CONVERT
ICO → PNM
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Fast, secure ICO to PNM conversion. No registration required.
ICO is the Windows icon container with multiple resolutions packed into one file. Reaching a PNM from there is one hop. Need a PNM for a CMS, a chat message or an email client that politely refuses ICO? This tool re-encodes your image in the background and returns a drop-in PNM replacement. No registration, no watermark, no visual change beyond what the PNM encoder itself introduces. Keep in mind ICO is the Windows icon container with multiple resolutions packed into one file. And remember that PNM is a raster image format with its own balance of compression, colour depth, and software support.
ICO Icon
Source formatICO is the icon file format used for favicons and Windows application icons. A single ICO file can contain multiple image sizes and color depths for different display contexts.
Portable Anymap
Target formatPNM (Portable Anymap) is a family of simple image formats comprising PBM, PGM, and PPM. These formats store pixel data in straightforward ASCII or binary layouts, making them easy to generate and parse programmatically.
Why convert ICO to PNM
Converting keeps the picture recognisable end-to-end while changing the container that ships it. PNM typically wins on one of three fronts: broader software support, smaller files for the same visual quality, or features like transparency that ICO cannot express. The conversion itself is fast because both sides are raster formats.
HOW TO CONVERT
ICO → PNM
Upload your ICO
Start by dropping the ICO onto the uploader. Files up to 100 MB go through on the free tier without registration.
Conversion happens server-side
Our imagemagick-based pipeline reads the ICO pixel grid, preserves resolution and colour profile, and encodes a clean PNM.
Grab the result
A download button appears as soon as the PNM is ready. Save locally or share the short-lived URL.
Common Use Cases
Cross-platform previews
Windows, macOS and Linux file browsers all render PNM thumbnails; ICO support varies by OS version.
Mobile galleries
iOS Photos, Google Photos and Samsung Gallery index PNM instantly — ICO sometimes falls back to a generic file icon.
Stock photography uploads
Shutterstock, Adobe Stock and similar marketplaces require PNM in their contributor guidelines.
Archive migration
Converting legacy ICO archives to PNM future-proofs the collection against declining codec support.
ICO vs PNM — Strengths and limitations
What each format does best, and where it falls short.
ICO Strengths
- Multi-resolution: one file, many sizes, OS picks the right one.
- Universal favicon support in every browser since IE5.
- Supports transparency (1-bit since 1985, full alpha since XP).
- Tiny file size — an entire favicon pack typically fits in under 15 KB.
- No licensing or patent concerns — fully in the public domain spec-wise.
Limitations
- Cannot compress continuous-tone images efficiently — use PNG or WebP for photos.
- Format is essentially frozen in 1999 — no HDR, no wide gamut, no modern features.
- Maximum image dimension is 256×256 px (inside an ICO container).
PNM Strengths
- Stupidly simple — a 50-line parser handles every variant.
- ASCII variant is human-readable and diff-able.
- Universal Unix tooling support.
- 40+ years of stability.
- Wildcard extension covers three related formats.
Limitations
- No compression — files are huge.
- No color profile, metadata, or transparency.
- Strictly a pipeline intermediate, not a delivery format.
ICO vs PNM — Technical specifications
Side-by-side comparison of the technical details.
ICO
- MIME type
- image/vnd.microsoft.icon
- Max resolutions per file
- 65 535 images
- Max single image size
- 256×256 px
- Color depths
- 1, 4, 8, 24, 32 bits per pixel
- Compression
- Uncompressed bitmap or embedded PNG (Vista+)
PNM
- MIME type
- image/x-portable-anymap
- Extension
- .pnm (umbrella), .pbm, .pgm, .ppm
- Variants
- P1-P6 (ASCII or binary × bitmap/graymap/pixmap)
- Toolkit
- Netpbm
- Creator
- Jef Poskanzer (1988)
| Specification | ICO | PNM |
|---|---|---|
| MIME type | image/vnd.microsoft.icon | image/x-portable-anymap |
| Max resolutions per file | 65 535 images | — |
| Max single image size | 256×256 px | — |
| Color depths | 1, 4, 8, 24, 32 bits per pixel | — |
| Compression | Uncompressed bitmap or embedded PNG (Vista+) | — |
| Extension | — | .pnm (umbrella), .pbm, .pgm, .ppm |
| Variants | — | P1-P6 (ASCII or binary × bitmap/graymap/pixmap) |
| Toolkit | — | Netpbm |
| Creator | — | Jef Poskanzer (1988) |
ICO vs PNM — Typical file sizes
Approximate file sizes for common scenarios.
ICO
- Classic favicon (16×16 only) < 2 KB
- Multi-size favicon pack (16/32/48/256) 5-15 KB
- Full Windows app icon set 20-100 KB
PNM
- 512×512 grayscale (binary) ~256 KB
- 1920×1080 RGB (binary) ~6 MB
Quality & Compatibility
Converting keeps resolution, aspect ratio and colour profile identical to the source. Metadata (EXIF, XMP) transfers where PNM supports it; otherwise it is dropped. If the ICO contained an alpha channel and PNM does not support transparency, the background is flattened to white by default.
Tips for Best Results
- When uploading to Retina / high-DPI contexts, render the PNM at 2× the CSS pixel size; the crispness gap over 1× is noticeable on modern screens.
- Strip EXIF metadata from the PNM before publishing if the ICO came from a phone camera — it often contains GPS coordinates and device IDs.
- If the ICO is a screenshot of text or UI, prefer a lossless PNM target to avoid the JPEG-style ringing around glyph edges.
Frequently Asked Questions
It depends on the codecs involved. If both ICO and PNM are lossy, the pixels are re-encoded and a small amount of detail is discarded — invisible at default quality settings on photographs. If PNM is lossless (PNG, TIFF, BMP) the output keeps every pixel of the decoded ICO exactly, but cannot recover detail that ICO had already compressed away.
Often yes, especially when PNM is lossless. ICO tuned for efficient web delivery will usually produce smaller files than PNM's default settings. If file size matters, drop the quality in Advanced or pick a more compressed target format instead.
KaijuConverter uploads over HTTPS, processes the image in an isolated container and deletes both the source and the output within two hours. No account is required, file contents are never logged, and we do not use uploads to train any model. For confidential material, the paid plan includes a data-processing agreement.
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