New darkroom calibration software.

[Pere Casals]

I'd request opinions and suggestions for a new software I'm developing (to be relesed as open source/freeware), intended to speed up darkroom technical procedures.

Motivation: a) To plot curves is boring, for DIY emulsion, BW slide reversal calibration, carbon calibration, paper calibration, paper contrast calibration for a RGB LED illumination of the enlarger, SCIM/CRM and calibrations for contrast color mask with Alan Ross method. b) Practicing a bit GDI+ I'll have to use, this was also a motivation.

Features:

1) Densitometer:

A pictorial Negative is scanned alongside the stouffer wedge, the red cells are dragged (mouse) on the stouffer, densities of the steps are in a configuration so the software can compare what gray levels are what densities, by moving the mouse to any spot on the negative we see what density is.

2) Curve families for Film calibration:

We place (wyswyg) the green cells on the contact copies osf the stouffer, we enter the exposure in LUX.S, then from densities in the stouffer we know exposure in each green cell, so the software knows the exposure in Lux·S and density for each step of each curve, a text file is generated with a data column for each wedge (All have same exoisure but each has a different development, see BTZS)

This file is imported in Exel so we can plot all curves instantly. So a film calibration requires scanning the contact copies of the stouffer alongside the stouffer itself, adjusting position of the step areas by dragging with mouse, and a click in the calibration button, and then data rows are in Excel, no densitometer, no manual data handling to make a calibration, just making an scan.

Until here it works nice yet, next is planned:

3) Paper calibrations.

4) Proofing silver gelatin paper result by selecting a paper calibration, a negative scanned alognside with a stouffer, and LUX.s exposure reading with lux meter on the easel without the negative. We can determine aproximate paper grade and exposure, this development step is necessari to to to the 5).

5) Generating a 3D LUT to be used in Ps, that will allow proofing the printing of a negative sandwiched with contrast color mask. In one Ps layer we have the image, with calibrated densities thanks to the stouffer that has been scanned with the negative. In the next layer we have the color mask for VC papers that we draw on the BW image. Nex is a applied the calibrated 3D LUT generated by this software that is to make the proofing, so wswyg the effect of the contrast mask.

The target is to make easy crafting a good contrast mask, sure some adjustments would be required in the darkroom when we see the real result on paper, but 90% of the work would be made without wasting paper.


Welcomed:

Any kind of critique, constructive or destructive. Ideas. Opinions about what components would be useful, possible additions. Volunteers to test the software while is developed to see how the thing goes.

I don't ask help for coding the software but that it would also be welcomed, PM for that.

IMHO a tool that boosts control in the darkroom would make optical printing more competitive, being easier to obtain sound results that now are only possible with hybrid system.

Well, perhaps this is also kind of hybrid process, because be make the contrast mask from digital, but at least we have an authentic optic projection crafting the image, helping with complex prints, but at same time allowing for adding any ammount of manual crafting, burning/dodging and the like.

[Larry Gebhardt]

Sounds interesting. A few suggestions:

- make work on mac, linux and windows
- put the code on github to enable collaboration
- support multiple step wedges
- support multiple step wedge layouts and density ranges

[Pere Casals]

- support multiple step wedges
- support multiple step wedge layouts and density ranges

It suports any wedge, you load a text configuration file of any wedge, just two rows, step number and calibrated density. When loading a Wedge the step count is updated, but it can we modified if we want:



It also supports any pattern, with mouse we place the first and last position, and we can also change the rectangle XY area size where we average the reading:

make work on mac, linux and windows
- put the code on github to enable collaboration

I'm a native windows programmer, perhaps in on github someone may help porting to mac/linux or making a cross platform app, I'm encapsulating in classes so it would be easier, perhaps dependence to gdi+ should be removed.

[Tin Can]

I would need a youtube tutorial.

Thanks!

[neil poulsen]

This is really interesting. Here are some of the calibrations in which I'd be interested. (Plus, recommended methodology to execute the calibration.)

A proper way for testing to use aperture adjustments to compensate for black and white film reciprocity failure, so that one need not rely on mfg graphs. (These are often not very complete.)

Testing for contrast grades on paper using a reflection densitometer.

If it helps, I use a particular routine in SYSTAT statistical software to plot my film curves; it works perfectly and doesn't assume any particular model. It's called "double-weighted least squares" analysis. All one needs to do to use it is enter two columns of numbers (zone number as the horizontal axis and densities measured using a transmission densitometer on the vertical axis) and say go. It does the rest. I've not taken the time to determine how this method relates to regular least squares analysis, but as I indicated, it works really well for these and many other types of curves.

[Jac@stafford.net]

This is really interesting. Here are some of the calibrations in which I'd be interested. (Plus, recommended methodology to execute the calibration.)

A proper way for testing to use aperture adjustments to compensate for black and white film reciprocity failure, so that one need not rely on mfg graphs. (These are often not very complete.)

Testing for contrast grades on paper using a reflection densitometer.

What ever happened to test strips or personal experience?

While not perfect what about Ilford's variable contrast heads and controllers for the dimwits?

[Pere Casals]

A proper way for testing to use aperture adjustments to compensate for black and white film reciprocity failure

This is supported yet, you know, this is a regular film calibration but we use long exposures with lower LUX for the contact copy. A way would be (with same development) exposing several contact strips with different intensity but with the proper shorter or longer time to have the same lux seconds, in the family of curves each would show what happens with different exposure time. We would have a graphs for each development showing different LIRF.

Another approach would be making graphs with a single exposure time in the graph but with each curve in the graph having a different development.

Testing for contrast grades on paper using a reflection densitometer.

This is the next that it will be added, there will be two wedges, the transmission one tells (from Lux.Second reaching the wedge) what exposure received each step in the paper. A second reflective wedge that would be scanned with the contact copied paper strips would be the reference to calculate the densities in the paper strips. Not much work from present development status.

routine in SYSTAT statistical software to plot my film curves;

Calibration output is a text file, (also for the moment there is a basic curve display working yet).



So you can import in Excel, in SYSTAT or many other. In this way one can plot and print curves with scales, colors etc in the way he likes, decimal separators can also be comma or colon.

Coulmns are Step ID, exposure in Lux·Second, H (Log exposure) and then there is a column for each strip densities. I should add a user custom label for each column for easy identification.

I would need a youtube tutorial.

Randy, beyond that, don't worry, if necessary we can use Teamviewer or Anydesk to solve it.

[Bill Burk]

I’d like to be able to read on my densitometer and enter values for each reading. (Support a ‘debugging’ mode if you would like to call it that).

In some cases users don’t know their Lux seconds. So it would be nice if you work backwards to it. The way I work backwards is to find the curve that met ISO/ASA and from the 0.1 speed point of that curve (and the box speed) deduce the Lux seconds. Also assume users will be a little inconsistent, don’t allow curves to cross but instead slide the exposure axis of misfits and report the exposure deviation.

Encourage users to spend the extra money on T2115C calibrated scales.

[Bill Burk]

Draw the ASA triangle. Show the selected points for contrast measures and support Kodak Contrast Index as well as other gamma, average gradient measures. Show a Time/CI curve.

[Bill Burk]

As well as support the Zone System N’s