[Alt-photo] suggestions about cyanotype curve

Niranjan Patel nirpat89 at yahoo.com
Tue May 23 21:34:41 UTC 2017

Apologize for that goofy formatting....don't know what happened.  Another try:


Hi, Bob:

Not being able to see your attachments, but my experience of using the ChartThrob which I am assuming is somewhat similar to Peter Mhrar's technique you are using (of which I am unfamiliar) might be of value here. I encountered exact same problem as you on my first curve for Centennial POP after optimizing for Dmax with colorized negative. I think these auto-curve programs are less capable to give the “correct” correction curve in the areas of extreme variations, exacerbated greatly because of Photoshop's inability to have points that are close together. There are I am sure a number of ways to circumvent this problem. They all probably do the same thing, i.e. reduce the maximum density at the 100% (0% for the negative) step. The ink reduction is a logical step as suggested by others here. Here are a couple more:

1. Downgrade your “optimum” color for maximum opacity. The way I did was measure the RGB values on the colorized negative in Photoshop of the first or the lowest step that is all clear. Use those values as the color for the “color fill”layer. Now re-do the cyanotype and the curve generation.

 2. Use a simple post-inversion straight curve applied to your negative image below the color fill layer: Point 1 = (0,x) where x corresponds to that same lowest all clear step (inverted). For example for the 10th step at B= 10% it would be (255-230) = 25. And Point 2 = (255, 255). Redo the curve generation.   

 For my digi negs, I ended up using a combination of both of these in the end. Also I started doing the curves manually, the old fashioned way. 

Don't know if this makes sense or will help your particular case. As Keith S. says, it is easier to show than say. 



More information about the Alt-photo-process-list mailing list