Creating a Backdrop Tree Line with Gemini AI

Over the past year or so, I have seen model railroaders add snow effects to photos of their layouts using AI. Modeling a Southern local, I preferred rain and a stormy atmosphere over snow. I decided to experiment with Gemini AI to generate custom imagery for my layout like others have done.

Crafting effective prompts is key. Even with detailed phrasing, the initial output may not match your exact expectations. For example, when attempting to show locomotive headlight beams shooting forward, several generations produced beams pointing skyward from the cab windows. With persistent adjustments to the prompts, I achieved the desired result.

Designing Backdrop Buildings

When planning the backdrop for the yard, I wanted a continuous line of trees spanning its full length. Satellite imagery of Biddle Yard in Little Rock, Arkansas, confirmed a dense tree line on the north side of the yard, separating it from the city.

Rather than hand-painting the scenery, I used Gemini to generate backdrop structures and foliage, intending to show select building tops peeking over the tree line.

I prompted Gemini to generate a large, three-story metal-skinned industrial building featuring a two-tone tan exterior with lighter tan on top.

Initial attempts produced three-quarter angled views from an elevated perspective. To make the image suitable for a flat backdrop, I refined the prompt to request an elevation view showing only the front face of the building without perspective, roof lines, or side walls.

Then to visualize the final composition before painting, I instructed Gemini to add a row of foliage in front of the structure.

Not quite what I wanted.

I then requested the removal of overhanging branches above the roofline, leaving only a low tree line covering the lower portion of the building. Interestingly, Gemini added rooftop HVAC units during this pass without explicit prompting.  Now we’re getting somewhere!  It was about that time that it occurred to me, why not just have Gemini create a tree line to print and paste to the backdrop instead of trying to play Bob Ross?

Generating the Tree Line

At this stage, I realized I could generate printable tree line images directly rather than painting them by hand.  After experimenting with various prompts requesting photorealistic tree lines, Gemini produced this usable image.

Planning and Printing Considerations

Several technical challenges required consideration during the planning phase:

Sky gaps: Gaps within the foliage needed to display a blue sky tone matching the painted backdrop rather than a stark white background.

Foliage trimming: Cutting out intricate treetops across long sections can be labor-intensive.

Pattern variation: To avoid repetitive patterns across a 20-foot backdrop, multiple distinct image segments were necessary.

Production method: I evaluated printing custom banners at a commercial print shop versus printing multiple smaller sheets at home on standard 11.5-inch paper. Printing locally provided greater flexibility for variation and adjustments at a comparable cost.

Image Editing and Color Matching

To streamline preparation and installation, I used the following workflow:

Sky Background Alignment: I re-imported the tree line into Gemini and requested a solid blue background. After lightening the tone by 10%, the color matched the painted blue backdrop on the layout pretty close.

Resolution Upscaling: Downloaded PNG files were upscaled to approximately 1600 pixels wide, which provided sufficient resolution for N scale modeling.  I think 1600 was the maximum size with the free version?

Background Ink Reduction: I converted the PNG files to JPG format and used the eraser tool in MS Paint to clear out large areas of blue sky, reducing ink consumption during printing.

Trimming and Blending: I roughly cut along the treetop perimeter. Any remaining blue paper margins were later blended into the painted sky using a stippling technique with backdrop paint.

Color Correction: Because printed outputs ran darker than displayed on screen, I adjusted exposure, sharpness, and green hues using Luminar4 and it's photo editing capabilities prior to final printing.

Media Selection and Layout Setup

Using standard paper can cause ink absorption, producing dull images. I opted for Matte photo paper, which maintains crisp edges. To optimize print speed and ink usage, I configured the printer to standard quality on plain paper settings while feeding Matte photo paper, yielding sharp results without excess ink laydown.

Others weren’t kidding, using the photo paper rather than plain copy paper looked much better.

I arranged the images in CorelDraw, scaling them in landscape orientation to a height of no more than 4.5" in height. This setup allowed two tree line prints per sheet.

Assembly and Installation

I followed these steps to prepare and mount the printed tree line sections:

1. Trimming and Mating Edges: Square the side and bottom edges using a paper trimmer to ensure clean splices. Trim the tops along the foliage outline.

2. Edge Coloring: Run black, green, or brown markers along cut paper edges to eliminate visible white paper borders.

3. Clear Coating: Apply two light coats of Krylon Acrylic Matte finish to protect the printed ink from moisture during subsequent scenery work.

4. Adhesive Application: Brush full-strength Matte Medium onto the back of each print. Matte Medium provides sufficient working time for position adjustments and dries clear. I thought about using a spray adhesive, but I read where that stuff will break down over time. allowing the images to curl.

