Image Optimisation Guide
Everything you need to know about image formats, quality settings, dimensions, and compression to get the best results from ImgTools.
In This Guide
1. When to Use Each Format
Choosing the right image format is the single most impactful decision for file size and quality. Each format has strengths that make it ideal for specific use cases.
JPEG is the standard for photographs and images with complex colour gradients. It uses lossy compression, meaning some quality is sacrificed for smaller file sizes. At quality levels above 75%, the loss is barely perceptible to the human eye. JPEG does not support transparency.
Best for: Photos, product images, backgrounds, hero images, portrait photography.
PNG uses lossless compression, preserving every pixel perfectly. This makes it ideal for screenshots, logos, icons, and any image that requires transparency (alpha channel). The trade-off is larger file sizes compared to JPEG or WebP for photographic content.
Best for: Screenshots, logos, icons, diagrams, text overlays, images needing transparency.
WebP is Google's modern image format that provides superior compression for both lossy and lossless images. It typically achieves 25-35% smaller file sizes than JPEG at equivalent quality, and supports transparency like PNG. All modern browsers support WebP, making it the best choice for web performance.
Best for: Website images, blog posts, e-commerce, any web content where file size matters.
2. Recommended Quality Settings
Quality settings control the trade-off between file size and visual fidelity. These recommendations apply to JPEG and WebP formats. PNG is always lossless, so quality settings do not apply.
| Use Case | Quality Range | Notes |
|---|---|---|
| Web pages & blogs | 75 – 85% | Best balance of quality and load speed. Ideal for most website images. |
| Social media | 80 – 90% | Slightly higher quality as platforms apply their own re-compression. |
| E-commerce products | 85 – 92% | Higher quality to show product details clearly. Zoom-friendly. |
| Email newsletters | 70 – 80% | Lower quality acceptable. Keep total email size under 1 MB. |
| Print / archival | 100% | Maximum quality. File size is less important for print. |
3. Image Dimensions for Social Media
Each social media platform has recommended image dimensions. Using the correct size avoids cropping and ensures your images look sharp. Use the Resize tool to match these dimensions exactly.
Twitter / X
4. Understanding Compression
Image compression reduces file size by removing data. There are two fundamental approaches, and understanding the difference helps you make better choices.
Lossy Compression
Permanently removes some image data to achieve smaller file sizes. The removed data cannot be recovered. At moderate quality levels (75-90%), the visual difference is usually imperceptible.
Formats: JPEG, WebP (lossy mode)
Typical savings: 60-95% smaller than uncompressed
Use when: File size matters more than pixel-perfect quality
Lossless Compression
Reduces file size without any quality loss. The decompressed image is identical to the original, pixel for pixel. File sizes are larger than lossy compression but quality is preserved perfectly.
Formats: PNG, WebP (lossless mode)
Typical savings: 20-60% smaller than uncompressed
Use when: Quality must be preserved exactly (logos, screenshots)
Re-compression Warning
Each time you compress a lossy image (JPEG or lossy WebP), quality degrades slightly. Avoid compressing the same image multiple times. Always start from the original, highest-quality version when possible. This is sometimes called "generation loss."
5. Batch Processing Tips
ImgTools's Compress, Convert, and Bulk Resize tools support processing multiple images at once. Here are some tips for efficient batch processing.
- 1
Group similar images together
Process photos separately from screenshots. They often need different formats and quality settings.
- 2
Process in batches of 10-15 files
Very large batches can consume significant browser memory. Smaller batches are more reliable.
- 3
Use "Max Width" mode for web images
In the Bulk Resize tool, "Max Width" mode scales down images wider than your target while leaving smaller images untouched. Set it to 1200px or 1920px for most web use cases.
- 4
Convert to WebP for maximum savings
If your website supports WebP (most modern sites do), converting from JPEG or PNG to WebP can reduce file sizes by 25-35% with no visible quality loss.
- 5
Test with a single image first
Before processing a large batch, test your settings on one image to make sure the output quality and dimensions meet your requirements.
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