improve large image printing

images longer than 1024 pixels will be split into multiple fragments.

src/escpos/escpos.py

@@ -56,7 +56,8 @@ class Escpos(object):
         """
         pass
 
-    def image(self, img_source, high_density_vertical=True, high_density_horizontal=True, impl="bitImageRaster"):
+    def image(self, img_source, high_density_vertical=True, high_density_horizontal=True, impl="bitImageRaster",
+              fragment_height=1024):
         """ Print an image
 
         You can select whether the printer should print in high density or not. The default value is high density.
@@ -76,9 +77,20 @@ class Escpos(object):
         :param high_density_vertical: print in high density in vertical direction *default:* True
         :param high_density_horizontal: print in high density in horizontal direction *default:* True
         :param impl: choose image printing mode between `bitImageRaster`, `graphics` or `bitImageColumn`
+        :param fragment_height: Images larger than this will be split into multiple fragments *default:* 1024
 
         """       
         im = EscposImage(img_source)
+
+        if im.height > fragment_height:
+            fragments = im.split(fragment_height)
+            for fragment in fragments:
+                self.image(fragment,
+                           high_density_vertical=high_density_vertical,
+                           high_density_horizontal=high_density_horizontal,
+                           impl=impl,
+                           fragment_height=fragment_height)
+            return
         
         if impl == "bitImageRaster":
             # GS v 0, raster format bit image

src/escpos/image.py

@@ -8,6 +8,12 @@ This module contains the image format handler :py:class:`EscposImage`.
 :license: GNU GPL v3
 """
 
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+from __future__ import unicode_literals
+
+import math
 from PIL import Image, ImageOps
 
 
@@ -30,6 +36,9 @@ class EscposImage(object):
         else:
             img_original = Image.open(img_source)
 
+        # store image for eventual further processing (splitting)
+        self.img_original = img_original
+
         # Convert to white RGB background, paste over white background
         # to strip alpha.
         img_original = img_original.convert('RGBA')
@@ -88,3 +97,21 @@ class EscposImage(object):
         Convert image to raster-format binary
         """
         return self._im.tobytes()
+
+    def split(self, fragment_height):
+        """
+        Split an image into multiple fragments after fragment_height pixels
+
+        :param fragment_height: height of fragment
+        :return: list of PIL objects
+        """
+        passes = int(math.ceil(self.height/fragment_height))
+        fragments = []
+        for n in range(0, passes):
+            left = 0
+            right = self.width
+            upper = n * fragment_height
+            lower = min((n + 1) * fragment_height, self.height)
+            box = (left, upper, right, lower)
+            fragments.append(self.img_original.crop(box))
+        return fragments