Boomer suggested using Matte Medium as the adhesive. It dries completely clear and easy to clean up and paint over if needed.

5. Mounting: Press the print onto the backdrop. Use a 4-inch foam roller and a glass jar to burnish the surface, smooth out imperfections, and press out excess glue. Clean up the squeeze-out immediately with a damp sponge. The Matte Medium doesn't dry on contact. It takes a little bit of time to set up, but that also allows you a short window where you can make slight adjustments if needed.

6. Final Blending: Allow the adhesive to dry thoroughly. Stipple matching sky paint over remaining paper margins and white paint for cloud highlights to blend the prints seamlessly into the backdrop.

Layering Trees Over Structures

For sections featuring buildings situated behind foliage, generate the tree line as a transparent PNG file instead of a JPG file. Removing the background color allows underlying structures to show naturally through gaps in the branches.

Now I know there are probably better ways to do this, but if so, I’m unfamiliar with how that works.  I’m using methods that I know.

Tree line created by Gemini AI

I think I'm going to like doing this?  They actually came out better than I would have thought, the actual printing that is.

In a way, they kind of look a little overpowering, but I think it's because I'm so use to seeing just a blue backdrop for several years?

I'll try to explain the process of how I created the trees, from conception and design to the actual gluing onto the backdrop in the next post.

In the meantime here a few shots of how they turned out.  The first shot is the left end of the yard where it joins the main layout.

There are seven unique 11-1/4" wide sections that make up the long backdrop.  I used 2 more 11-1/4" sections for the angled backdrop (with the water tower), of which one of them I trimmed to fit.

The left end.

The right end.

The angled section on the right end.

To clarify, the building and water tower were both embedded into each print with the tree line that they reside behind as a single image.  

I couldn't see the forest due to the trees

How does that old saying go? "One step forward, two steps back."

That is exactly how I'm feeling right now, but I think it will be worth the trouble in the end. After painting the trees at the entrance of the yard, I let them sit for a few days to see if I liked the look. While I was happy with what I had created, something was still bothering me. A few nights later, that "something" finally revealed itself: I wasn't thinking far enough ahead.

When I painted trees on the backdrop around the main layout, I did it so that when I eventually "planted" 3D trees, you wouldn't be able to see a solid blue background through the branches.  

In the following images, you can see that after painting the background trees, I finished the basic ground cover. The actual scenery base comes next (I haven't finished it yet).

 

I did manage to get some trees made and planted behind the Ruston depot scene. As you can see, looking through the 3D trees doesn't reveal a solid blue sky all the way to the ground. In my opinion, this gives the scene much more depth.

So, I decided to continue painting trees across most of the yard’s backdrop, just as I had elsewhere. My plan was to stop the painted trees, add an AI-rendered building at the end, and then start a line of AI-rendered and printed trees. These were meant to extend all the way around the yard's backdrop, with a few breaks here and there.

My thought was to place a printed building partially over the painted trees and partially behind the printed trees, which hopefully would create a forced perspective and add some depth. However, after looking at the building flanked by painted trees on the left and printed trees on the right for several nights, I realized that was exactly what was bothering me. I removed the building before taking this photo, but you can still get the idea.  There was just too much of a difference.

The main issue here was space. Unlike the other parts of the layout where I could plant 3D trees in front of the painted ones, the yard has no room between the rearmost track and the backdrop for physical trees.

This is why I was looking into printing photos of trees and buildings in the first place—I just simply got ahead of myself. I realized I needed to remove the painted trees at the yard entrance. I tried painting over just the trees, but since some of the clouds were behind them, I decided to bite the bullet and entirely repaint that section of the backdrop.

A couple of nights and two coats of blue paint later, the deed was done. Of course, I then spent another night repainting the clouds, but they turned out better—a bit more transparent and fluffier than before.

With that settled and behind me, I focused on the AI tree line. I've played around with 2D drawings and photos before, but I'd never attempted to use them for a backdrop. The idea for the tree line actually came to me while I was experimenting with AI to create backdrop buildings. At one point, I wanted trees in front of the buildings, and I really liked what Gemini produced, even if it was just a visual experiment at the time.  Mind you, this is 100% AI

So I fired up Gemini again and started playing with the command prompts, which really are the key to AI. I asked it to render a tree line for a model train layout and had it add a solid blue sky with no gradient, adjusting the shade several times until it looked right. After tweaking a few specific keywords, it gave me this:

Once I converted it to a JPG, I used an eraser editing tool to remove almost all the blue sky so I wouldn't waste ink during printing.

Unfortunately, I didn't take pictures in the proper sequence because I was so focused on the task at hand. But if you look closely, you can see the printed blue sky is slightly darker than the painted backdrop.

