Introducing SmartCompress™ – ShortPixel’s Advanced Image Compression Technology

You can determine an acceptable level of image quality by comparing the structural similarity index of an original image and a compressed image.

In this article you’ll learn how ShortPixel‘s SmartCompress technology uses advanced algorithms to optimize the file size of images without compromising the visual quality, usually surpassing what the human eye can detect.

What is SmartCompress?

“To get ahead of the game, you have to stay ahead of the game.” SmartCompress is a unique approach to image optimization that differs from other services on the market. Rather than simply reducing image quality to a fixed percentage, as many other tools and services do, ShortPixel’s goal is to deliver images that look just as good as the original, but with the smallest possible file size.

To achieve this, ShortPixel uses SmartCompress to compress and optimize images, a technology based on advanced algorithms, including SSIM (structural similarity index). SSIM is a quality assessment method that compares the structural similarity between the original image and the compressed image. It provides a score that ranges from a perfect 1 – representing identical pixel structure – to a 0 – representing low similarity and poor image quality.

Example 1: High compression level = low visual quality

Below you’ll find the original image, while the same image is highly compressed underneath it. The file size has been reduced by 81.31% from 273 KB to 51 KB, but it’s quite obvious that the visual quality has been degraded. The SSIM value of 0.8924 confirms this poor quality..

Example 2: Low compression level = high visual quality

When compressing images by lowering the quality factor to a certain value – a technique used by most image optimization services and plugins – it can be difficult to detect any changes in our test image. However, the file size was reduced by only 10.21% to 245 KB. The SSIM value for this compression level is 0.9907, which is very good, but we can get even better results in terms of file size.

Example 3: SmartCompress = optimal visual quality

Using ShortPixel’s SmartCompress with the Glossy optimization level results in a better compressed version of the picture, indistinguishable from the original to the naked eye, and reduces the file size by 26.73% to 200 KB. The SSIM value of 0.9909 means that the quality of the image is almost identical to the original image, and the file size is smaller compared to the example above.

What is remarkable is that the picture optimized by ShortPixel isn’t only much smaller than the picture compressed with a quality factor 82, but also has a better SSIM factor, which means that it also looks better!

One of the key advantages of SSIM is that it compares images at multiple weighted resolutions and performs scaling in linear-light RGB. This means that it’s sensitive to distortions of different sizes and blends colors correctly to detect errors such as chroma subsampling.

In addition, the algorithm uses the Lab* color space for SSIM calculation, allowing better measurement of brightness and color compared to metrics based on the average of RGB channels. Furthermore, it not only supports alpha channels and images with color profiles, but also uses multi-core CPUs to ensure fast processing.

How does ShortPixel’s SmartCompress technology works to optimize images?

As the images above illustrate, the file size of an image has a direct impact on its quality. To achieve the best results, it is important to find the perfect balance between file size and image quality.

With SmartCompress technology, each image is automatically optimized multiple times with proprietary algorithms until the perfect, smallest possible image is achieved. That means you don’t have to worry about under- or over-optimized images. You can rest assured that your images will look great and load quickly, while keeping file size to a minimum.

Here you can see how ShortPixel’s SmartCompress compares to the optimization methods of other image compression tools and software:

pexels pixabay 417273 original
Original file resized to 1500×1000 – 1.10MB
pexels pixabay 417273 shortpixel
ShortPixel – Glossy compression – 213KB – Reduced by 80.63%
pexels pixabay 417273 imagify
Imagify – 383KB – Reduced by 65.18%
pexels pixabay 417273 tinypng
TinyPNG – 353KB – Reduced by 67.90%
pexels pixabay 417273 resmushit – 327KB – Reduced by 70.27%
pexels pixabay 417273 kraken io – 327KB – Reduced by 70.27%
pexels pixabay 417273 adobe photoshop 65
Adobe Photoshop (Save for web at 65% quality) – 309KB – Reduced by 71.90%

As demonstrated, ShortPixel’s SmartCompress is the clear winner here by significantly reducing the file size by 80.63%, from 1.10MB to 213KB without even using Lossy compression (the most aggressive level), maintaining high quality at a much smaller file size.

? If you know of a service that outperforms ShortPixel in terms of compression ratio (i.e. higher image quality with smaller file size), contact us and we’ll be happy to award you free image optimization credits! 🙂


In summary, ShortPixel’s SmartCompress technology is a game-changer in the image optimization space, by providing a unique method that maintains high image quality while dramatically reducing file size. It fully optimizes images without compromising visual appeal.

If you’re a website owner who wants to improve the performance and visual appeal of your website through advanced image compression and optimization, you can try SmartCompress for free and see the results for yourself.