turning the visibility of the first off. The effect on > the image though will be the two curves combined. The selection of points > and how much to move them is really an artistic one but you have to judge > the two together which is why I said keep the first curve visible. Note > that the first curve (a representation or simulation of what the RIP is > doing) shifted the mid up point up and the second left it the same - ie > still up. So your mid grey will still be lighter than the original image > without the curves. You might choose to pull the mid darker in the second > curve to counteract the effect of the RIP. It's up to you. I have done some experimenting with this method and thought I would both share the results with the group and seek suggestions for further experimentation. I first printed the image using QTR on EEM along with a 21 step wedge file. I'm printing on a 1280, using the MIS UT2 CIS and Roy's 'neutral-2' profile, 1440 super, Better. Measuring the step wedge with my i1-Photo instrument gave the following results 'L' results: 100%(black) -17, 90%-26, 80%-35, 70%-42, 60%-51, 50%-57, 0% (paper)-97. I then used a applied an 'S' curve of the type Steve described, reprinted on the same sheet of EEM along with another 21 step wedge file. The contrast was clearly increased and the image had substantially increased 'punch'. Comparable results were: 100%(black) -17, 90%-22, 80%-28, 70%-36, 60%-47, 50%-57, 0% (paper)-97. The lowering of the 'L' values in the 60-90% range (and increased values in the 10-40% range) did produce a more attractive result. A couple of questions for the group: 1) The L=17 value corresponds to an RGB result of something like 46,46,46 ... ... is this the best (darkest) black I can expect to obtain using EEM? (Note: The 100%(black) result on Premium Luster (neutral-3 profile) was L=6) 2) What alternate papers could I choose that would improve my blacks?, and how much improvement should I expect? 3) Is there a way to convert my measurements to an equivalent dMax... alternatively, how can I measure dMax? 4) Would working in Roy's recently posted Lab grayscale workspace permit moves towards improvement? Some further questions for the group (I'm working with a PC system and so am anxiously awaiting the information on how those of us in PC land can go about making profiles): 1) Does anyone on the forum have any idea when this information is likely to be available? 2) I gather we PC'ers cannot currently do any soft proofing either? With many thanks to this forum for past and future assistance, Fred Drury Markland Imaging