Lossy or lossless: which compression should I use for web images?

Use lossy (JPG, WebP, AVIF) for photographs — the human eye barely notices the difference at quality 80–85, and file sizes are 5–20× smaller. Use lossless (PNG, WebP-lossless) for screenshots, UI mockups, logos and anything with sharp edges or text — lossy creates ugly artifacts around boundaries.

Does conversion preserve EXIF metadata (camera, GPS, date)?

It depends on the tool: ImageMagick and FFmpeg copy EXIF by default, while cwebp drops it unless you pass -metadata all . KaijuConverter strips metadata server-side after conversion to protect your privacy — if you need to keep camera or GPS data, use a desktop tool you control.

Lossy or lossless: which compression should I use for web images?

Use lossy (JPG, WebP, AVIF) for photographs — the human eye barely notices the difference at quality 80–85, and file sizes are 5–20× smaller. Use lossless (PNG, WebP-lossless) for screenshots, UI mockups, logos and anything with sharp edges or text — lossy creates ugly artifacts around boundaries.

Does conversion preserve EXIF metadata (camera, GPS, date)?

It depends on the tool: ImageMagick and FFmpeg copy EXIF by default, while cwebp drops it unless you pass -metadata all . KaijuConverter strips metadata server-side after conversion to protect your privacy — if you need to keep camera or GPS data, use a desktop tool you control.

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GIF Format: Complete Technical Guide to Animation, Interlacing, Color Palette & Transparency

Guide

GIF Format: Complete Technical Guide to Animation, Interlacing, Color Palette & Transparency

PC By Pablo Cirre • Updated May 7, 2026

GIF: Graphics Interchange Format for Animation & Graphics

GIF (Graphics Interchange Format) was introduced in 1987 as a platform-independent image format. While GIF has been superseded by PNG (lossless graphics), WebP (animation), and modern video, GIF remains ubiquitous for simple animations, memes, and web compatibility. Understanding GIF structure is essential for legacy web content and optimizing animated graphics.

GIF File Structure: Header & Logical Screen Descriptor

Every GIF file follows a strict binary structure:

G I F 8 9 a                (signature — 'GIF89a' for animated, 'GIF87a' for static)
[Logical Screen Descriptor — 7 bytes]
[Global Color Table — optional, up to 768 bytes]
[Data stream — images, text, extensions]
;                          (trailer — marks end)

Logical Screen Descriptor (7 bytes):

Byte 0-1:  Canvas Width (16-bit little-endian)
Byte 2-3:  Canvas Height (16-bit little-endian)
Byte 4:    Packed Fields
           Bit 7: Global Color Table Flag (1 = present)
           Bits 6-4: Color Resolution (bits per pixel - 1)
           Bit 3: Sort Flag (1 = sorted by luminance)
           Bits 2-0: Global Color Table Size (2^(N+1) colors)
Byte 5:    Background Color Index (into global palette)
Byte 6:    Pixel Aspect Ratio (0 = square pixels)

Example (256×256 GIF with 256-color palette, no sorting):

Width:       00 01     (256 pixels, little-endian)
Height:      00 01     (256 pixels)
Packed:      F7        (11110111 binary)
             bit 7=1   (global color table present)
             bits 6-4=111 (8 bits per pixel = 256 colors)
             bit 3=0   (not sorted)
             bits 2-0=111 (size = 2^(7+1) = 256)
Background:  00        (color 0)
Aspect:      00        (1:1 ratio)

Color Palette: Global & Local Tables

GIF uses indexed color—every pixel is an index (0–255) into a color table:

Global Color Table (GCT):

256 entries × 3 bytes (RGB) = 768 bytes maximum
Entry 0:   [R0 G0 B0]
Entry 1:   [R1 G1 B1]
…
Entry 255: [R255 G255 B255]

Local Color Table (LCT, per image):

[Image Descriptor]
[Local Color Table — optional, overrides global]
[Image Data]

Used when an image needs a different palette than global (e.g., first frame uses warm colors, second uses cool colors).

Transparency:

[Graphic Control Extension]
Byte 0: Transparency Flag (1 = transparent color specified)
Byte 1: Transparent Color Index (e.g., 255 = magenta is transparent)

Pixels with index matching transparent color index are rendered as transparent (only 1-bit transparency—fully opaque or fully transparent, no alpha blending).

LZW Compression: Dictionary-Based Encoding

GIF uses LZW (Lempel-Ziv-Welch) compression—a lossless algorithm optimized for palette data:

LZW encoding process:

Input: [index sequence from scanlines]
256 initial codes (one per palette entry)
Codes 256+ built dynamically as patterns emerge

Scanline: [0] [1] [0] [1] [0] [1] [2] …
Codes:    [0] [1] [0] [1] [0] [1] [2] [256=01] [257=10] …
Output:   [0] [1] [256] [257] [2]…

Result: frequent patterns (e.g., alternating colors in gradients) are encoded as single codes, achieving ~30–50% compression on graphics.

