Image Quality Explained

Image quality is one of the most critical parameters in modern digital imaging, especially when working with compressed formats such as JPEG, WEBP, and HEIC. This setting directly controls the balance between visual clarity and file size, making it a decisive factor for website performance, storage efficiency, and overall user experience.

This parameter only applies to JPEG, WEBP, and HEIC images. For other image formats, such as PNG, BMP, or TIFF, the image quality setting is ignored because these formats use different compression methods or are entirely lossless by design.

Understanding how image quality works—and how to choose the right level—can help you achieve faster loading times, reduced bandwidth usage, and visually appealing images without unnecessary file size inflation.

What Is Image Quality?

Image quality refers to the degree of compression applied to an image during encoding. It determines how much image data is preserved and how much is discarded to reduce file size.

• Higher image quality preserves more visual details but produces larger file sizes.
• Lower image quality removes more data, resulting in smaller files but potentially visible artifacts.

This process is known as lossy compression, where some original information is permanently removed to optimize storage and performance.

Supported Formats and Why Quality Matters

The image quality parameter is applicable only to the following formats:

JPEG (Joint Photographic Experts Group)

• Most widely used image format on the web
• Uses lossy compression
• Allows fine-grained control over image quality
• Ideal for photographs
• Excellent balance between size and quality
• Highly sensitive to quality adjustments

WEBP

• Modern image format developed by Google
• Supports both lossy and lossless compression
• Smaller file sizes than JPEG at similar quality
• Better compression efficiency
• Widely supported by modern browsers

HEIC (High Efficiency Image Container)

• Commonly used by Apple devices
• Based on HEVC compression
• Superior compression efficiency
• High image quality at very small file sizes
• Increasing support across platforms

For PNG, BMP, SVG, or TIFF, the image quality parameter does not apply and will be ignored.

How Image Quality Affects File Size

The relationship between image quality and file size is direct and proportional.

High Quality = Larger File Size

• Minimal compression is applied
• Fine textures and color gradients are preserved
• File size increases significantly

Low Quality = Smaller File Size

• More data is removed
• Compression artifacts may appear
• File size becomes dramatically smaller

Examples:

• A JPEG image at 90% quality may be 3–5× larger than the same image at 60% quality
• Reducing quality from 100% to 85% often cuts file size by nearly half with minimal visible difference

Visual Differences Across Quality Levels

100% Quality

• Near-lossless appearance
• Very large file size
• Often unnecessary for web usage

80–90% Quality (Recommended)

• Excellent visual fidelity
• Minimal artifacts
• Optimal balance for websites and apps

60–70% Quality

• Slight softening of details
• Minor compression artifacts
• Significant file size reduction

Below 50% Quality

• Noticeable pixelation
• Color banding and blur
• Best suited for thumbnails or previews

Compression Artifacts Explained

• Blockiness: Visible square blocks in detailed areas
• Blurring: Loss of sharp edges and textures
• Color Banding: Smooth gradients break into visible steps
• Noise Amplification: Compression exaggerates image noise

Modern formats like WEBP and HEIC minimize these effects better than JPEG, especially at lower quality settings.

Why Image Quality Is Ignored for Some Formats

PNG

• Uses lossless compression
• Preserves every pixel exactly
• Quality slider has no effect

BMP

• Uncompressed format
• Very large file sizes
• No compression control

SVG

• Vector-based format
• Resolution-independent
• Quality does not apply

Choosing the Right Image Quality

• Websites & Blogs: 70–85%
• E-commerce Images: 80–90%
• Social Media: 70–80%
• Thumbnails: 40–60%
• Print & Archive: 90–100%

Performance and SEO Impact

Optimized image quality improves page load speed, Core Web Vitals, bounce rate, and search engine rankings. Smaller files result in faster rendering, reduced bandwidth usage, and better mobile performance.

Image Quality vs Image Resolution

• Resolution controls image dimensions
• Quality controls compression level
• Best results come from combining both

Best Practices

• Never use 100% quality unless necessary
• Test multiple quality levels visually
• Prefer WEBP or HEIC when supported
• Combine quality reduction with resizing
• Use consistent quality across your site
• Preview images before publishing

Why This Parameter Is Essential

The image quality setting gives users full control over file size, flexible optimization options, compatibility with modern formats, and professional-grade output customization. Any serious image compression or conversion tool must include this parameter.