Maintenance update

Maintenance update following internal changes (sources more PEP-compliant etc.)

Major update

Substantial I/O change, performance improvement.

Major changes

Main programs changed, GUI and command line versions merged in one file per each method (see readme for more information); includes rewritten to improve speed.

pHYs - print size fix

New behaviour dictated: for PNG files processed with Scale2x print resolution is doubled, with Scale3x - tripled, therefore print size (in millimeters) remains the same. If pHYs chunk in original PNG is absent, 96 ppi is assumed as source resolution since a lot of word processor\page layout software assumes similarly.

2024.02.21 - UI update

Added some progress indicators to GUI, useful when upscaling big files, especially in batch mode.
Some readability improvements on code, especially includes.

2024.02.18 - First release

First release of PNG rescaling Scale2x and Scale3x utilities, including batch rescaling programs. Seem to be useful for improving low resolution scans before OCR. Release include compiled Windows .exe programs - batch rescaling, selected file GUI, and command-line (CLI).