Users that have less knowledge on using Adobe Photoshop sometimes ask “Why I can’t save this image into a .PNG format. Well there are 2 the solutions.
1. (For this method only: Ctrl+Shift+S or Ctrl+S) You cannot save your image into a .PNG format because the Image Color mode of the document is set to CMYK and there is no solution for that to save an image into .PNG format while in CMYK color mode.
All you can do is change the color mode to RGB by going to the Menu>Image>Mode>RGB color.
2. The 2nd method is you don’t have to convert the color mode of your document to RGB. All you have to do is press Ctrl+Shift+Alt+S and then a pop-up dialog and choose PNG-8 or PNG-24 in able for you to save your image in .PNG format.