How to Compress Images Without Losing Quality (Complete 2025 Guide)

What is image compression?

Image compression is the process of reducing the file size of an image by removing redundant or unnecessary data. The goal is to achieve the smallest possible file while maintaining acceptable visual quality for the intended use.

When a camera takes a photo, it stores an enormous amount of information: the exact color of each of the millions of pixels. Much of that data is redundant — areas of solid blue sky, for example, don't need to describe each pixel individually. Compression algorithms exploit these redundancies to reduce file size.

Lossy vs lossless compression

There are two fundamental types of compression:

Lossless compression

The compressed file contains exactly the same information as the original. When decompressed, you recover every pixel identical to the original. PNG and lossless WebP use this method.

• Advantage: Perfect quality, ideal for logos, screenshots and graphics with text.
• Disadvantage: Size reduction is more limited (20–60%).

Lossy compression

The algorithm discards information that the human eye can barely perceive — fine details in high-contrast areas, subtle color variations. The result is a much smaller file that looks virtually identical.

• Advantage: Size reductions of 60–90% while maintaining excellent visual quality.
• Disadvantage: Small, irreversible information loss. Never re-compress a JPEG from another already-compressed JPEG.

What quality setting should you choose?

Most compression tools use a scale from 1 to 100, where 100 is maximum quality and 1 is maximum compression. Here are recommendations by use case:

Use case	Recommended quality	Typical reduction
Product photography (e-commerce)	85–90%	50–70%
Blog and article images	75–85%	60–80%
Thumbnails and secondary images	65–75%	70–85%
Large backgrounds and banners	60–70%	75–90%
WhatsApp / social media images	70–80%	65–80%

80% is the sweet spot for most web images — excellent visual quality with 60–75% file size reductions.

Format comparison: JPG, PNG, WebP, AVIF

Format	Type	Relative size	Transparency	Compatibility
JPEG/JPG	Lossy	100% (baseline)	No	Universal
PNG	Lossless	120–200%	Yes	Universal
WebP	Both	65–75%	Yes	95%+ browsers
AVIF	Both	50–60%	Yes	80% browsers

When to use each format

Use JPG when:

• The image is a photograph with many colors and gradients.
• You don't need transparency.
• Universal compatibility is critical (emails, legacy systems).

Use PNG when:

• You need transparency (logos, icons, screenshots with transparent backgrounds).
• The image has text, sharp lines or flat colors (graphics, diagrams).
• Perfect quality is prioritized over file size.

Use WebP when:

• Your website needs maximum performance.
• You want the best balance of quality, size and compatibility.
• It is the best option for most web images in 2025.

How to compress images step by step

The fastest and most private method is to use an online tool that processes images directly in your browser, without uploading your files to any server.

1. Open ComprimirPro: Go to comprimirpro.com/en from any device.
2. Upload your image: Drag one or more JPG, PNG or WebP files into the upload area, or click to select them.
3. Adjust quality: Move the slider to the desired value. For most web images, 80% is the ideal point.
4. Choose output format: For maximum savings, select WebP. For universal compatibility, keep the original format.
5. Compress and download: Click "Compress all" and download your optimized images.

Common mistakes when compressing images

1. Re-compressing an already compressed JPEG

Every time you save a JPEG from an already-compressed JPEG, the algorithm applies additional losses. After 3–4 cycles, the degradation becomes visible. Solution: always work from the original file (RAW, TIFF or high-quality PNG).

2. Using PNG for photographs

PNG is lossless, so a photograph in PNG format will weigh 3–5 times more than the same image in JPEG or WebP with no appreciable visual difference. Reserve PNG for logos, graphics and images requiring transparency.

3. Not resizing before compressing

A 4000×3000px image published on a blog where it displays at 800×600px carries four times more data than needed. Resize first to the actual display dimensions, then compress.

4. Ignoring metadata

Camera photos include EXIF metadata (GPS location, camera model, date) that can add 50–200 KB per image. Stripping this during compression can provide significant additional savings.

SEO and Core Web Vitals impact

Optimized images have a direct, measurable impact on your website's SEO through Google's Core Web Vitals:

LCP (Largest Contentful Paint)

LCP measures how long it takes for the largest visual element to load — often a hero or product image. Google considers LCP "good" when it's under 2.5 seconds. A 2 MB image can push LCP to 4–6 seconds on mobile connections. The same image compressed to 200 KB can bring it down to 1.5 seconds.

CLS (Cumulative Layout Shift)

Images without defined dimensions cause layout jumps while loading, penalizing CLS. While not directly a compression issue, lighter images load faster, reducing the window of time during which these shifts occur.

Google Image indexing

Google can crawl and index your images in Google Images, generating additional traffic. Lighter images are indexed faster. Combine weight optimization with a good descriptive alt attribute to maximize ranking potential.

In summary: compressing images is not just a technical best practice — it's one of the most effective actions you can take to improve user experience, SEO and conversion rates on your website. Start today with our free tool.