About

BPG (Better Portable Graphics) delivers superior compression over JPEG and PNG using HEVC intra-frame coding, but browser support remains nonexistent. Converting to GIF ensures universal compatibility at the cost of palette depth - GIF enforces a strict 256-color limit per frame via indexed color tables. This converter implements client-side Median Cut quantization to extract optimal palettes and Floyd-Steinberg dithering to mask banding artifacts. The risk of poor conversion lies in choosing aggressive quantization without dithering, producing visible posterization in gradient-heavy images. For photographic BPG sources, enable maximum dithering; for flat graphics, dithering introduces unnecessary noise.

The GIF89a specification permits multiple frames with independent delays, enabling animation from multi-frame BPG sequences. Each frame carries a Local Color Table (LCT) or references a Global Color Table (GCT), compressed via Lempel-Ziv-Welch (LZW) encoding with variable code widths up to 12 bits. Transparency support exists but affects one palette index only - no alpha gradients. This tool processes files entirely in-browser; no server upload occurs, preserving privacy for sensitive imagery.

Formulas

GIF compression relies on the Lempel-Ziv-Welch algorithm, which builds a dictionary of repeated byte sequences during encoding. The compression ratio depends on image complexity and palette usage.

CR = S_originalS_compressed

where CR is compression ratio, S_original is raw pixel data size, and S_compressed is LZW-encoded stream size.

Color quantization via Median Cut partitions the RGB color cube iteratively. For a palette of k colors:

n_splits = log₂(k)

Each split divides the box with the largest color range along its dominant axis (R, G, or B). Final palette colors are computed as the centroid of pixels within each box.

Floyd-Steinberg dithering distributes quantization error to neighboring pixels using these weights:

e_x+1,y += 716 ⋅ err

e_x-1,y+1 += 316 ⋅ err

e_x,y+1 += 516 ⋅ err

e_x+1,y+1 += 116 ⋅ err

where err = original − quantized for each RGB channel independently.

Reference Data

Format	Max Colors	Compression	Animation	Transparency	Browser Support	Typical Use Case
BPG	16.7M (24-bit)	HEVC Intra	Yes (rare)	Alpha channel	None (plugin required)	Archival, high-quality web
GIF	256 indexed	LZW	Yes (native)	1-bit (single color)	Universal	Animations, simple graphics
PNG	16.7M (24-bit)	DEFLATE	APNG (limited)	Alpha channel	Universal	Lossless graphics
JPEG	16.7M (24-bit)	DCT lossy	No	None	Universal	Photographs
WebP	16.7M (24-bit)	VP8/VP8L	Yes	Alpha channel	Modern browsers	Web optimization
AVIF	16.7M+ (HDR)	AV1 Intra	Yes	Alpha channel	Modern browsers	Next-gen web images
HEIF/HEIC	16.7M+ (HDR)	HEVC	Yes	Alpha channel	Safari only	Apple ecosystem
TIFF	16.7M+ (48-bit)	Various	Multi-page	Alpha channel	None (download)	Print, archival
BMP	16.7M (24-bit)	None (RLE opt.)	No	Limited	Universal	Legacy Windows
ICO	16.7M (32-bit)	PNG/BMP	No	Alpha channel	Universal	Favicons

Frequently Asked Questions

GIF's 256-color palette cannot represent smooth gradients. Enable Floyd-Steinberg dithering to introduce noise patterns that simulate intermediate colors. For extreme gradients, consider PNG or WebP as alternative outputs.

Multi-frame BPG files are processed sequentially. Each frame undergoes independent color quantization unless "Global Palette" mode is selected, which analyzes all frames to build a unified 256-color table - useful for maintaining color consistency across animation frames.

BPG supports full alpha channels with 256 opacity levels. GIF supports only binary transparency (fully opaque or fully transparent). Pixels with alpha < 128 become transparent; others become opaque. The transparency color index is set to the least-used palette entry.

BPG uses HEVC intra-frame coding, requiring computationally intensive block decoding, inverse transforms, and prediction reconstruction. This converter processes everything client-side without native codec acceleration. For files exceeding 4000×4000 pixels, expect delays of 10 - 30 seconds.

Yes. The frame delay parameter (in milliseconds) sets the interval between frames in the output GIF. GIF specification rounds delays to 10ms increments. Values below 20ms may render inconsistently across browsers; 100ms (10 fps) is a safe default for animations.

This converter accepts BPG files up to 50MB. Larger files may exhaust browser memory during decoding. If you encounter crashes, close other tabs and retry, or reduce source image dimensions before conversion.