Raster Image Formats Guide

Raster images are the most common type of digital image. Composed of pixels arranged in a grid, raster formats are ideal for photographs, digital art, and complex imagery with color gradients and fine details.

This guide explains how raster images work, compares popular formats, and helps you choose the right one for your needs.

What Are Raster Images?

Raster images (also called bitmap images) store visual information as a grid of individual pixels. Each pixel contains color data, and together they form the complete image.

Key characteristics:

• Resolution-dependent — Quality is tied to pixel dimensions
• Fixed size — Scaling up causes quality loss (pixelation)
• Rich detail — Can represent complex colors and gradients
• Larger files — More pixels = larger file size

Raster vs. Vector

Characteristic	Raster Images	Vector Images
Composition	Pixels (grid)	Mathematical paths
Scaling	Quality degrades	Infinite scalability
Best for	Photos, complex imagery	Logos, illustrations
File size	Larger for high resolution	Smaller, resolution-independent
Editing	Pixel-level manipulation	Shape and path manipulation
Common formats	JPEG, PNG, GIF, TIFF	SVG, AI, EPS

Common Raster Formats

JPEG (Joint Photographic Experts Group)

The most widely used format for photographs and web images.

Characteristics:

• Lossy compression (reduces file size by discarding data)
• 24-bit color (16.7 million colors)
• No transparency support
• Variable compression levels

Best for:

• Photographs
• Web images where file size matters
• Images with complex color gradients
• Social media and email sharing

Limitations:

• Quality degrades with each save
• No transparency
• Compression artifacts on sharp edges

Typical use cases:

Use	Quality Setting	File Size
Web display	70-80%	Small
Email sharing	60-70%	Very small
High quality	90-95%	Medium
Print	100%	Large

PNG (Portable Network Graphics)

The standard for lossless web graphics with transparency support.

Characteristics:

• Lossless compression (no quality loss)
• Full alpha channel transparency
• 8-bit (256 colors) or 24-bit (16.7 million colors)
• Larger files than JPEG for photographs

Best for:

• Graphics with transparency
• Screenshots and UI elements
• Logos and icons on websites
• Images with text or sharp edges
• Images requiring multiple edits

Limitations:

• Larger file sizes for photographs
• No animation (use APNG or WebP instead)

GIF (Graphics Interchange Format)

Simple format supporting animation and basic transparency. Despite its age, GIF remains relevant for specific use cases — our GIF format guide covers when it still makes sense and when you should convert to something better.

Characteristics:

• Lossless compression (LZW)
• Limited to 256 colors (8-bit)
• Binary transparency (on/off, no partial transparency)
• Animation support

Best for:

• Simple animations
• Graphics with few colors
• Small icons and buttons
• Memes and reaction images

Limitations:

• 256 color limit causes banding in photographs
• Not suitable for photos
• Largely superseded by WebP for web use

TIFF (Tagged Image File Format)

Professional format for high-quality and archival purposes.

Characteristics:

• Supports lossless and lossy compression
• High bit depth (up to 32-bit per channel)
• Multiple pages and layers
• Extensive metadata support
• CMYK color space for printing

Best for:

• Professional printing
• Image archival
• Scanned documents
• Photography masters
• Medical and scientific imaging

Limitations:

• Very large file sizes
• Not supported by web browsers
• Overkill for everyday use

WebP

Modern format combining JPEG and PNG benefits.

Characteristics:

• Supports both lossy and lossless compression
• Full transparency support
• Animation support
• 25-35% smaller than JPEG at equivalent quality
• Supported by all modern browsers

Best for:

• Web images (photos and graphics)
• When both quality and file size matter
• Modern web projects

Limitations:

• Not supported by some older software
• Less universal than JPEG/PNG outside web

BMP (Bitmap)

Simple, uncompressed format for Windows. If you’re stuck with BMP files from legacy systems, our BMP conversion guide walks through the best migration paths to modern formats.

