Convert pgm to otb

What is the difference between .pgm and .otb?

Description: A PGM file is a grayscale image file saved in the portable gray map (PGM) format and encoded with one or two bytes (8 or 16 bits) per pixel. It contains header information and a grid of numbers that represent different shades of gray from black (0) to white (up to 65,536). PGM files are typically stored in ASCII text format, but also have a binary representation.; The OTB (Nokia Over The Air Bitmap Image) file format is a type of image file developed for use on Nokia mobile devices. These files are specifically optimized for efficient transmission and display on Nokia phones, particularly older models. The OTB format is designed to be compact to facilitate over-the-air (OTA) transmission, which was an essential feature in the era of limited bandwidth and data transfer capabilities. The format supports monochrome graphics, making it suitable for simple images like icons and logos.