On 10/03/2024 03:48, jeremy ardley wrote:
Standard thermal label printers are 203DPI (8 dots per mm).
Thanks, this number suits better to my expectation. I just trusted hw earlier.
I have asked the postal service to generate labels at 203dpi which will print just fine at 600 dpi and so work with laser and thermal printers, but they will not cooperate.
Is the QR image a raster one? I am unsure concerning its printer dots per QR pixel ratio. Let's take e.g. 4 as a value inconvenient for direct scaling from 300dpi to 203dpi. I expect that upscaling it by 3 and downscaling the result by 4 with disabled smoothing (e.g. using splines) should generate an image that is 1.5% larger than the one suitable for 203dpi. So setting 98.5% scaling for printer should allow to achieve sharp QR image without re-encoding QR.
You may try to find rational approximation for (4*208)/300 better than 4/3 (or for actual QR pixel size).