While pondering how to remedy this, I continued to search YouTube videos and found a modeler who had already solved the problem.  Basically, after the glued images were dry, he went back with the same backdrop paint and carefully blended it onto the edges of the images. Voila! Simple and effective.  If you look closely you can see the printed sky in the first image, in the second image the transition is barely noticeable.

  

Trees at the entrance of the yard

With the clouds finished I decided to get on with the trees.

On the left end of the yard where it connects to the layout, there is a 6' section of backdrop that I want to try and transition into the yard.  I started out painting the trees the same way and the same height as they are on the backdrop behind Winnfield.  I painted them about 2/3rds across.  At this point I think I'm going to add my first building then start painting larger trees.  I'm hoping this is going to help show some forced perspective.

This time before painting them, I had the forethought to record the progress unlike last time.

I started the tree line using the dark green that I used when I painted the previous trees, it's basically a Hunter Green and serves only to give me a base to build off of.

The next step was to stipple black paint, which is used to give depth to the trees and act like shadows.

Once this is done and dry, I used two shades of green craft paint.  A Dark Forest Green and a Medium Green.  I mixed a small amount of the Medium green just to lighten the Forest Green up a touch.

This also helps to mute the black so it isn't so stark.  At this point, the shape of the trees are starting to show up.

Next I used straight Medium Green and stippled it over most of the tree shapes, but since I want the sunlight coming from the upper left, I tried to keep most of this color from the middle to left side of each tree.

Now comes the fun part and where the trees start looking like trees.  Using the Medium Green I mixed a small amount of yellow in for a lighter green.  This I tried to keep to the left most side of each tree clump.  This is where the sunlight is starting to hit the leaves, making them a bit more bright.

Finally, I continued to add the Yellow to the green from the previous color.  I didn't want the leaves to look too Yellow, so the previous green gave me a subdued greenish yellow and just enough to highlight the leaves and show a pronounced shape of individual trees.

Too much yellow and the effect will look ruined.  It's hard to tell, but the colors do darken a bit as they dry.  Sometimes it's good to stop and give the colors a chance to dry which tells you if you need more or less color.

With this stage done, I sat the backdrop back into place.  As in the yard, there is no space between the track and backdrop to plant full 3D trees, so I think I'm going to use a small amount of poly fiber covered with some darker ground foam and place it along the backdrop to hopefully hide the line where the backdrop meets the surface. 

Truth be told, the entire painting process only required about an hour of my time.

Clouds over Biddle yard

Clouds were the first thing on the agenda for the backdrop behind Biddle yard.

These were made with an airbrush and stencils, pretty much as I had done on the rest of the layout. Except this time, I used my new Paasche double-action brush. Instead of using the cheap craft paint as I've done previously, I tried something different. After using Tamiya paint on the new tracks at DuBach and liking how it sprayed, I decided to try Tamiya for the clouds. I have to say, it was easy to use, easy to clean up, and had hardly any smell.

Here is what I've been looking for the past several years.

Here are the backdrops sat back into place with the clouds.

I have not painted any clouds on the small angled portion of the backdrop for now as I plan to hang a diagram of the yard on that one.  However, I suppose I could just keep the clouds a bit lower?

The next stage will be printing the buildings and applying them to the backdrop. But first, I'm going to play around with resizing them so they look proportional to the scene.  If I recall correctly, they should be printed around 20% to 30% smaller to give a slight appearance of distance?

Planning the Biddle Yard backdrop

Not much has happened on the layout for the first half of this year.  Mainly due to me jumping feet first into operations and making a lot of small adjustments to JMRI.  As evidence from the last session on May 9th (the previous post), I think I've finally got a good handle on it as it seems to be working pretty much the way I've had it envisioned.  Cars are moving smoothly to all the industries in a fairly random pattern.  I'm also getting a pretty random amount and types of cars moving.  So I feel it's time to get back to the layout.

However I'm finding that I'm struggling trying to find the motivation to work on a few things.  I had planned to paint up four more locos in the Blue and & White scheme and/or start working on another scene on the layout between DuBach and El Dorado, but I just can't find the motivation to start on these projects.

The other night while staging the layout for another op session, I was looking at the yard and all I could see was the 16' long blue backdrop. Ugh!  I got to thinking this might be a fairly easy project to tackle, nothing real fancy just some paint and some backdrop buildings?

The more I thought about it the more I started leaning to picking up more of the 2d printed background buildings like I did from Trackside Flats.

