Curve Merging or Averaging

[mkochsch]

What's the easiest way to add two ACV files, or curve files, together? What I'm currently doing is making a second curve to "fine tune" the first curve and then reapplying the second curve after I've applied the first curve. What I would like to do is merge the two curves together as a new curve file.
~m

[Joe Lipka]

I believe that you could just apply the curves to succeeding layers and that would accomplish your goal.

But then again, it would require experimentation to be sure...

[jd callow]

I think Joe is correct. You could also try to add/subtract the differrences of your inputs and outputs manualy. I suspect that you are looking for an automated method that will merge the curves and I don't know of one.

[amphoto]

Alternatively, what you can do is apply each curve in succession to a standard greyscale step tablet (in photoshop), and then measure the altered values of the step tablet after both these curves have been applied. You can thus build a composite adjustment curve in much the same way that you build a standard adjustment curve.

[mkochsch]

I believe that you could just apply the curves to succeeding layers and that would accomplish your goal.

But then again, it would require experimentation to be sure...

I'm already doing that. I think were I'm wanting to go is a way of visually comparing curves. Ideally, if I could open two or more curves in a program window and compare how changing certain darkroom variables is affect the slope of the curve, the toe, the shoulder, the density. A tweaker utility.

[Joe Lipka]

You just solved your problem. Copy your photo so you have two versions, one with each curve. Open both at one time and experiment with the curves as you like.

That's one approach.

[mkochsch]

You just solved your problem. Copy your photo so you have two versions, one with each curve. Open both at one time and experiment with the curves as you like.

That's one approach.

Let me clarify....After running a curve calibration, if one applies the resulting curve to another calibration target further adjustments and improvements to the original curve can be made. It's possible even a third iteration would yield an even better curve. Liam Lawless proposed such a method in Post Factory #9 ["Tweaking the Digital Negative", p.36]. The problem is doing this by hand is painfully slow.
Changes in humidity, coating method, temperature, time etc. all may affect the emulsion on the calibration targets when printed. One person I know will actually print out a half dozen or more and averages the results. If I could take the six curves from that person's calibration images and average them into one curve it would simplify things. No dealing with multiple layers of curves, having to remember to turn on or off certain layers. Produce just one really good curve.
A system like this would also have the advantage of letting us compare how curves are changing over time -- easily. Kind of like running the calibration on your monitor every two or three weeks. Also, one could compare curves from different coloured emulsions in the same family or different families altogether.

I've taken the first step toward writing a program to do this. I'm not a programmer by trade so it might a little time.
Guillermo Luijk the author of Tone Hacker (if you haven't checked it out yet http://perso.wanadoo.es/j.luijk) has already given me some help and tips on reading the binary acv file. I now know how it is formatted and can read it. So now it's time to lock myself in woodshed and see where it leads me...a pui tarde.
~m

[Colin Graham]

Probably I'm looking for something completely different, but I've been playing with multiple curves a little today and the only luck I've has so far is applying the secondary curve first, before all the drama of the main curve is added, otherwise the tones I want to tweak are impossible to locate. But next I'm going to try applying each curve on a seperate layer and merging before inverting and filling, seems like this may be the most neutral and 'WYSIWYG' route. It would be very nice to be able to overlay 2 or more curves, to be able to compare them visually.

edit- Just tried the 2 seperate curve layers and it added a surprising amount of density compared to the sequential curves on the background layer...So I probably need to experiment with the blend options.

[mkochsch]

Pierre-Oliver is working on an idea like that here:
http://www.pierreoliviertavernier.com/Joomla
The software is still in it's infancy but it's coming along. Works using Paint Shop Pro (free to 30 day demo) and not PhotoShop however.
~m

[sanking]

The problem is doing this by hand is painfully slow.
Changes in humidity, coating method, temperature, time etc. all may affect the emulsion on the calibration targets when printed. One person I know will actually print out a half dozen or more and averages the results. If I could take the six curves from that person's calibration images and average them into one curve it would simplify things. No dealing with multiple layers of curves, having to remember to turn on or off certain layers. Produce just one really good curve.
\

If the objective is to combine several curves to produce a curve that compensates for the inconsistencies of process it would seem to me that the average curve is destined to produce less than ideal results most of the time.

The best practice IMO is to learn what is necessary so that you can always get repeatable results with the process, then you would have only one curve that is pretty much perfect. This means temperature and humidity control in the workroom, and consistent procedures of coating and drying.

Sandy