The file extension IRS marks preference files for the 'Save to Web' feature of Photoshop's image-editing software and Illustrator's vector-drawing software Adobe. In an IRS file the image format, for example JPEG or PNG-8, the quality settings as well as size and further optimization settings are stored.
You can reach the function via 'File -> save for web'. If you click on the default arrow and select 'Change output settings' you can load and save IRS files. In this way, you can easily apply a fixed optimization to all images on a web page.
Under 'Preferences / Optimized Settings' you will find various pre-installed settings files. A less commonly used extension for these settings files is iros.
Most often resolving problems with opening IRS files is very simple. Just install an appropriate program that supports such files. All of the listed programs support IRS files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of IRS files or offer file conversion options, but may not be capable of editing such files.
It is possible that although a compatible program has been installed on user’s system, it is not used by the system to open it. This may happen because no default application was associated with this type of files. To associate IRS files with given application, select "Open with" from drop-down menu (accessed by right-clicking on the file). Then select from the list the program or application you want to be used to open this type of file. If the Adobe Photoshop applications is not on the list, select "Browse" option in order to manually locate the directory where Adobe Photoshop has been installed.
Sometimes problems with opening IRS files may not lie with the application itself, but can arise due to other causes, such as: