ICO vs JP2 — Differences, File Size & When to Use Each

Q: What is an ICO file?

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.

Q: How do I open an ICO file?

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.

Q: How do I convert PNG to ICO?

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.

Q: What size should a favicon.ico be?

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.

Q: ICO vs PNG for web icons: which?

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 tags in HTML.

ICO vs JP2

Um comparativo detalhado de ICO Icon e JPEG 2000 Image — tamanho de arquivo, qualidade, compatibilidade e qual escolher de acordo com seu fluxo de trabalho.

Converter JP2 → ICO

ICO

ICO Icon

Raster & Vector Images

ICO 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.

Sobre os arquivos ICO

JP2

JPEG 2000 Image

Raster & Vector Images

JPEG 2000 offers wavelet-based compression with both lossy and lossless modes. It is used in digital cinema (DCI), medical imaging, and geospatial applications but has minimal web browser support.

Sobre os arquivos JP2

Comparativo de vantagens

ICO Vantagens

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.

JP2 Vantagens

20-30% smaller than JPEG at equivalent quality.
Single format for lossy and lossless — one encoder, two modes.
Multi-resolution: decode a thumbnail from the same file as the full image.
Mandatory format for cinema (DCP), medical imaging (DICOM), and national archives.
Supports 16-bit depth and wide gamut.

Limitações

ICO Limitações

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.

JP2 Limitações

Zero browser support — web publishers cannot use JP2.
Encoding is CPU-expensive.
Consumer tooling is rare.
Patent licensing history scared away early adopters.
Largely supplanted by AVIF and JPEG XL in the modern-replacement race.

Especificações técnicas

Especificação	ICO	JP2
MIME type	image/vnd.microsoft.icon	image/jp2
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+)	Discrete wavelet transform (DWT) with arithmetic coding
Extensions	—	.jp2, .j2k, .jpf, .jpx
Standard	—	ISO/IEC 15444 (Parts 1-18)
Bit depth	—	Up to 16-bit per channel

Tamanhos típicos de arquivo

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

JP2

Web photo (lossy) 150-400 KB
Scanned manuscript (lossless) 5-30 MB
4K DCP cinema frame ~5 MB

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Perguntas frequentes

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.