ICO extension - image format used to store icons in Windows programs, files and folders; contains two bitmaps: 1) AND bitmap - an image mask (which determines which part of the icon is transparent) and 2) XOR bitmap - contains an icon that is superimposed on the image mask, ICO files can be changed to create your own icons. Icons can be of different sizes (16 × 16, 32 × 32, 64 × 64 pixels, etc.) and contain a different number of colors (16 colors, 32, 64, 128, 256, 16-bit, etc.)

The "Favicon.ico" file is used to store a small site logo that appears in the address bar of a web browser. If the site has a favion.ico, then it will appear to the left of the web address when loading any page on the site. The favicon.ico file must be 16x16 pixels and stored in the root directory of the website for the web browser to detect.

The PNG file (Portable Network Graphic) refers to bitmap images. The PNG data contains a specific palette of colors used in the drawing. Such a graphic format is quite often used in the world wide web when assigning different images to web pages. Thanks to the Deflate compression algorithm, bitmaps with the PNG file extension are available for compression without obvious quality loss.

ICO was developed to replace the GIF format, because the latter required paid software for a long time. Among the owners of web resources, PNG images are famous for their excellent characteristics against the background of such formats. PNG supports a color depth of up to 48 bits. The main difference between gifs is that such a graphic file is limited to only 8 bits (256 colors in total). You should know that unlike GIF, PNG does not support animation effects.

You can open a file with the PNG extension using virtually any viewer. In the Windows operating system, you can open PNG by simply double-clicking to view images. PNG documents are also available in any web browser. If the user needs to change the saved image in the PNG version, just use image editing tools such as Adobe Photoshop or Microsoft Windows Photos, as well as Corel PaintShop or ACD Systems.

This file extension is very popular and contains all the necessary graphic information for full-color images of good quality.

Icon files used on MAC computers and other OS X devices use the ICNS extension. This format is used to display a small image (icon) in OS X Finder that represents the corresponding application. ICNS files support images of various sizes. The size varies from 16x16 to 512x512 pixels. Starting with OS x Mountain Lion, ICNS files can support even large images - 1024x1024 pixels. This format supports both single-bit and eight-bit alpha channels, as well as various stages of images, including folder icons in the open and closed state.

An ICNS data usually consists of one or more PNG images. This format is very convenient as a basis for ICNS because it allows for transparency. ICNS format supports the 1-bit format, as well as 8-bit alpha channels. What distinguishes them from Windows ICO is that ICNS document able to contain separate icon resources, i.e. they act more like a container.