Merge pull request #152 from python-escpos/fix/large-image-printing

Fix/large image printing

doc/user/usage.rst

@@ -204,6 +204,37 @@ Here you can download an example, that will print a set of common barcodes:
 
     * :download:`barcode.bin </download/barcode.bin>` by `@mike42 <https://github.com/mike42>`_
 
+Hint: preprocess printing
+-------------------------
+
+Printing images directly to the printer is rather slow.
+One factor that slows down the process is the transmission over e.g. serial port.
+
+Apart from configuring your printer to use the maximum baudrate (in the case of serial-printers), there is not much
+that you can do.
+However you could use the :py:class:`escpos.printer.Dummy`-printer to preprocess your image.
+This is probably best explained by an example:
+
+.. code-block:: Python
+
+   from escpos.printer import Serial, Dummy
+
+   p = Serial()
+   d = Dummy()
+
+   # create ESC/POS for the print job, this should go really fast
+   d.text("This is my image:\n")
+   d.image("funny_cat.png")
+   d.cut()
+
+   # send code to printer
+   p._raw(d.output)
+
+This way you could also store the code in a file and print later.
+You could then for example print the code from another process than your main-program and thus reduce the waiting time.
+(Of course this will not make the printer print faster.)
+
+
 How to update your code for USB printers
 ----------------------------------------
 

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