Set image print size and make black and white

This is a note to self for my own calligraphy stuff.

There is sometimes a need to print out templates in actual size. And to save ink when printing, I try to make it as much black and white as possible.

First, to convert to black and white and remove gray background.

In GIMP, under Colors -> Threshold, pull the pointer toward the right until the preview shows a more or less acceptable degree of black and white.

Then, to set the print size. As it is usually necessary to enlarge the image, the first thing is to scale up the image.

Under Image -> Scale Image, scale up the image by two to three times.

Then, set the print size by

Image -> Print Size, defining either the width or the height in mm.

Some final touches may be needed, such as using a brush to remove black spots, or using the fill tool to fill in areas with white color.

Finally, save the image in PDF format so that it can be posterized.

To posterize, install pdfposter using

sudo apt install pdfposter

Then run the following command:

pdfposter -s1 -mA4 input.pdf output.pdf

This will create a PDF file (output.pdf) with the image in several A4 pages (-mA4) with a scaling factor of 1 (-s1). Once it has been printed out, the final step is to paste the pages together.