diff --git a/trimage/tools.py b/trimage/tools.py
index 398df9e..f787c8c 100644
--- a/trimage/tools.py
+++ b/trimage/tools.py
@@ -1,9 +1,46 @@
 #!/usr/bin/env python3
 
+import sys
+import errno
+from subprocess import call, PIPE
 
-def human_readable_size(num, suffix='B'):
-    for unit in ['','K','M','G','T','P','E','Z']:
+
+def check_dependencies():
+    """Check if the required command line apps exist."""
+    exe = ".exe" if (sys.platform == "win32") else ""
+    status = True
+    dependencies = {
+        "jpegoptim": "--version",
+        "optipng": "-v",
+        "advpng": "--version",
+        "pngcrush": "-version"
+    }
+
+    for elt in dependencies:
+        retcode = safe_call(elt + exe + " " + dependencies[elt])
+        if retcode != 0:
+            status = False
+            print("[error] please install {}".format(elt), file=sys.stderr)
+
+    return status
+
+
+def safe_call(command):
+    """Cross-platform command-line check."""
+    while True:
+        try:
+            return call(command, shell=True, stdout=PIPE)
+        except OSError as e:
+            if e.errno == errno.EINTR:
+                continue
+            else:
+                raise
+
+
+def human_readable_size(num, suffix="B"):
+    """Bytes to a readable size format"""
+    for unit in ["", "K", "M", "G", "T", "P", "E", "Z"]:
         if abs(num) < 1024.0:
             return "%3.1f%s%s" % (num, unit, suffix)
         num /= 1024.0
-    return "%.1f%s%s" % (num, 'Y', suffix)
+    return "%.1f%s%s" % (num, "Y", suffix)
\ No newline at end of file
diff --git a/trimage/trimage.py b/trimage/trimage.py
index e17f58c..1f9da2b 100644
--- a/trimage/trimage.py
+++ b/trimage/trimage.py
@@ -2,10 +2,9 @@
 
 import time
 import sys
-import errno
 from os import listdir, path, remove, access, W_OK
 from shutil import copy
-from subprocess import call, PIPE
+
 from optparse import OptionParser
 from multiprocessing import cpu_count
 from queue import Queue
@@ -15,8 +14,8 @@ from PyQt5.QtGui import *
 from PyQt5.QtWidgets import *
 
 from ThreadPool import ThreadPool
-from tools import human_readable_size
 from ui import Ui_trimage
+from tools import *
 
 
 VERSION = "1.0.5"
@@ -41,7 +40,7 @@ class StartQt(QMainWindow):
             self.restoreGeometry(self.settings.value("geometry"))
 
         # check if dependencies are installed
-        if not self.check_dependencies():
+        if not check_dependencies():
             quit()
 
         # add quit shortcut
@@ -240,46 +239,12 @@ class StartQt(QMainWindow):
         # enable recompress button
         self.enable_recompress()
 
-    """
-    Helper functions
-    """
-
     def enable_recompress(self):
         """Enable the recompress button."""
         self.ui.recompress.setEnabled(True)
         if QSystemTrayIcon.isSystemTrayAvailable() and not self.cli:
             self.systemtray.recompress.setEnabled(True)
 
-    def check_dependencies(self):
-        """Check if the required command line apps exist."""
-        exe = ".exe" if (sys.platform == "win32") else ""
-        status = True
-        dependencies = {
-            "jpegoptim": "--version",
-            "optipng": "-v",
-            "advpng": "--version",
-            "pngcrush": "-version"
-        }
-
-        for elt in dependencies:
-            retcode = self.safe_call(elt + exe + " " + dependencies[elt])
-            if retcode != 0:
-                status = False
-                print("[error] please install {}".format(elt), file=sys.stderr)
-
-        return status
-
-    def safe_call(self, command):
-        """Cross-platform command-line check."""
-        while True:
-            try:
-                return call(command, shell=True, stdout=PIPE)
-            except OSError as e:
-                if e.errno == errno.EINTR:
-                    continue
-                else:
-                    raise
-
     def hide_main_window(self):
         if self.isVisible():
             self.hide()