Convert APNG (Animated PNG) to PGM

Animated Portable Network Graphics (APNG) is an extension of the Portable Network Graphics (PNG) format designed to support animated images. Introduced in 2004, APNG allows for animated sequences while retaining backward compatibility with non-animated PNG files. This format is utilized for its lossless compression, making it ideal for web graphics where image quality is paramount. APNG files are widely used for animated icons, logos, and other elements that benefit from high-quality animations without the artifacts common in GIF files. Its concise, efficient structure makes it a preferred choice among developers and designers focused on optimizing web performance.

The Portable Graymap (PGM) file extension, originating in the late 1980s as part of the Netpbm project, stands for "Portable Gray Map". It serves as a simple, versatile format for grayscale images, enabling easy reading and writing by various programs. Due to its straightforward structure and plain text encoding, it's often used in academic and research settings where ease of parsing and accessibility are crucial. PGM files store grayscale images in a compact, efficient manner, making them an essential tool for image processing tasks.