Need Precision Curves Adjustment

[martinch]

Here's another thing that's keeping me stuck using PS for the near future, as I haven't found a suitable replacement in another application...

I require precise adjustments of curves for when I create calibrated contrast correction for alt process photo printing. I regularly print using gum pigment (aka, gum bichromate), kallitype, gumoil and cyanotype techniques. The overwhelming majority of my fine art prints are done this way. To get the best results, it is necessary create compensation curves to correct for the deficiencies of the print process. They are all different, and ideally one would create individual curves for each kind of paper used, as well as for the different processes. I feel confident saying this is the common practice amongst alt process photo printers these days, so I'm certainly not the only one who would benefit.

A full description of the process I use can be found here: https://www.freestylephoto.biz/alternative-process/making-digital-negatives Please take special note of Figures H and I in the article because these illustrate exactly what I'm needing to do with curves.

What I need is the ability to precisely input the required I/O numbers into the curves dialog. Not only do I not see any way to do this in AP's curves, I don't even see any sort of scale that would clue me in to where I am on the curve. I am able to read gray values the way I need with the eyedropper, but without being able accurately translate those numbers to a curve, I'm stuck with only half the tools I need to do this.

[martinch]

Also, lack of Gray Gamma 2.2 is annoying. I know that your Gray D50 claims to have a gamma of 2.2, but this still doesn't tell me whether it translates exactly to the same result as using Gray Gamma 2.2 profile.

[Old Bruce]

15 minutes ago, martinch said:

What I need is the ability to precisely input the required I/O numbers into the curves dialog.

I don't currently need this but I would really like to have it.

[jalamb]

I also want precision curve writing as I do corrections in LAB to take specific point (highlights, shadow, etc.) to specific values for certain papers. Using the picker doesn’t seem to work for the second point on the curve, but numeric input would be much easier even if the picker did work.

[Subclavius]

Hello martinch and Old Bruce,

If it's of interest, I posted this method in the tutorials section of the forum:

It was tested on a 1.7.0 beta but it appears to work in current production 1.7.2.  Any comments would be appreciated.

Nigel

[AlanG 2112]

Can I please add my voice to the request for the ability to create curves using the Input/output values as with Photoshop and for a Gamma Adjustment too. As others have posted, I do alt process photography Gum Prints and Cyanotypes and need these curves to be accurate to the ones calibrated by me for Photoshop. Not having these is pretty much the only thing stopping me from cancelling my Photoshop Subscription right now. Thank you. 

[Andy Somerfield]

Hi,

I'm pleased to say that we have implemented precise adjustment of curves using input / output values and it will become available in Photo 1.9 (which will go into beta in a few weeks).

Thanks,

Andy.

[Vasto7]

Currently there seems to be a way to precisely place a note on the curve.  If you add a node, you can move it to a known location such as x =0, y = 0.  Pressing the right arrow key twice will move the node to x = 1, y = 0.  Pressing the up arrow once will then move the node to x = 1, y = 1.  The vertical grid lines are at x = 64, 128, 192, 255.  The horizontal grid lines are at y = 64, 128, 192, 255.  With this information you can put a node at any coordinate, although it is obviously tedious to count the key strokes.  Nice that they are implementing a more direct method.

Regards.