Python、JSignature 和 ReportLab

Question

I'm looking to write a signature to PDF. I'm using JSignature and Reportlab. My code works successfully for writing the data to a file and the database. I just cannot figure out how to write the signature to the canvas. Has anyone passed the signature into the canvas successfully?

Thank you in advance.

Here's a look at my code:

pdf.py

import io
from django.core.files.base import ContentFile
from reportlab.lib.units import inch
from reportlab.pdfgen import canvas
from reportlab.lib.utils import ImageReader


def create_pdf(parent):
    # create a file-like buffer to receive PDF data
    buffer = io.BytesIO()

    # create the pdf object, using the buffer as its "file"
    p = canvas.Canvas(buffer)
    # create text
    textobject = p.beginText()
    # start text at top left of page
    textobject.setTextOrigin(inch, 11*inch)
    # set font and size
    textobject.setFont("Helvetica-Bold", 18)
    textobject.textLine("My Document")
    textobject.textLine("")

    # write page 1
    textobject.setFont("Helvetica", 12)

    p_name = f'Name: {participant.first_name} {participant.middle_initial} {participant.last_name}'
    textobject.textLine(p_name)

    sig = f'Signature:'
    textobject.textLine(sig)

----insert signature here----


    # write created text to canvas
    p.drawText(textobject)
    # close the pdf canvas
    p.showPage()
    p.save()

    buffer.seek(0)
    # get content of buffer
    pdf_data = buffer.getvalue()
    # save to django File object
    file_data = ContentFile(pdf_data)
    # name the file
    file_data.name = f'{participant.last_name}.pdf'
    # 
    participant.pdf = file_data
    participant.save()

    

Model:

class Participant(models.Model):

    first_name = models.CharField(max_length=50)
    middle_initial = models.CharField(max_length=50, blank=True)
    last_name = models.CharField(max_length=50, blank=True)
    signature = JSignatureField()
    pdf = models.FileField(blank=True, null=True)

Answer 1

For those interested in how I was able to get this functioning. The primary issue was The image would be completely black when pulling it into the PDF. Here's what is required:

In your View:

• Use the Jsignature draw_signature function and get the image:

rsr_image = draw_signature(signature)

• save the signature as a PNG and then store

            # save signature as png to prevent darkening, save to model
            rsr_file_name = str(new_parent.id)+'_rsr.png'
            buffer = BytesIO()
            rsr_image.save(buffer, 'PNG')
            new_parent.rsr_image.save(rsr_file_name, File(buffer))

Create the following function, in order to…

• Open the image, create a new background for the image, and save it.

def get_jpeg_image(new_parent):
    # open png image
    png_image = Image.open(new_parent.rsr_image)
    # create new image with 'RGB' mode which is compatible with jpeg,
    # with same size as old and with white(255,255,255) background
    bg = Image.new("RGB", png_image.size, (255, 255, 255))
    # paste old image pixels in new background
    bg.paste(png_image, png_image)
    # give image file name
    file_name_jpeg = str(new_parent.id)+'.jpg'
    bg.save(file_name_jpeg)
    return file_name_jpeg

Reference that function inside your create PDF function to convert the PNG to JPG

jpeg_image = get_jpeg_image(participant)
   

Hope this helps someone.