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GroupDocs.Signature provides PreviewSignatureOptions class to generate an image of a signature before it is placed on a document - for example, to show a user what a text, barcode or QR code signature will look like.
Here are the steps to generate signature preview with GroupDocs.Signature:
- Create the sign options that describe the signature, for example TextSignOptions or QrCodeSignOptions. No document is needed.
- Instantiate the PreviewSignatureOptions object with:
- the sign options;
- a function that creates the stream for the signature image (see CreateSignatureStream);
- image preview format - PNG / JPEG / BMP / GIF / SVG (PNG by default),
- an optional
signature_idthat tells the functions which signature they are handling.
The stream returned by the create function is closed automatically as soon as the signature image is written: a file is closed, and an io.BytesIO already holds the complete image. If you need to process the finished image or clean up resources yourself, pass a release function as an additional argument (see ReleaseSignatureStream).
- Call the static
generate_signature_previewmethod of Signature class and pass PreviewSignatureOptions to it.
GroupDocs.Signature calls the create function with the PreviewSignatureOptions object and writes the signature image into the stream it returns: a writable file object, an io.BytesIO, or a .NET stream.
def create_signature_stream(preview_options):
# Name the image after the signature_id set on the preview options
return open(f"{preview_options.signature_id}.png", "wb")
The release function receives the same preview options and the same object the create function returned. By the time it is called, the image is complete.
def release_signature_stream(preview_options, signature_stream):
# signature_stream is the object create_signature_stream returned
print(f"Image file {signature_stream.name} is ready for preview")
from groupdocs.signature import Signature
from groupdocs.pydrawing import Color
from groupdocs.signature.domain import SignatureFont
from groupdocs.signature.options import PreviewSignatureOptions, TextSignOptions
def create_signature_stream(preview_options):
# Name the image after the signature_id set below
return open(f"{preview_options.signature_id}.png", "wb")
def release_signature_stream(preview_options, signature_stream):
print(f"Image file {signature_stream.name} is ready for preview")
def generate_signature_preview_to_file():
# Describe the signature exactly as you would for signing
sign_options = TextSignOptions("John Smith")
sign_options.width = 200
sign_options.height = 50
sign_options.fore_color = Color.dark_blue
font = SignatureFont()
font.family_name = "Arial"
font.size = 24
sign_options.font = font
# Create preview options object
preview_options = PreviewSignatureOptions(sign_options, create_signature_stream, release_signature_stream)
preview_options.signature_id = "text_signature"
preview_options.preview_format = PreviewSignatureOptions.PreviewFormats.PNG
# Generate preview; no document is involved
Signature.generate_signature_preview(preview_options)
if __name__ == "__main__":
generate_signature_preview_to_file()
Binary file (PNG, 983 bytes)
The create function can return an io.BytesIO. When generate_signature_preview returns, the buffer holds the whole image, ready to be stored or sent elsewhere.
import io
from groupdocs.signature import Signature
from groupdocs.signature.domain import QrCodeTypes
from groupdocs.signature.options import PreviewSignatureOptions, QrCodeSignOptions
def generate_signature_preview_to_memory():
image = io.BytesIO()
def create_signature_stream(preview_options):
# Write the image into the buffer instead of a file
return image
sign_options = QrCodeSignOptions("https://www.groupdocs.com/", QrCodeTypes.QR)
sign_options.width = 120
sign_options.height = 120
preview_options = PreviewSignatureOptions(sign_options, create_signature_stream)
Signature.generate_signature_preview(preview_options)
data = image.getvalue()
is_png = data.startswith(b"\x89PNG")
print(f"QR code preview: {len(data)} bytes, PNG image: {is_png}")
if __name__ == "__main__":
generate_signature_preview_to_memory()
QR code preview: 918 bytes, PNG image: True
One pair of functions can serve any number of previews: signature_id tells them which signature they are handling, and preview_format chooses the image type. Without a license, the SVG format is available only for Code39 barcodes.
from groupdocs.signature import Signature
from groupdocs.signature.domain import BarcodeTypes, QrCodeTypes
from groupdocs.signature.options import BarcodeSignOptions, PreviewSignatureOptions, QrCodeSignOptions
FORMATS = PreviewSignatureOptions.PreviewFormats
def create_signature_stream(preview_options):
extension = preview_options.preview_format.name.lower()
return open(f"{preview_options.signature_id}.{extension}", "wb")
def release_signature_stream(preview_options, signature_stream):
print(f"{preview_options.signature_id}: {signature_stream.name}")
def generate_signature_previews_in_different_formats():
signatures = [
("barcode", BarcodeSignOptions("123456789012", BarcodeTypes.CODE128), FORMATS.JPEG),
("qr_code", QrCodeSignOptions("https://www.groupdocs.com/", QrCodeTypes.QR), FORMATS.GIF),
("barcode_vector", BarcodeSignOptions("GROUPDOCS", BarcodeTypes.CODE39), FORMATS.SVG),
]
for signature_id, sign_options, preview_format in signatures:
preview_options = PreviewSignatureOptions(sign_options, create_signature_stream, release_signature_stream)
preview_options.signature_id = signature_id
preview_options.preview_format = preview_format
Signature.generate_signature_preview(preview_options)
if __name__ == "__main__":
generate_signature_previews_in_different_formats()
barcode.jpeg (8 KB)
barcode_vector.svg (3 KB)
qr_code.gif (4 KB)
You may easily run the code above and see the feature in action in our GitHub examples:
Along with the full-featured Python library, we provide simple but powerful free online apps.
To sign PDF, Word, Excel, PowerPoint, and other documents you can use the online apps from the GroupDocs.Signature App Product Family.
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