Image Compression Checklist Before Website Launch

Before launching a website, image compression is a critical step to improve loading speed and user experience. Uncompressed images can cause page lag, increase bounce rates, and even affect search engine rankings. This checklist outlines the key items for image compression, helping you verify each one before launch to ensure every image is lightweight and optimized.

1. Confirm Image Format Appropriateness

Different image formats suit different scenarios. Typically, use JPEG for photos and complex gradients, PNG-8 or SVG for icons, logos, and simple graphics, and consider WebP for animations or transparent backgrounds with smaller file sizes. Avoid uncompressed formats like BMP or TIFF. Checklist:

• Are photos converted to JPEG or WebP?
• Are icons and decorative elements using SVG (Scalable Vector Graphics)?
• Have PNG images been checked for color depth (8-bit vs. 24-bit)?
• Have you considered using WebP format (supported by modern browsers)?

2. Control Original Image Dimensions

Uploaded image dimensions should match the actual display size, rather than relying on HTML or CSS to scale down. For example, if the display area is 800px wide, do not upload a 4000px-wide image. Checklist:

• Does each image's maximum width not exceed the layout container's width?
• Is the image height responsive or fixed to avoid stretching or distortion?
• Are responsive images (srcset attribute) used to provide appropriate sizes for different devices?

3. Choose the Right Compression Tool

Compression tools fall into two categories: lossy and lossless. Lossy compression (e.g., TinyPNG) can significantly reduce file size with minimal visible difference, while lossless compression (e.g., ImageOptim) preserves quality but offers lower compression rates. It's recommended to start with lossy compression at 75%-85% quality, and switch if results are insufficient. Common tools include:

• Online tools: TinyPNG, Compressor.io, Squoosh
• Desktop software: ImageOptim, RIOT, Photoshop's "Save for Web"
• Build tools: imagemin (with Webpack, etc.)

4. Balance Quality and File Size

Over-compression can cause artifacts, color banding, or blurriness, harming brand image. After compression, preview the compressed image alongside the original, focusing on text, edges, and gradients. Generally, set JPEG quality between 70%-85%, WebP quality around 80%, and PNG-8 within 256 colors. Checklist:

• Are critical images (e.g., product main images) individually checked for quality?
• Is the compressed file size within a reasonable range (typically under 200KB, smaller for decorative images)?
• Are there visible compression artifacts?

5. Batch Processing and Naming Conventions

If the website has many images, avoid compressing them one by one manually. Use batch processing features or automation scripts. Additionally, image file names should include descriptive keywords (e.g., "blue-tshirt-front.jpg") rather than "IMG_001.jpg". This helps search engines understand image content. Checklist:

• Is batch compression used (e.g., uploading multiple images to TinyPNG simultaneously)?
• Are image file names standardized (lowercase, hyphen-separated, containing keywords)?
• Have alternative images for different resolutions (e.g., Retina screens) been generated?

6. Verify Loading Speed After Compression

After compression, use tools like Google PageSpeed Insights or GTmetrix in a test environment to check image loading. Pay attention to suggestions such as "avoid uncompressed images" and "use appropriate image formats." Checklist:

• Do images account for an excessively high percentage of total page size?
• Are any images missing lazy loading (deferred loading)?
• Are mobile image dimensions properly adapted?