SquishPic has two operating modes: free and paid.
In the free mode, you can open, view, and save SID files, and decompress (convert) SID files to another format.
In order to compress (convert) other image files into the SID format, you need a data plan. A data plan allows you to convert a certain amount of data (bytes, megabytes, what have you) from JPEG, PNG, TIFF, or Raw to SID format.
To purchase a data plan, you need an account at Extensis.com.
You can try out SquishPic’s compression for free for 15 days; SID files you create using the trial will have a tasteful watermark applied. To sign up for the trial, click Start Trial in the Welcomescreen.
If you have closed the Welcome screen, do this:
Click Log in.
If you have an Extensis account, enter your email address and password.
If you do not have an account, follow the link in the Log in window to create an account, then return to the window and enter your newly-minted credentials.
After you log in you will be told that you don’t have a data plan (which you already know). Click the link to purchase a plan or sign up for the trial.
(DHJ This process is incomplete)
In order to create SID files (either in trial or paid mode), you need to log in to your Extensis.com account.
Click Log in on the toolbar and enter your Extensis account credentials.
Once you have logged in, the Log in button changes to Hi [Name]; clicking it will show details about your data plan, and allow you to log out.
There is no limit to the number of computers you can log in from at one time; any SID files that are created from those locations will be counted against the data remaining in your plan, so be careful to not post your password to your social media (a good rule of thumb in general).
Act now, and you will also receive this lovely...Photoshop plug-in?
The data plan you use with SquishPic can also be used with our Photoshop plug-in, Compress.
Compress brings the ability to open and save SID files to Photoshop, where you can use all of its tools to do whatever you like to your images.
(Compress allows you to open SID files in Photoshop without using your data plan; from there, you can save the image into any supported Photoshop file at no charge. You only need a data plan with Compress to save to SID format.)
For more information about Compress, see https://www.adobeexchange.com/creativecloud.details.20845.html.
Why would you need both Compress and SquishPic? Well, you might not. But you can use both for free to open SID files (and save them to another format). Using Compress with Photoshop gives you access to lots of other tools, while using SquishPic gives you very fast access to simple operations that might take longer in Photoshop.
SquishPic is a free and fast download on Windows, macOS, and Linux, so you can also recommend it as a viewer and converter for clients and coworkers that you deliver SID images to.