Use pylibdmtx for datamatrix generation

requirements.txt

@@ -22,7 +22,6 @@ pdfrw
 reportlab
 Wand
 Pillow  # also scan processing
-pyStrich  # TODO: can we replace this with stuff from pylibdmtx?
 
 # Scan processing
 opencv-python

zesje/pdf_generation.py

-from io import BytesIO
 from tempfile import NamedTemporaryFile
 
 import PIL
 from pdfrw import PdfReader, PdfWriter, PageMerge
-from pystrich.datamatrix import DataMatrixEncoder
+from pylibdmtx.pylibdmtx import encode
 from reportlab.lib.units import mm
 from reportlab.pdfgen import canvas
 
@@ -16,9 +15,9 @@ def generate_pdfs(exam_pdf_file, exam_id, copy_nums, output_paths, id_grid_x,
     """
     Generate the final PDFs from the original exam PDF.
 
-    To maintain a consistent size of the DataMatrix codes, adhere to (# of
-    letters in exam ID) + 2 * (# of digits in exam ID) = C for a certain
-    constant C. The reason for this is that pyStrich encodes two digits in as
+    To maintain a consistent grid size of the DataMatrix codes, adhere to
+    (# of letters in exam ID) + 2 * (# of digits in exam ID) = C for a certain
+    constant C. The reason for this is that libdmtx encodes two digits in as
     much space as one letter.
 
     If maximum interchangeability with version 1 QR codes is desired (error
@@ -155,9 +154,9 @@ def generate_datamatrix(exam_id, page_num, copy_num):
     """
     Generates a DataMatrix code to be used on a page.
 
-    To maintain a consistent size of the DataMatrix codes, adhere to (# of
-    letters in exam ID) + 2 * (# of digits in exam ID) = C for a certain
-    constant C. The reason for this is that pyStrich encodes two digits in as
+    To maintain a consistent grid size of the DataMatrix codes, adhere to
+    (# of letters in exam ID) + 2 * (# of digits in exam ID) = C for a certain
+    constant C. The reason for this is that pylibdmtx encodes two digits in as
     much space as one letter.
 
     If maximum interchangeability with version 1 QR codes is desired (error
@@ -182,8 +181,10 @@ def generate_datamatrix(exam_id, page_num, copy_num):
 
     data = f'{exam_id}/{copy_num:04d}/{page_num:02d}'
 
-    image_bytes = DataMatrixEncoder(data).get_imagedata(cellsize=2)
-    return PIL.Image.open(BytesIO(image_bytes))
+    encoded = encode(data.encode('utf-8'), size='18x18')
+    datamatrix = PIL.Image.frombytes('RGB', (encoded.width, encoded.height), encoded.pixels)
+    datamatrix = datamatrix.resize((44, 44)).convert('L')
+    return datamatrix
 
 
 def _generate_overlay(canv, pagesize, exam_id, copy_num, num_pages, id_grid_x,
@@ -192,9 +193,9 @@ def _generate_overlay(canv, pagesize, exam_id, copy_num, num_pages, id_grid_x,
     Generates an overlay ('watermark') PDF, which can then be overlaid onto
     the exam PDF.
 
-    To maintain a consistent size of the DataMatrix codes in the overlay,
+    To maintain a consistent grid size of the DataMatrix codes in the overlay,
     adhere to (# of letters in exam ID) + 2 * (# of digits in exam ID) = C for
-    a certain constant C. The reason for this is that pyStrich encodes two
+    a certain constant C. The reason for this is that pylibdmtx encodes two
     digits in as much space as one letter.
 
     If maximum interchangeability with version 1 QR codes is desired (error