ICO vs PCX
A detailed comparison of ICO Icon and PCX Image — file size, quality, compatibility, and which format to choose for your workflow.
ICO Icon
Raster & Vector ImagesICO 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.
About ICO filesPCX Image
Raster & Vector ImagesPCX (PiCture eXchange) is a legacy raster image format created by ZSoft for their PC Paintbrush program. It was one of the first widely supported image formats on IBM PC compatibles and uses simple run-length encoding compression.
About PCX filesStrengths Comparison
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.
PCX Strengths
- Simple format — easy to parse in any language.
- RLE compression keeps flat-color images compact.
- Historic archive format for 1985-1995 PC art.
- Stable since 1985 with no breaking changes.
Limitations
ICO 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).
- Editing requires specialized tools — most image editors treat it as a curiosity.
PCX Limitations
- Legacy — no new content created as PCX in 2026.
- Inefficient for photographs (RLE is wrong algorithm).
- Limited to 24-bit color depth.
- Web browsers do not display PCX.
Technical Specifications
| Specification | ICO | PCX |
|---|---|---|
| MIME type | image/vnd.microsoft.icon | image/x-pcx |
| 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+) | Run-Length Encoding (RLE) |
| Extension | — | .pcx |
| Header | — | 128 bytes fixed |
| Creator | — | ZSoft Corporation (1985) |
Typical File Sizes
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
PCX
- Simple clipart 2-40 KB
- VGA-era screenshot (320×200) 30-80 KB
- Scanned page 200 KB - 2 MB
Ready to convert?
Convert between ICO and PCX online, free, and without installing anything. Encrypted upload, automatic deletion after 2 hours.
Frequently Asked Questions
ICO (Icon) is Microsoft's 1985 multi-resolution icon format, originally shipped with Windows 1.0. A single .ico file holds multiple sizes (16×16, 32×32, 48×48, 256×256) so the OS can pick the best one for the current display context. Since 1999, every website uses a favicon.ico to show its icon in browser tabs.
On Windows, ICO files open natively in File Explorer and Photos. On macOS, Preview handles basic display. For editing, use GIMP (free), Photoshop with a plugin, or dedicated icon editors like IcoFX.
Use the PNG-to-ICO converter on KaijuConverter — upload a PNG (ideally square, at least 256×256) and download a multi-resolution ICO with all standard favicon sizes embedded.
A complete favicon pack includes 16×16, 32×32, 48×48, and 256×256 px variants all in one ICO file. The total file size is typically 5-15 KB. Browsers automatically pick the right size for tabs, bookmarks, and desktop shortcuts.
ICO for /favicon.ico (every browser requests this URL automatically). PNG for everywhere else — social media profile images, in-page icons, app logos. Modern favicon best practice includes both an .ico at the root and multiple .png sizes referenced via <link> tags in HTML.
Yes. Every browser still requests /favicon.ico on every domain as its first icon fallback. Modern sites typically provide both favicon.ico and higher-quality SVG or PNG icons via <link rel="icon"> tags — browsers pick the best match.