Characteristics:

• Usually uncompressed
• Large file sizes
• Simple structure

Best for:

• Legacy Windows applications
• When no compression is acceptable

Limitations:

• Extremely large files
• Not practical for web or sharing

Format Comparison

Format	Compression	Transparency	Animation	Color Depth	Best For
JPEG	Lossy	No	No	24-bit	Photos
PNG	Lossless	Yes (alpha)	No	8/24/32-bit	Graphics, screenshots
GIF	Lossless	Yes (binary)	Yes	8-bit	Simple animations
TIFF	Both	Yes	No	Up to 32-bit	Print, archival
WebP	Both	Yes	Yes	24-bit	Web (modern)
BMP	None	No	No	Up to 32-bit	Legacy Windows

Choosing the Right Format

For Web Use

Photographs: JPEG (or WebP for modern browsers)

• Use 70-85% quality for good balance

Graphics with transparency: PNG (or WebP)

• Use PNG-8 for simple graphics with few colors
• Use PNG-24/32 for complex graphics or photography with transparency

Animations: WebP (or GIF for maximum compatibility)

For Print

TIFF for:

• Professional printing
• When printer requires it
• Maximum quality preservation

High-quality JPEG acceptable for:

• Photo printing services
• When TIFF isn’t required

For Archival

TIFF for:

• Long-term storage
• Photography archives
• Important documents

PNG for:

• Simpler graphics
• Web-originated content

Working with Raster Images

Resolution Considerations

Raster image quality depends on resolution:

For web (screen display):

• 72-96 PPI is standard
• Pixel dimensions matter more than PPI setting
• Common widths: 800-2000px depending on use

For print:

• 300 DPI minimum at print size
• Higher resolution = larger file

Calculating print size:

• Print width (inches) = Pixel width ÷ DPI
• Example: 3000px ÷ 300 DPI = 10 inches

Compression and Quality

Lossy compression (JPEG):

• 90-100%: Minimal loss, large files
• 80-90%: Good quality, moderate savings
• 70-80%: Acceptable for web, good compression
• Below 70%: Noticeable artifacts

Lossless compression (PNG):

• No quality loss
• Compression level affects encoding time, not quality
• File size varies by image content

Common Mistakes to Avoid

Saving JPEG multiple times:

• Each save degrades quality
• Edit in lossless format, export to JPEG once

Using PNG for photographs:

• Results in unnecessarily large files
• JPEG provides better compression for photos

Using JPEG for graphics with text:

• Compression causes artifacts around sharp edges
• Use PNG for text and line art

Scaling up raster images:

• Can’t add detail that doesn’t exist
• Results in blurry, pixelated images

Batch Processing Raster Images

For efficient handling of multiple images, use batch processing tools.

BulkImagePro handles common raster operations:

• Resize images — Change dimensions while maintaining quality
• Compress files — Reduce file sizes for web
• Convert formats — Switch between JPEG, PNG, and WebP (see our format conversion guide for detailed best practices)
• Crop to ratios — Standardize aspect ratios

FAQ

When should I use JPEG vs. PNG?

Use JPEG for photographs where file size matters and transparency isn’t needed. Use PNG for graphics with transparency, text, or sharp edges.

Why do my JPEGs look worse each time I save them?

JPEG uses lossy compression. Each save discards more data. Keep master files in lossless formats (TIFF, PNG, PSD) and export to JPEG only for final delivery.

What’s the best format for web images?

WebP offers the best compression with quality for modern browsers. JPEG works universally for photos. PNG for graphics needing transparency.

How do I know if my image has enough resolution for printing?

Divide pixel dimensions by 300. A 3000×2000 pixel image prints at 10×6.7 inches at 300 DPI. Check with your printer for their specific requirements.

Can I convert a raster image to vector?

Auto-tracing tools can approximate vectors from raster images, but results depend on image complexity. Simple graphics convert better than photographs. True vector conversion requires manual redrawing.

Why is my PNG so much larger than my JPEG?

PNG uses lossless compression, preserving all data. JPEG’s lossy compression discards data to achieve smaller files. For photographs, JPEG is typically 5-10x smaller.

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