Methods for Creating a Mask for a DUP/DLP 3D Printer (running NanoDLP)

As evidenced by recent posts on this blog I have been busy creating masks for my Wanhao D7 printers.  I actually have masks that work but what I don't have is an easy process that can be done by anyone without a lot of extra hardware or specific knowledge.

Some of the techniques that can be used to create a mask are as follows:

Mask Creation Wizard of NanoDLP	Tools needed:  Light meter
Process: Project a grid of cells for measurement and adjustment.  Find the lowest light intensity cell using the light meter.  It will be one of the corners.  Note the light meter reading.  Adjust the grey value in all the other cells to match that of the lowest cell just noted.  Press the button to generate a new mask image.
Advantages:  Minimal investment in tools and/or technology (can even use a multimeter connected to a battery and voltage divider photo resistor as discussed here).	Disadvantage: Cumbersome and extremely tedious process.
Comments: Remember that the default screen orientation in NanoDLP is not the orientation of the Wanhao D7!

Measure, Calculate, Generate Mask	Tools needed:  Light meter and software to generate a mask. Note that I have developed two light meters that I need to release to the public domain. Both based on Arduino Nano's.
Process: Measure the light intensity using either a physical grid or the grid of cells projected by NanoDLP.  Use that set of measurements to model the mask with output being either an actual image file or the inputs needed by the NanoDLP Mask Generation Wizard.
Advantages:     Moderate need for additional tools and/or technology.  Relatively easy process.  Flexibility to use the data to generate masks for different uses of the build plate.	Disadvantage: Thus far there has been limited success in creating a really good mask using this technique.
Comments: Garage Science has a piece of software that does build a mask but it does not seem to work for the D7 resolution.  When I fed it data from a D7, but using a lower resolution in the same aspect ratio, the mask was no more effective than the Excel model that I have developed.  A number of people on the Wanhao D7 FB Group has said that a model will not work but I do not understand why.  I am assuming it is just a matter of my not having the right maths skills!

Measure, Automatically Adjust, Generate Mask	Tools needed:  Light meter integrated with  software running on the printer attached Raspberry Pi..
Process: Measure the light intensity using either a physical grid or the grid of cells projected by NanoDLP.  First find the dimmest corner.  Then project a grid of cells, one at a time, so the meter can be placed on each cell.  With the meter measuring the cell adjust its intensity using a mask value until it is equal to that of the lowest cell.  Output the matrix of mask values for input to NanoDLP (or generate a mask).
Advantages:  Should generate an excellent mask (though I have not had time to do so yet). Easy to run once set up.	Disadvantage: Fairly complex requirement for integrating a meter and software solution.

Photo Interpretation	Tools needed:  Camera (e.g Smartphone) and Image Processing Software (e.g. Gimp, Photoshop, etc)
Process: Take a photo of the light pattern projected by the UV LEDs.  Manipulate it into a mask using something like Gimp or Photoshop.
Advantages:  Can be done without any addition of hardware or software on the printer	Disadvantage: Requires a very fiddly setup for the camera to be positioned above the build plate precisely.  Fairly complex process of translating the image to a mask.
Comments: I think this approach is the most promising to meet my requirement of something that most people could do.