Dear Milad Sakkaki

If the use of "COMSOL", you can increase resolution when saving images.

In the "photoshop" when creating a new project, you can increase resolution.

Kourosh Vaferi

Thanks a lot for your help. But what about images that do not have DPI setting?

Dear Milad

Use the image size option and increase the resolution

Dear Milad Sakkaki ,

Go to Image > Adjustments > Levels

Then you can increase the quality of image by changing the Input and Output levels.

https://www.howtogeek.com/105952/3-simple-ways-to-improve-low-resolution-images-and-typography/

https://www.wikihow.com/Improve-Digital-Photo-Quality-in-Photoshop