EXR to ICO Converter

Encoding: the EXR uses none, RLE, ZIP, PIZ, PXR24, B44 or DWA, chosen per file; ICO uses each size stored as a headerless BMP or as a complete PNG, and the download is a multi-size ICO with PNG-compressed icons (16, 32, 48 and 256 px by default).

Bit depth: 16-bit half or 32-bit floating point per channel in the EXR; ICO allows 1 to 32 bits per pixel, set per size, and the ICO written here has 32 bits per pixel. Floating-point values are mapped to 8 bits per channel, and anything brighter than white clips.

Colour: scene-linear RGB, often ACEScg or linear Rec.709 in the EXR; ICO supports RGB or a palette, per image, written here as 8-bit sRGB.

Transparency: the EXR stores it as an A channel stored like any other channel; the ICO keeps it as 8-bit alpha in 32-bit and PNG entries, or a 1-bit mask in old icons.

Other images: the EXR can hold extra channels (depth, normals, render passes) and multiple parts; only the main image is converted.

Metadata: the EXR can carry named header attributes such as chromaticities, timecode and camera data; ICO can carry only a directory of the sizes inside, with no EXIF, but nothing is copied across.

OpenEXR is the high dynamic range format of film visual effects. It stores half or full floating-point channels in linear light, plus any extra render passes, and is the working format of compositing pipelines.

An EXR starts with the magic number 76 2F 31 01 and a version field, then a header of named, typed attributes (channels, compression, dataWindow, displayWindow) and a table of offsets to scanline or tile blocks.

EXR files usually come from 3D renderers and compositing in Nuke, Blender, Houdini, After Effects and DaVinci Resolve.

ICO is a container that bundles several sizes of the same icon (16, 32, 48, 256 px) into one file. It is still the most compatible format for website favicons and Windows app icons.

An ICO starts with a 6-byte ICONDIR (type 1 for icons) and a 16-byte entry per image giving width, height, colour count and offset. Each image is either a BMP without its file header plus an AND mask, or a complete PNG.

ICO is the better choice for favicons and Windows icons, while EXR suits visual effects, compositing and 3D render output.

ICO strengths: Multiple sizes in one file; Required by Windows and supported by every browser as a favicon. Drawbacks to weigh: Max 256×256 per image; Not for photos.