Not 100% sure how I wanted to tackle this as it was going to cost a decent amount for these buildings.  I had a couple choices.  I could buy what I needed from them already printed and mounted on black foam core and mount them to the backdrop.  I could also buy all the buildings on two large sheets, cut them out and mount them myself to foam core or glue them directly to the backdrop?  Or I could buy several premade backdrops, cut out the sky and just glue them to my backdrop.

I had envisions of having buildings running from one end to the other or space them out with some painted trees.   But that would entitle 16' of printed buildings and that could ensure that I'd spend some coin to do this.  Plus not sure how to layout the buildings to make the backdrop look plausible?

Somewhere along the line, a little voice in my head spoke up and told me to go look at the actual location.  Hmmm?  So I jumped on Google Maps and looked up Little Rock, AR.  Snooped around until I found Biddle yard.  It's pretty much intact yet as UP is still using it but the engine facility is pretty much gone, but you can still see the old roundhouse and tracks.

Right away the first thing I noticed was the overall shape of the yard.  If you compare the aerial to a plan of my yard it almost fits perfectly.

Using the engine facility on my yard as an anchor point, I noticed that where I am standing when running the yard, I would be standing where all the trees are located just to the south of the actual yard.  On where the backdrop would be, I noticed another line of trees that separated the yard from the south edge of Little Rock.  I'm sure that back in 1979, those large buildings were not there yet and the tree line was probably thicker?

But this got me thinking and I started using my modelers license.  Instead of lining the entire 16' of backdrop with 2d buildings, why not just use trees, much like I have with the biggest share of the rest of the layout?  But I got to thinking: "Maybe that would not look good as then, no matter where you looked, you'd see a tree line all the way around the layout?"  It might be a bit too much?

Then that little voice spoke up again.

What if I painted a solid (or pretty much a solid) tree line along the backdrop, then add some taller buildings BEHIND the tree line?  The trees would hide a lot of the shorter buildings, but the taller ones could peek above the trees, using less buildings?

I went back to Google Maps and started taking a closer look.  I dropped the little guy onto the highway bridge overlooking the yard.  The first thing I noticed was that large building behind the trees.  Granted, I'm thinking this image was taken in very early Spring as the trees are just starting to leaf out.  But once the leaves totally fill in, it should hide the biggest share of anything to the north of the tree line?  

The first image is a view off the highway looking N/NE, the second image is from the east of the yard looking W/SW.  Those trees are pretty tall?

One can see the building back there in these views.  But once the leaves fill out, you may not be able to see much at all?  So I chewed on this for a while.

The next day at work, my mind started wandering.  Instead of buying a bunch of building flats, I wondered if Google Gemini could lend a hand?  When I got home I sat down and pulled up Gemini and asked it to render me a very large metal sided building about 2 stories tall.  Color it a two tone tan, with the darker color on the bottom half.  After a bit of fiddling it gave me this:

Since I wanted trees in the foreground, I didn't want to use printed trees due to the fact that the blue sky  showing through (if any) would have to match the color on the backdrop.  And I didn't want to go through the images and cut out the areas, so I decided I would paint the trees, much like I have on the rest of the layout.

This beckons back to the old argument of do I use a printed backdrop or a painted backdrop.  Do I want my eyes drawn away from my layout and onto the backdrop, or do I want the backdrop to just be there but not the main focus?

Painting the trees would do two things, I feel it would keep my eyes being drawn to the backdrop and it would also keep the look matching the rest of the backdrop around the layout.  Painting it would be!

Using the image that Gemini gave me of the big building, I asked it to render a line of trees in the foreground, but only about 2/3rds as tall as the building.  Again after a few adjustments to the wording, it gave me this:

The little voice cheered!

Now I had a good visual representation of what I wanted to do, and the way I've painted the previous trees on my backdrop I had a good idea of what I could do.  However I got to thinking, these trees are going to be a little closer than any of the others which meant I was going to have to make them a bit more detailed and I would probably have to trunks to make it look close to the image.  I think I can do this?

I took one of the 2D flats I purchased and decided to sacrifice it for the cause.  Figuring that the paint might soak into the image and ruin it, I sprayed it down with several light coats of a matte finish in a rattle can to hopefully seal it.

If I actually do this, I will NOT apply the images to black foam core, but will instead print the image on cardstock, then glue that to the actual backdrop.

Then I applied a thin coat of dark green that I've used on my "Distant Hills".

Next, I used some latex paint that was close to a tree trunk color and simply sketched in some trunks.

What I didn't take images of was the process of adding the stipple black blotches for shadow and applying the different shades of greens, starting with a darker green then working towards the lighter shades and ending up with an almost yellowish green to represent sunlit leaves.  But you can get a good idea with this image.

Here it's sitting in the yard against the backdrop.  I might have to adjust the height as it might be a little tall?

Now to see if I can bring this idea to fruition.