Generated file types
Picfairy offers different results for each file, including the most advanced compressions algorithm such as Webp or quantized PNG.
Because Picfairy displays all possible versions of the original images in an convenient readable layout, you can easily evaluate which versions you want to retain according to the desired weight.
Jpeg
Jpeg is on of the oldest compression algorithm available and probably the most used across the web also.
It is widely supported and offer a good compression ratio for the Bitmap image type it tried to enhance back in time.
Webp
Webp is an algorithm that offers files 25% smaller than JPEG at same perceived quality. When compression ratio is increased (and then image quality is decreased) Webp tends to show less artifacts than Jpeg but it also smoothen off more details in low contrast areas than Jpeg.
It is currently supported by 95% of browsers but it is safe to offer an alternate image such as Jpeg (please see bottom of page for details on how to offer alternate image).
PNG 8 bits
PNG is a lossless file format and therefore shows no artifact.
Though, in order to make it a good candidate for compression, we haved decrease the number of colors to 256 (8bits).
Why? Because this limitation is not always a problem for some type of images, and because the human eye may not see a difference between gradients of colors very close to each other.
We offer PNG 8bits when unique colors of original image are inferior to 15.000 and total pixels inferior to 300.000. And if a downsize is requested ... we tweak a bit these numbers.
AVIF
Avif is a brand new compression algorithm that offers even better compression than Webp.
Yet only 70% of browsers support it at the moment. These images need to be added through an HTML <picture> tag in order to offer an alternative image at all time.
Unfortunately AVIF is really slow to read and to convert to. Picfairy conversion to AVIF has been removed for the moment as it is too CPU intensive. We are still watching any improvements on the compression algorithm but we suspect it might also be a problem on the client side: if a browser supports AVIF it may still display the image with a delay. Which may make compression useless.
Smaller devices like entry level smartphones may struggle further...
You may visit Google's Squoosh app for advanced compression if you really need AVIF