http://bwns.be/jim/ecvc-repackage/
A small tool that you can use to repackage your European COVID vaccination certificate. You can change the QR error correction factor, which can reduce the size of the QR code. Additionally, the packed data is recompressed using zopfli, typically yielding better compression rates than typical zlib compression (while being backwards compatible with zlib).
tl;dr: You can make your qr-code smaller (less dense).
Decode your certificate with any qr-code decoder and copy the data in the input form above. I was too lazy to add code to import qr-code images (you can only check so many libraries for hidden backdoors).
No, everything happens inside the browser using JavaScript and WebAssembly (for zopfli). But don't trust me, if you want to be sure disable internet while using the page (or block all subsequent requests from this domain after loading the page in developer tools).
I wanted to stick my COVID certificate on my university card so that I didn't need to use my phone to enter the restaurant of the university. However, the error correction on the default European certificate card is extremely high, which means that the individual pixels are very small when printed to fit my card. The Belgian CovidScan application doesn't like this, so I tried repacking the QR-code to see if I could change the error correction rate. This proved to be successful, but I wanted to see if I could go further and reduce the size of the compressed zlib data. I discovered zopfli and thus this application was born :)
The excellent QR-code library from Project Nayuki (https://www.nayuki.io/page/qr-code-generator-library), a random base45 decoding library found at lovasoa/base45-ts, pako, a high speed zlib port (nodeca/pako), https://github.com/gfx/universal-zopfli-js, a WebAssembly build of google/zopfli.