Animation: Graphic Control Extension & Image Descriptor

Graphic Control Extension (8 bytes):

Byte 0: Extension Introducer (0x21)
Byte 1: Graphic Control Label (0xF9)
Byte 2: Block Size (always 4)
Byte 3: Packed Fields
        Bit 7-5: Reserved
        Bits 4-2: Disposal Method (0=none, 1=leave, 2=restore background, 3=restore previous)
        Bit 1: User Input Flag (1 = animation pauses for user input)
        Bit 0: Transparency Flag (1 = transparent color follows)
Bytes 4-5: Delay Time (10ms units, little-endian)
           e.g., 5 = 50ms (20 FPS)
Byte 6: Transparent Color Index
Byte 7: Block Terminator (0x00)

Image Descriptor (10 bytes):

Byte 0: Image Separator (0x2C)
Bytes 1-2: Image Left Position
Bytes 3-4: Image Top Position
Bytes 5-6: Image Width
Bytes 7-8: Image Height
Byte 9: Packed Fields
        Bit 7: Local Color Table Flag
        Bit 6: Interlace Flag (1 = 4-pass Adam7 interlacing)
        Bit 5: Sort Flag
        Bits 2-0: LCT Size

Animation structure (3-frame GIF):

[GIF Header + Global Color Table]
[Graphic Control Extension — frame 1, delay 50ms]
[Image Descriptor — image 1]
[LZW compressed image data]
[Graphic Control Extension — frame 2, delay 50ms]
[Image Descriptor — image 2]
[LZW compressed image data]
[Graphic Control Extension — frame 3, delay 50ms]
[Image Descriptor — image 3]
[LZW compressed image data]
[Trailer — 0x3B]

Interlacing: 4-Pass Progressive Rendering

GIF supports interlacing for progressive display:

Pass 1: rows 0, 8, 16, 24… (every 8th row)
Pass 2: rows 4, 12, 20, 28… (every 8th, offset 4)
Pass 3: rows 2, 6, 10, 14… (every 4th, offset 2)
Pass 4: rows 1, 3, 5, 7… (every 2nd, odd rows)

Interlaced GIF shows rough preview first, refines progressively. Tradeoff: ~10% larger file (due to additional encoding passes).

GIF vs. Modern Alternatives

Metric	GIF	PNG	WebP	MP4 (H.264)
Animated	✅	❌ (APNG exists)	✅	✅
Palette limitation	256 colors max	Unlimited	Unlimited	Unlimited
Transparency	1-bit (binary)	Full alpha (8-bit)	Full alpha	Full alpha
File size (animation)	2 MB (large)	500 KB (APNG)	400 KB (WebP)	100 KB (MP4 H.264)
Browser support	100%	100%	97%	95%
Patent-free	⚠️ (LZW patent expired 2003)	✅	✅	⚠️ (MPEG LA)

Modern recommendation: Replace GIF with WebP (better compression) or MP4/WebM (video—far superior compression).

Creating & Optimizing GIFs

FFmpeg (MP4 → GIF, 10 FPS):

ffmpeg -i input.mp4 -vf fps=10 -c:v gif output.gif
ffmpeg -i input.mp4 -vf "scale=480:-1,fps=10" output.gif

ImageMagick (image sequence → animated GIF):

convert -delay 10 -loop 0 frame*.png animated.gif
convert -delay 10 animated.gif -resize 50% optimized.gif

Python (Pillow):

from PIL import Image
frames = [Image.open(f) for f in ['frame1.png', 'frame2.png']]
frames[0].save('output.gif', save_all=True, append_images=frames[1:], duration=100, loop=0)

Optimization (gifsicle):

gifsicle -b -O3 --lossy=80 input.gif -o output.gif

GIF remains important for memes and legacy web, but for new projects, WebP animations or video are superior.

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Frequently Asked Questions

GIF (Graphics Interchange Format, 1987) was the only universal lossless animation format for decades. It uses 256-color palette and LZW compression (~50% reduction on graphics). GIF falls to 1-bit transparency (fully opaque/transparent, no alpha blending) and large file sizes compared to modern WebP (40% smaller) or video (10× smaller).

GIF (Graphics Interchange formato, 1987) was the only universal sem perdas animation formato para decades. It uses 256-color palette e LZW compressão (~50% reduction on graphics). GIF falls to 1-bit transparência (fully opaque/transparent, no alpha blending) e large tamanho do arquivos comparado a moderno WebP (40% smaller) ou video (10× smaller).

GIF (Graphics Interchange Format, 1987) was the only universell verlustfrei animation Format für decades. It uses 256-color palette und LZW Komprimierung (~50% reduction on graphics). GIF falls to 1-bit Transparenz (fully opaque/transparent, no alpha blending) und large Dateigrößes im Vergleich zu modern WebP (40% smaller) oder video (10× smaller).

