Hi there! It sounds like you're having trouble opening Pixomatic on your Samsung SM-T820 tablet. Let's see if we can get this sorted out together.

First, can you let me know if you recently updated your tablet or the Pixomatic app? Also, does the app give you any error messages before it closes? This information will help me guide you more effectively.

In the meantime, here are some basic troubleshooting steps you can try:

1. Restart Your Tablet: Sometimes a simple reboot can resolve app issues. Just turn your tablet off and then back on again.

2. Clear the App Cache: This can help if the app is running into issues launching. Here's how to do that:
- Go to Settings on your tablet.
- Scroll down and tap on Apps or Application Manager.
- Find and tap on Pixomatic.
- Tap on Storage and then select Clear Cache.

3. Check for Updates:
- Open the Google Play Store.
- Search for Pixomatic and see if there is an update available. If so, install it.

4. Uninstall and Reinstall the App:
- From the same Apps menu in Settings, you can choose to uninstall Pixomatic. After uninstalling, go back to the Play Store and reinstall the app.

Please give these steps a try, and let me know how it goes! If the issue persists, we can dive deeper into more advanced solutions.