On the Samsung Galaxy S7 you have the option to start the camera quickly with the home button. So you can open the camera quickly by rapid double pressing the home button.
If the function on your Samsung Galaxy S7 is not be enabled, please proceed as follows:
Open from the start screen the camera app and from there the settings. Scroll down to "Quick Start" and then tap on the entry to activate that function.
You can then open the camera at any time very quickly by pressing twice in quick succession on the home button.