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.

Flocking the trees for the Ouachita area

Last post I started getting a batch of trees pulled out and started pruning them.  

The past few times I made a batch of trees, I used a Tea Pot to steam some of the more curved trees, which seemed to work very well.  I held the bent trunks in front of the steam for a few minutes then stretched them tight or held them flat on the counter top to let them cool.  This seemed to work to keep them straight.

The internet seems divided on what to use on Super Trees.

Some say to use Glycerin, some say to use Matte Medium, while others say they don't use anything but an adhesive to hold the leaves on, which should be enough.

I've used the Matte Medium before and it seems to work just fine, however, I did not use it to attach the foliage while it's still wet. I used cheap hair spray for the foliage, then for the additional layers/colors, I continued to use hair spray.

I'm curious to see how the Glycerin will work?

I know I saved the bath in a gallon milk jug when I got done with it.

The Matte Medium I also saved but between times of needing it, it had separated and it didn't want to re-mix very well, it was kind of a jelly mess. I even added more water, but it didn't seem to help.

I think the glycerin recipe can be rewarmed if needed and reused? We'll see how that goes.

Here's the recipe I used:

4 oz of glycerin
8 oz of 70% alcohol
1 qt of water.

Then bring the mix to boil for a few minutes to get it thoroughly mixed.  

I let it cool off and soaked a batch of trees for two minutes and laid them out to dry overnight.

The next evening the trees seemed to be very springy compared to what they were like right out of the box.  I should say that this box of trees are a little over 8 years old. 

Raw tree on the left, painted in the middle and flocked on the right.

 

Trees along the river

My next project will be tree building, I need to get the shoreline around the Ouachita river covered before the OS Weekend at the end of next month, I think I have enough time if things go right.

Last night I dug out a bunch of Super Trees from my stash and started picking them apart into usable trees.  

Along with the few I have left over from making them for Ruston a few months ago, I think this should be enough?

Let the fun begin...

Floral foam river banks

After a little head scratching and some test fitting, I got the ceiling tile and beadboard foam removed and replaced it with the floral foam bricks.  I glued the bricks in with white glue on the bottoms and where they touch the remaining ceiling tile.

Once dry I'll start the carving process.  I extended the foam out past the abutments just a bit so that I have enough to work with as I slowly carve it back. Most of the bank will be beveled back without much detail as the biggest share of it I envision being covered completely by vegetation.

I also used lightweight spackling to fill in a seam and any irregularities on the plywood then got it sanded smooth. 

Target: The Ouachita River Bridges

I ran a couple of more sessions the last couple of weekends and I feel like things are running smooth enough with JMRI and trackwork that I think it's time to switch gears and start adding some more eye candy to the layout.  I'd like to get this done by this October for the OS Omaha weekend.

In December of 2016 I started reworking the straight track between Calion and El Dorado.  I'd always planned to have a river in this location.  The first thing I did was to reposition the main line to give it a nice little curve and then made plans for a bridge, well two bridges.

Today this is where it stands, and has been standing here since January 2, 2017.  It's been in this state of construction for 8 years now, I think it's stood the test of time.

The other day while staring at it, trying to figure out how to blend the river into the backdrop, the light bulb started to glow.  Instead of blending into the backdrop, why not put a bend in the river and make the shoreline sit against the backdrop?  Then I could hide the river with lots of trees.

After a bit I realized that I had seen this done before recently on a layout that I enjoy following.  The only thing different, that guy hid the bend in the river not only by trees, but with a large building, which I might be able to do as well?  If it does not hide the river completely, at least it'll serve as a distraction for the eyes. 

I'll cut out more foam and ceiling tile behind the truss bridge so the river bends to the right.  I can then go back and add more base along the backdrop.  The base is easy enough to cut out and reshape, but I think I'll use more of the dry floral foam blocks?  It's easy to cut and shape and unlike plaster or lightweight spackling, the foam makes it easy to insert trees into it. 

The river itself should be just about as easy to do, though I'm not sure if I'll pour a thin layer like the bog or if I'll just paint it and apply couple of layers of Gloss Mod Podge?  Here's what I'm shooting for the overall look.

A slow moving, muddy river.  The river banks will be easy, just cover them with heavy foliage and lots of trees...... right down to the banks.

  

Tree line

Got the tree line painted tonight, now I can start working on the base scenery.