Alternative if conversion fails?

PPM (Portable Pixmap) is the colour member of the Netpbm format family (PBM bitmap, PGM greyscale, PPM colour) defined by Jef Poskanzer in 1988 and still the lingua franca of Unix image-processing pipelines. The format is intentionally simple: an ASCII or binary header followed by raw RGB pixel data with no compression. Scientific imaging tools (AstroPy, scikit-image), academic computer-vision research, and command-line glue between ImageMagick, ffmpeg, and dcraw all use PPM as a lossless interchange - the simplest format that everything reads.

Converting PPM to HEIC is the compact-output step at the end of a pipeline: a 4096x4096 8-bit PPM is exactly 48MB of raw bytes, while the same content as high-quality HEIC lands around 2-3MB - half of what a JPG export would weigh - and opens natively on the MacBooks and iPhones where results actually get reviewed. There's a bit-depth bonus too: PPM's 16-bit P6 variant carries scientific dynamic range that an 8-bit JPG export truncates, but HEIC's 10-bit encoding preserves four times the tonal resolution, which visibly reduces banding in stretched astrophotography and microscopy renders.

The workflow fit is natural for anyone gluing tools together: pillow-heif gives Python pipelines direct HEIC output (Image.open('in.ppm').save('out.heic')), and a libheif-enabled ImageMagick does it in one command. Mind the destinations though - journals want figures as TIFF or JPG, LaTeX toolchains have no HEIC support, and web publishing is patchy - so treat HEIC as the review-and-archive copy and pull JPG derivatives for submission artifacts. Linear (unstretched) data should be histogram-stretched before conversion regardless of target format.

Reasons to convert PPM to HEIC usually come down to compatibility, file-size, or specific feature requirements. Common situations:

• An app or platform only accepts HEIC uploads.
• You need a feature unique to HEIC (e.g. transparency, vector scaling, animation, multi-page pages, etc.) that PPM doesn't provide.
• You're optimising file size — modern formats often produce smaller files than the older format you started with.
• You need a single archival format across a project so files behave consistently in the same viewer.

1. Open the PPM → HEIC tool on heic.now.
2. Drag your PPM file onto the drop zone, or click Select files. You can drop a whole folder of files at once.
3. The output is fixed to HEIC. If the format supports extra options (page size, transparency background, quality, EXIF stripping), tweak them in the right-hand panel.
4. Click Convert. The job runs on our server and finishes in a few seconds for typical photos.
5. Download the result. Files stay in storage for 24 hours and are then permanently deleted.

The entire flow is free for the first 10 jobs per day with no signup required. A free account doubles that quota; a premium plan removes the limit entirely.

• 16-bit PPM sources map into HEIC's 10-bit encoding - far less banding than an 8-bit JPG export, though extreme scientific dynamic range still deserves a tone-map first.
• For astrophotography PPM stacks from PixInsight or Siril, apply a histogram stretch before converting - linear data looks black in any viewer regardless of format.
• ASCII (P3) PPM is roughly 3x larger on disk than binary (P6) - both convert identically, but prefer P6 in pipelines for speed.
• In Python, pillow-heif adds direct HEIC saving to Pillow - Image.open('in.ppm').save('out.heic') slots straight into existing scripts.
• Journals and LaTeX toolchains don't take HEIC - keep the HEIC as your compact review archive and export JPG or TIFF for submission figures.