如何为PyZbar添加Pharmacode支持？制药标签检测应用需求

Great question—since PyZbar is just a Python wrapper for the zbar library, adding Pharmacode support means either extending the underlying zbar code (the more involved path) or combining PyZbar with a separate Pharmacode decoder (the quicker workaround). Let's break down both approaches:

PyZbar doesn't handle Pharmacode because the base zbar library doesn't include it by default. Here's how to fix that:

• Step 1: Get zbar's source code
  Grab the latest zbar source from its repository. Look for the barcode decoding modules (usually in src/decoder/). You'll need to add a new decoder for Pharmacode.

• Step 2: Implement Pharmacode decoding logic
  Pharmacode (specifically the Pharmaceutical Binary Code) uses variable-width bars to encode numeric values. The core rule is:

  • Narrow bars represent 0, wide bars represent 1 (or vice versa, depending on the variant)
  • The sequence of bars translates directly to a binary number, which you convert to decimal.
    You'll need to write C code that detects the bar widths, parses the binary sequence, and returns the decoded value. Add this as a new decoder in zbar's codebase, making sure to register it alongside other barcodes like Code 128 or QR.

• Step 3: Compile the modified zbar library
  Build zbar from your modified source to generate updated shared libraries (.so on Linux, .dll on Windows, .dylib on macOS).

• Step 4: Rebuild PyZbar to link against your custom zbar
  Clone the PyZbar repository, adjust the setup scripts to point to your compiled zbar library, then build and install the modified PyZbar package. Now your PyZbar calls will include Pharmacode detection.

If you don't want to mess with C compilation, you can use PyZbar for the batch number (which it handles well) and use a separate method for Pharmacode:

• Sub-option A: Use a Python library that supports Pharmacode
  Libraries like pyzxing (a wrapper for ZXing) can decode Pharmacode. You can run PyZbar to grab the batch number, then pass the same image to pyzxing to get the Pharmacode value. Example snippet:

  import cv2
  from pyzbar.pyzbar import decode
  from pyzxing import BarCodeReader
  
  img = cv2.imread("pharm_label.jpg")
  # Get batch number with PyZbar
  batch_results = decode(img)
  batch_number = [res.data.decode('utf-8') for res in batch_results if res.type == "CODE128"][0]
  
  # Get Pharmacode with pyzxing
  reader = BarCodeReader()
  pharmacode_results = reader.decode(img)
  pharmacode = pharmacode_results[0]['raw']
  

• Sub-option B: Implement a basic Pharmacode decoder yourself
  If you want full control, use OpenCV to preprocess the image and parse the bar widths:

  1. Convert the image to grayscale and apply thresholding to get a binary image.
  2. Crop or isolate the Pharmacode region (you can use contour detection in OpenCV to find it).
  3. Scan the barcode horizontally to measure the width of each black/white bar.
  4. Classify each bar as "narrow" or "wide" (using a threshold based on the average narrow bar width).
  5. Convert the sequence of narrow/wide bars to a binary number, then to the final Pharmacode value.

  Here's a rough outline of the parsing logic:

  def decode_pharmacode(bar_widths):
      # Assume narrow bars are 1 unit, wide are 2 units (adjust based on your labels)
      threshold = sum(bar_widths) / len(bar_widths) * 1.5
      binary_str = ""
      # Iterate over bar widths, skipping the first/last quiet zones if needed
      for width in bar_widths[1:-1]:
          if width > threshold:
              binary_str += "1"
          else:
              binary_str += "0"
      # Convert binary to decimal (Pharmacode is usually a positive integer)
      return int(binary_str, 2)
  

• Image Preprocessing is Critical: No matter which approach you take, use OpenCV to clean up the image first—resize, denoise, adjust contrast, and threshold to make the barcode lines sharp. This will drastically improve decoding accuracy.
• Pharmacode Variants: Double-check which Pharmacode variant your labels use (there's also a two-track version, though single-track is more common for pharmaceutical labels) to make sure your decoder matches the spec.

内容的提问来源于stack exchange，提问作者Tarek Tabba