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I thought I document the process I figured out for myself of how to best approach doing watercolor painting based on digital sketches with the help of a DLP projector.

Background

I have been working on my painting skills for some years now and ended up in a on/off relationship with watercolor. Did not like acrylpainting, did a limited amount of gouache painting and kept coming back to watercolor even though it made me quite mad at times.

One of the things I was very dissatisfied with was using pencil to sketch out my paintings. It was always a struggle to draw faint enough so that the markings wouldn’t bother me in the final result and also a lot of losing shapes and lines in the heat of things.

While I made my peace with watercolor not always coming out like you want to, it kept bothering me how I would also lose my sketch and had to start over from zero to redo a painting.

DLP-Projector

I discovered DLP (Digital Light Processing) projectors by accident in a youtube video. I wasn’t even aware that the technology existed and that it allows for devices that are very different from your clunky old projectors. The “digital micro mirrors” basically allow for fine-controlled projection that isn’t straight forward.

I ended up buying a “EKASN Mini Smart DLP Projector” which no longer seems to be avaible, which sadly often seems to happen, but I imagine that other devices based on the same DLP chips will work very similar.

My projector runs “Android TV” as operating system which offers a lot of options of how to get images on there, but in the end, the installed File explorer thing comes with a Browser based upload thing (with Chinese UI 🤣) that seems to work best.

Starting a Painting

When I want to paint a painting, it starts with the paper I want to paint on. I usually work with watercolor paper blocks, so I chose the texture and size I want.

So let’s say I use Arches cotton paper, 31cm x 23cm. That means I create a new image that has a nice big resolution that works well on my Cintiq. Usually I chose the larger dimension to be 1920 which is the FullHD width and also a good fit for the height on my screen with enough room on the left and right for palettes, toolbars and references and whatnot.

So for the Arches 31cm x 23cm in landscape format and a target width of 1920 pixel, we need a height of 1424px (1920 x 23 / 31). I usually tape my paintings to have a nice white border in the end, so I include that in my template and use the area for some simple projection markers.

Here I created a border for the painter’s tape I have which is 18mm wide. You can download the empty template in OpenRaster-format below. (I use OpenRaster so I can have a multi-layer image I can open in Krita as well as Gimp).

The example above has multiple sketch layers. For one the handdrawn sketch and then a layer with black at a low opacity where I planned the shadows for the scene.

When I do the shadows, I duplicate the shadows and use an edge filter to get the outlines for it, too. Then I save two different images. One just with the lines and one with the shadow layer.

Preparation

Once I’m ready to start projecting, I save the projection images as PNG and run them through my preparation script.

#!/bin/bash

if [ -z $1 ] || [ -z $2 ]; then
        echo "Usage: c900prepare <image> <output>"
        exit 1
fi

# scale to c900 native resolution, rotated if needed
convert $1 -rotate "90<" -scale 1280x720\! $2Code language: PHP (php)

This is a linux shell script using ImageMagick and the last line is the most important $1 is the input file here and $2 the output file.

If this all sounds to complicated for you, the basic idea of the command is that I scale down my projection images to the exact native resolution of the projector (1280×720). This scaling disregards the correct aspect ratio of the image and stretches it to fit. What the script also does is take care of the orientation. 1280×720 is obviously landscape format, but sometimes I want to project in portrait format that is higher than its wide. So this command rotates the image by 90 degrees if it is portrait format so that the former top of the image is to right which seems to be the easiest way to setup my projection equipment.

Setting up the projection

So I have my table top easel where I can adjust the angle, sometimes I work at an angle like this for controlled washes, sometimes I work flat. I bought these photography arms that I assembled to this McGyver-ed configuration. This way I can adjust my arms in all kinds of directions. I usually try have the projector a good length in front of me so that it doesn’t project downwards and I am always shadowing what I paint. By projecting from the front the shadows fall towards me and the area under my brush is as illuminated as possible.

As you can see the projection comes from quite an angle at the paper, but it still perfectly hits the square of it. The manual projection adjustment allows each corner of the projection to be moved pixel by pixel until it matches the canvas.

The projector position should be made to fit the paper as good as possible. Reset the projection if necessary and put the projector at a distance where all four corners of the paper are in the light. Make sure the image is centered on the paper.

Now use the projection adjustment to move the corners inwards until they match the paper. I usually adjust it so that the light creates a bit of shine outside of the paper and then adjust that so that the shine has the same brightness along the whole edge of the paper. This seems to be more precise than trying to have the slightly fuzzy projection edge match the paper edge (Arches paper also has a black binding which makes that even more difficult).

This process fixes the disregard of the aspect ratio in my preparation step as it stretches the projectors native resolution back to the aspect ratio of the paper I started out with. If I did my math right, the lines I draw around the image in my template match exactly with the inner border of my tape and the little projection marker boxes fill out the corners.

Conclusion

I really like to work this way, it allows me to work digitally on my sketches and move things around, scale them, copy and paste parts, whatever, the full digital convenience. If I fail to paint how I want, I can always restart with the same projection sketch. For some of my paintings sometimes I do three or four attempts.

It is no silver bullet. The projected lines are pretty strong if maybe a bit low resolution sometimes. It is still possible to get lost. Especially when I’ve already laid down the darker paint it can be hard to see the lines. I often flip back and forth between the projection image and an empty white image which can help to find lost lines. At some point it is just best to just let go of the projection and just work with the painting. I also have another android tablet for reference images. Mostly for color reference, but I also copy the projection image over to keep working with it while not actually projecting.

References

• Arches 31cm x 23cm template – four layers: border, thirds grid, sketch layer and white background
• ImageMagick – software I use for automation