NVGIF (Not Very Good Image Format) is a compact, versioned image format designed for simplicity, modularity, and offline experimentation. What started as a joke name became a flexible spec with alpha support, per-row compression, and decoders in both Python and C#—which, by all reasonable metrics, makes it a standard.
NVGIF doesn’t aim to be a universal format. It aims to be yours. And it shall always remain Not Very Good, proudly and permanently.
All NVGIF files declare their version in a fixed position within the header:
| Offset | Field | Description |
|---|---|---|
| 0–2 | Magic | Always "NVG" |
| 3 | Version | Format version (1–4) |
| 4+ | Payload | Version-specific header/data |
Because the version byte is always at offset 3, older decoders can reliably detect when they encounter a newer file. For example, a v1-only decoder will correctly identify a v2 or v4 file as unsupported—instead of misreading or crashing—since it can inspect the version byte early and bail out gracefully.
🔒 This makes NVGIF intentionally incompatible but safely recognizable across versions—ensuring forwards- and backwards-facing tools fail predictably, not silently.
AirSquirrel is a lightweight web browser built using WebView2 for smooth, offline-friendly browsing. While primarily a general-purpose browser, it includes native support for .nvg images: AirSquirrel intercepts requests for NVGIF files and converts them to standard PNGs at runtime, allowing seamless viewing directly in the browser.
It features custom alerts, favicon overrides, PDF export, and a customizable Speed Dial interface (served from disk).
AirSquirrel also serves as the C# reference implementation of the NVGIF decoder discussed earlier in this document.
A standalone NVGIF encoder/decoder is available as a command-line utility for Windows. It supports version-aware encoding, decoding, and header inspection across all NVGIF versions.
You can download the latest NVGIF CLI here.
⚠️ Google Drive may warn that it can't scan this file for viruses. This is expected for
.exefiles and doesn't indicate a problem—it's simply too large for Drive’s built-in scanner. The file is safe and was built from source using the Python implementation of the NVGIF spec.
This tool is ideal for scripting, testing, or integrating NVGIF into your own pipelines—no GUI required.
Encode a PNG file into NVGIF v4:
nvgif.exe encode input.png output.nvg --version 4
Convert an .nvg file back into a standard PNG:
nvgif.exe decode input.nvg output.png
Display an NVGIF file's header and metadata:
nvgif.exe info input.nvg
Update an .nvg file to a newer NVGIF version:
nvgif.exe update old.nvg updated.nvg --version 4
Re-encodes
old.nvgas NVGIF v4 using default compression (e.g.rlezlibif unspecified).
Customize compression and alpha support:
nvgif.exe update input.nvg output.nvg --version 4 --compression rle --alpha
Converts to v4 using RLE compression and enables transparency.
Downgrade to v2 for compatibility testing:
nvgif.exe update image.nvg legacy.nvg --version 2 --compression rle
Produces a v2-compatible file with RLE compression, suitable for older decoders.
Let NVGIF CLI choose sensible defaults:
nvgif.exe update input.nvg output.nvg
Uses default target version (v4) and matching default compression settings.
View an NVGIF image in a resizable window:
nvgif.exe view image.nvg
Launches a graphical window with the image rendered over a checkerboard background (for transparency), auto-scaled to fit the screen. Handy for previewing
.nvgfiles without converting to PNG.
For more options, run:
nvgif.exe --help
These examples assume you're running the CLI in the same directory as the executable. Adjust paths as needed!