GIF (Graphics Interchange formato, 1987) was the only universal sin pérdidas animation formato para decades. It uses 256-color palette y LZW compresión (~50% reduction on graphics). GIF falls to 1-bit transparencia (fully opaque/transparent, no alpha blending) y large tamaño de archivos comparado con moderno WebP (40% smaller) o video (10× smaller).

Use <strong>lossy</strong> (JPG, WebP, AVIF) for photographs — the human eye barely notices the difference at quality 80–85, and file sizes are 5–20× smaller. Use <strong>lossless</strong> (PNG, WebP-lossless) for screenshots, UI mockups, logos and anything with sharp edges or text — lossy creates ugly artifacts around boundaries.

GIF uses LZW compression—a dictionary-based algorithm that encodes repeated patterns as codes. Limitation: GIF uses indexed color (palette) with max 256 colors, making it unsuitable for photos (millions of colors). PNG supports unlimited colors losslessly; WebP achieves better compression for all content types.

GIF uses LZW compressão—a dictionary-based algorithm that encodes repeated patterns as codes. Limitation: GIF uses indexed color (palette) com max 256 colors, making it unsuitable para photos (millions of colors). PNG suporta unlimited colors sem perdasly; WebP achieves better compressão para all content types.

GIF uses LZW Komprimierung—a dictionary-based algorithm that encodes repeated patterns as codes. Limitation: GIF uses indexed color (palette) mit max 256 colors, making it unsuitable für photos (millions von colors). PNG unterstützt unlimited colors verlustfreily; WebP achieves better Komprimierung für all content types.

GIF uses LZW compresión—a dictionary-based algorithm that encodes repeated patterns as codes. Limitation: GIF uses indexed color (palette) con max 256 colors, making it unsuitable para photos (millions de colors). PNG soporta unlimited colors sin pérdidasly; WebP achieves better compresión para all content types.

For new projects in 2026, WebP is supported by all modern browsers (95%+ of traffic) and saves 25–35% over JPG at the same visual quality. AVIF is even more efficient (40–50% smaller) but encoding is slower and Safari support is recent. Use WebP as the default and AVIF as the progressive enhancement via <code><picture></code> with JPG fallback.

GIF supports 1-bit transparency: one color index is designated as fully transparent, all others fully opaque. PNG supports 8-bit alpha (256 transparency levels per pixel), enabling smooth gradients and anti-aliased edges. For transparency, PNG is superior.

GIF suporta 1-bit transparência: one color index is designated as fully transparente, all others fully opaque. PNG suporta 8-bit alpha (256 transparência levels per pixel), enabling smooth gradients e anti-aliased edges. para transparência, PNG is superior.

GIF unterstützt 1-bit Transparenz: one color index is designated as fully transparent, all others fully opaque. PNG unterstützt 8-bit alpha (256 Transparenz levels per pixel), enabling smooth gradients und anti-aliased edges. für Transparenz, PNG is superior.

GIF soporta 1-bit transparencia: one color index is designated as fully transparente, all others fully opaque. PNG soporta 8-bit alpha (256 transparencia levels per pixel), enabling smooth gradients y anti-aliased edges. para transparencia, PNG is superior.

It depends on the tool: ImageMagick and FFmpeg copy EXIF by default, while cwebp drops it unless you pass <code>-metadata all</code>. KaijuConverter strips metadata server-side after conversion to protect your privacy — if you need to keep camera or GPS data, use a desktop tool you control.

Switch to WebP (40% smaller, better compression) or MP4 H.264 video (10× smaller than GIF for the same animation). GIF is legacy—only use if targeting very old browsers. For new projects, WebP animations or silent MP4 (auto-play, no audio) are the modern standard.

Switch to WebP (40% smaller, better compressão) ou MP4 H.264 video (10× menor que GIF para the same animation). GIF is legacy—only usar if targeting very old browsers. para new projects, WebP animations ou silent MP4 (auto-play, no audio) are the moderno padrão.

Switch to WebP (40% smaller, better Komprimierung) oder MP4 H.264 video (10× kleiner als GIF für the same animation). GIF is legacy—only verwenden if targeting very old browsers. für new projects, WebP animations oder silent MP4 (auto-play, no audio) are the modern Standard.

Switch to WebP (40% smaller, better compresión) o MP4 H.264 video (10× más pequeño que GIF para the same animation). GIF is legacy—only usar if targeting very old browsers. para new projects, WebP animations o silent MP4 (auto-play, no audio) are the moderno estándar.

Three common causes: (1) ICC color profiles dropped during conversion shift colors slightly; (2) chroma subsampling (4:2:0) reduces color accuracy in lossy JPG/WebP; (3) the new format may not support all features of the original (e.g. PNG → JPG drops transparency to white). For pixel-perfect results stick to lossless formats and preserve color profiles explicitly.