Implement convert functions for RGB(A)

src/Tools/tool_helper/src/lib.rs

@@ -22,6 +22,10 @@ impl Error {
         Error::from_text(error.to_string())
     }
 
+    pub fn from_callback<F>(callback: F) -> Error where F: Fn() -> String {
+        Error::from_text(callback())
+    }
+
     pub fn not_implemented(function: &str) -> Error {
         Error::from_text(format!("{} not implemented yet", function))
     }
@@ -38,7 +42,7 @@ impl Error {
     }
 
     pub fn ok_or_new<T, F>(option: Option<T>, error_text: F) -> Result<T, Error> where F: Fn () -> String{
-        Ok(option.ok_or(Error{exit_code: Self::DEFAULT_EXITCODE, action: String::new(), text: error_text()})?)
+        Ok(option.ok_or(Error::from_callback(error_text))?)
     }
 }