Filters commonly used to make blueprint effect

Question

I want to create a "blueprint" aesthetic, so I went online and found a website that does a great job but I would like to know HOW it does it. Of course, I don't mean adding the grid or the background blue color, but specifically extracting the outline from an image. Also, I do not have Photoshop and use Gimp or Krita instead, so a general answer might help more. Here's an example:

Original image:

Filtered image obtained from website

I tried a few line detection filters but they do not work quite right. Best I got is Sobel-Feldman which gives me the following:

Which looks great but not so much when the image has a lot of white.

Thanks

Answer 1

Get G'MIC for GIMP (also available for Krita, Photoshop and other image editors). It's available at gmic.eu - install it and restart GIMP. It's a plugin with a collection of over 560 filters. It's very useful if you find GIMP's native filters to be a bit limited. Note: I have no affiliation with the developers of this free plugin.

Open the original colour image, and do to Filters > G'MIC-Qt, and run the Edges filter in the Contours dropdown list, select the Negative Colours option, and hit OK

Do Colors > Brightness and Contrast, and reduce the sliders a bit

Do Colors > Colorize - choose a colour, tweak the sliders as required

With G'MIC it's also possible to apply more than one filter, you can set the Output Mode to New Layers each time you run a filter, and when you hit Apply, it will generate a new layer in GIMP. This can be useful if you want to mix filters. For example there is a Glass Texture filter in G'MIC which could be used to make the texture shown in the example image. Once output to layers, you can adjust the opacity of the texture.

For example

Answer 2

With plain Gimp:

• With the color selector, select each color in turn (except the background), and Select > To path
• One you have them all, open the Paths list, make all the paths visible, right-click, and Merge visible paths
• Add a layer, fill with dark blue
• Add a layer, leave transparent
• Set foreground color to light blue
• Edit > Stroke path in Line mode,with a thin (1px) line width
• Add a layer, leave transparent
• Filters > Render > Pattern > Grid , with a 1px line width (this will use the same color as for the paths)
• If the grid seems a bit too thick, just reduce the opacity of that layer

Some lines can be a bit too thick because they are part of two selections and are stroked twice. This can be fixed by editing the paths (removing anchors anchors) before merging them.

Answer 3

In Photoshop, the following filters are commonly used to create a blueprint effect:

The "Desaturate" filter, which can be found under Image > Adjustments > Desaturate, is used to remove color from an image and create a grayscale blueprint.

The "Halftone Pattern" filter, located under Filter > Pixelate > Halftone Pattern, can be used to create the dot pattern often seen in blueprints.

The "Threshold" filter, found under Image > Adjustments > Threshold, can be used to create a black and white blueprint by converting the image to a high-contrast, binary representation.

The "Posterize" filter, located under Image > Adjustments > Posterize, can be used to reduce the number of colors in an image and create a more stylized blueprint effect.

The "Find edges" filter, located under Filter > Stylize > Find edges, can be used to create a blueprint effect with strong lines and edges.

The "Graphic Pen" filter, located under Filter > Sketch > Graphic Pen, can be used to create a blueprint effect with hand-drawn lines.