What's an 'index' in this context?

GIF doesn't store true-color pixels; every pixel is really a small number (an index) that points into a limited color table. This tool reports those index numbers and how often each is used, not the colors themselves directly.

How is this different from GIF Color Extractor?

GIF Color Extractor reports actual RGB hex colors. This tool instead reports the underlying numbered palette slot (0-215, plus a reserved transparency slot) that each pixel would occupy under this site's shared re-encoding palette: two different colors can share one index if they quantize to the same slot.

Does this show the exact index bytes stored in my uploaded file?

Not necessarily. The shared codec this whole category uses fully composites every frame to plain RGBA rather than preserving a source file's original index stream, so this reports 'index under this codec's fixed 216-color palette,' which may differ from whatever index scheme the original file used internally. This is a documented, accepted simplification.

What does index 216 mean?

That's the reserved transparency slot; pixels reported at index 216 were fully transparent (alpha 0) in the decoded frame.

GIF Color Index Extractor - Inspect Palette Slot Usage Online

Overview

Introduction

This tool looks past the visible colors of an animated GIF and reports which numbered palette slot each of its pixels would land in under this site's shared 216-color re-encoding palette.

It's a more technical companion to GIF Color Extractor, useful when you care about the underlying index structure rather than just the colors themselves.

What Is GIF Color Index Extractor?

A client-side analysis tool that decodes every frame of an uploaded GIF and maps each pixel's RGB (and alpha) value onto this category's fixed 216-color-plus-transparency palette index, using the exact same mapping function the shared encoder uses.

It reports usage counts and percentages per index, sorted by how often each is used, rather than modifying the image in any way.

How GIF Color Index Extractor Works

Every frame is decoded into RGBA pixel buffers, and each pixel is passed through the shared codec's colorToGifIndex function, the same quantization step that runs during re-encoding.

Index usage is tallied across every frame combined, then reported sorted by frequency, with each non-transparent index's representative hex color looked up from the shared palette table.

When To Use GIF Color Index Extractor

Use it to understand how many distinct palette slots a GIF would actually use if re-encoded through this site's tools.

It pairs naturally with GIF Color Index Randomizer, since both reason about the same underlying index structure.

Often used alongside GIF Color Extractor, GIF Color Index Randomizer and GIF Quantizer.

Features

Advantages

Shows exactly how the shared quantization palette will be used before you commit to a download from any color-reduction tool.
Reports usage as both raw counts and percentages, making it easy to spot which slots barely matter.
Runs entirely client-side; nothing about your GIF is sent anywhere.

Limitations

This reflects this codec's fixed 216-color cube, not necessarily the original file's actual on-disk index table.
It's a read-only report; use GIF Quantizer or GIF Color Reducer if you actually want to change the image based on what you learn here.

Examples

Inspecting index usage of a simple two-tone GIF

Input

A black-and-white animated icon GIF

Output

Two dominant indexes reported (near-black and near-white slots), each with a high percentage share

A visually simple GIF concentrates almost all its pixels into just a couple of the 216 available slots.

Best Practices & Notes

Best Practices

Run this after GIF Quantizer or GIF Color Reducer to confirm how few distinct slots your reduced GIF actually ends up using.
Treat index 216 (transparency) separately from the numbered color slots when reading the results.
Use GIF Color Extractor instead if you want a human-readable color report rather than a technical index breakdown.

Developer Notes

The index-usage math reuses `colorToGifIndex` and `buildGifGlobalColorTable` directly from the shared gif-codec module rather than re-deriving the quantization cube, guaranteeing this report always matches exactly what `encodeGif` would actually do with the same pixels.

GIF Color Index Extractor Use Cases

Verifying how many of the 216 available palette slots a GIF actually uses before deciding on a reduction target
Debugging why a re-encoded GIF's colors shifted, by inspecting which slots pixels quantized into
Understanding the technical palette structure behind this site's shared GIF encoder

Common Mistakes

Assuming reported indexes match a source file's original internal index table exactly; they reflect this codec's own fixed palette instead.
Confusing an index number with a color; two different colors can share the same index.

Tips

A GIF using very few distinct indexes will compress and re-encode with very little visible palette loss.
Cross-check high-usage indexes here against GIF Color Extractor's hex output to connect a slot number back to a real color.

GIF Color Index Extractor