The Road Ahead
I don’t plan to bombard you with regular posts, so there might be periods of intense boredom here. But given that they aren’t going to be coming regularly, subscribing to know when they do post is a good idea. It’s free to do (at some point I foresee a paid tier, but general dev updates will always be free).
That being said, I think it would be a good idea to go over what is working and the current roadmap to release is.
What is Done
Color models are moderately mature and give good results given quality inputs. They are still likely to be tweaked given input and to support more options, but they give great results now.
Traditional Backlit AND Front Lit images (front lit images do not require LEDs and are closer to traditional printed images). Use your same transmissivity and it will be properly adjusted by the color model to still work.
These are different images, but similar content. Backlight is Warm White (2700K) LED Standard Lightbulb 60w equivalent 
Hard to photograph well, these images look great at a standard viewing distance. Awareness and modeling of the temperature of various white lights for backlighting and a variety of colored LED simulation options.
GPU based STL Generation up to 300x300mm with fixed aspect ratio. A 6 year-old laptop with a barely-there GPU works though it is slow. A 5 year-old desktop GPU works well.
Color Sliders that let you easily adjust and see results in real-time of different color and layer combinations.
Multiple Brightness modifiers to support a wide variety of images.
Multiple methods of calculating the base brightness/luminance including blended modes.
Standard detail/min depth/max depth options.
Drag-and-Drop support for JPEG, PNG, and WEBP image sources.
There are some edge cases here that don’t work properly, generally an image conversion will fix this, but I would like to fix this to support a wide array of image types.
Project saving and export to STL. Upon reload, all relevant sliders, colors, checkboxes, sliders, and selections are properly applied.
Loading of your default settings on startup so that you do not have to pick your most common colors and transmissivities each time to start up.
Would like to add different defaults for Front-lit and back-lit or an easier way to swap between them. This is likely to occur prior to release.
Ability to re-sort your sliders to be in lowest to highest order.
Lit vs Slicer display (click the mouse wheel to momentarily switch views)
Mouse wheel slider adjustment for fine control.
A somewhat janky method of doing automatic cutouts of Lithophanes and Front Lit Images.
I was still working on the color model here for front lit, but the general idea of automatically cutting out an image surrounded by max/min intensity worked perfectly.
What Needs to be Done
Add a “Filament Library” that allows you to save your filaments and choose them instead of colors with unset transmissivity values. This is a simple JSON format that should be easy to share.
A feature not scheduled prior to release is a method of importing a calibrated image of the filament swatch and having it auto-populate.
DELAYED - Support 3mf output to pre-populate the filament swap heights. This has been the active project, but unless I can make some more progress soon, I am likely to punt this until later as it’s just a nice to have. (I thought it was going to be super easy, barely an inconvenience).
DONE - Image area resizing. I shifted all the components to being dockable (I’d also like to save the dock configuration DONE), but given different monitor scalings in Windows (the current target platform) the window needs to resize and it does not currently do this. Most of the dockable areas don’t make sense to resize, but the main image/model viewer does make sense and should allow for a better user experience.
DONE (Still keeping an eye on this it can be complicated) - Account for the base layer height. With layer heights commonly at 0.08 or 0.12mm, it is often advisable to make the first layer a multiple of the layer height for ease of printing - 0.24 is a good start, but that means it should be impossible to set a layer slider to less than the base layer height (0 or off is acceptable) and the layer swap counter should properly reflect the correct layer whether your base is 1x, 2x, or 5x the primary layer height.
Non-multiples are unsupported in the color model at the moment so will not be allowed in the UI. (Need to add validation)
DONE - Grouping the input image, with the project file so that it is less likely to be deleted and be unusable in the future.
DONE (currently only the active profile is saved) - The option to save and restore slider level automatically on a per Litho type (Front or Back lit) and per Luminosity Method or Brightness Compensation basis so that it is easier to compare optimal outcomes between different options.
License keys and distribution platform. If anyone has suggestions on the latter, I would really appreciate some feedback in the comments. I am fairly certain I know how to implement the license keys properly.
Is That It?
This is the pre-release roadmap. I already have a second roadmap firming up of new features that I would like to add, but they are more in depth and more complicated than I would like to include for this release which already provides a LOT of control over the process.
Timeframe
It seems reasonable to me that most of the outstanding features will be implemented (likely with bugs that need testing) or pushed to a post-release timeline by the end of April. Obviously I’d love to get it done before then, but the reality is that this is unlikely to happen given I am a one man team working around my other commitments.
Price
I’m still looking at $10-20 and thinking that early adopters will be $10 and once I’m more tested and feature complete, the price will move up toward the $20 price point.
I have a lot of other things to say, but they aren’t really in the scope of this update so I will save them for another time. That being said, if you know anyone else who might be interested in this software in the future please share with them!