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GroupDocs.Signature provides PreviewOptions class to specify different options to manage document pages preview generation process. The feature also supports archives previewing.
Here are the steps to generate document preview with GroupDocs.Signature:
- Create new instance of Signature class and pass source document path or stream as a constructor parameter.
- Instantiate the PreviewOptions object with:
- a function that creates a stream for each page image (see CreateDocPageStream);
- image preview format - PNG / JPEG / BMP,
- page numbers to process;
- custom resolution of preview images (if needed).
The stream returned by the create function is closed automatically as soon as the page image is written: a file is closed, and an io.BytesIO already holds the complete image. If you need to process each finished image or clean up resources yourself, pass a release function as an additional argument (see ReleaseDocPageStream).
- Call
generate_previewmethod of Signature class instance and pass PreviewOptions to it.
GroupDocs.Signature calls the create function once for each page and writes the page image into the stream it returns: a writable file object, an io.BytesIO, or a .NET stream. The page_data argument is a PreviewPageData object with the page_number, the file_name of the document and the preview_format.
Page numbers are 0-based: page_data.page_number is 0 for the first page of the document.
def create_page_stream(page_data):
# 0-based: preview_page_0.png is the first page
return open(f"preview_page_{page_data.page_number}.png", "wb")
When you preview an archive, the function is called for the pages of every document in it. Page numbers start at 0 again for each document, so use page_data.file_name as well when you name the images.
The release function receives the same page_data and the same object the create function returned. By the time it is called, the image is complete.
def release_page_stream(page_data, page_stream):
# page_stream is the object create_page_stream returned
print(f"Image file {page_stream.name} is ready for preview")
from groupdocs.signature import Signature
from groupdocs.signature.options import PreviewOptions
def create_page_stream(page_data):
# Page numbers are 0-based: preview_page_0.png is the first page
image_name = f"preview_page_{page_data.page_number}.png"
print(f"Saving page {page_data.page_number + 1} to {image_name}")
return open(image_name, "wb")
def generate_document_preview():
with Signature("sample.pdf") as signature:
# Create preview options object: one PNG image per page
preview_options = PreviewOptions(create_page_stream)
preview_options.preview_format = PreviewOptions.PreviewFormats.PNG
# Generate preview
signature.generate_preview(preview_options)
if __name__ == "__main__":
generate_document_preview()
sample.pdf is the sample file used in this example. Click here to download it.
preview_page_0.png (75 KB)
preview_page_1.png (64 KB)
This example reads the document from a stream and keeps the page images in memory: the create function returns an io.BytesIO, and the release function receives it filled with the complete image.
import io
from groupdocs.signature import Signature
from groupdocs.signature.options import PreviewOptions
def create_page_stream(page_data):
# Keep each page image in memory instead of writing a file
return io.BytesIO()
def release_page_stream(page_data, page_stream):
# page_stream is the BytesIO returned above, already holding the whole image
image = page_stream.getvalue()
print(f"Page {page_data.page_number}: {len(image)} bytes of JPEG")
def generate_document_preview_from_stream():
with open("sample.pdf", "rb") as stream:
with Signature(stream) as signature:
# Create preview options object with both functions
preview_options = PreviewOptions(create_page_stream, release_page_stream)
preview_options.preview_format = PreviewOptions.PreviewFormats.JPEG
# Generate preview
signature.generate_preview(preview_options)
if __name__ == "__main__":
generate_document_preview_from_stream()
sample.pdf is the sample file used in this example. Click here to download it.
Page 0: 276044 bytes of JPEG
Page 1: 224194 bytes of JPEG
Set page_numbers to preview only some pages. The numbers are 0-based, so [1] selects the second page.
from groupdocs.signature import Signature
from groupdocs.signature.options import PreviewOptions
def create_page_stream(page_data):
return open(f"preview_page_{page_data.page_number}.png", "wb")
def release_page_stream(page_data, page_stream):
print(f"Image file {page_stream.name} is ready for preview")
def generate_document_preview_of_selected_pages():
with Signature("sample.pdf") as signature:
preview_options = PreviewOptions(create_page_stream, release_page_stream)
# Page numbers are 0-based: [1] is the second page
preview_options.page_numbers = [1]
signature.generate_preview(preview_options)
if __name__ == "__main__":
generate_document_preview_of_selected_pages()
sample.pdf is the sample file used in this example. Click here to download it.
Binary file (PNG, 64 KB)
The default resolution is 96 DPI. Pass the resolution as the third argument of PreviewOptions, or set the resolution property.
from groupdocs.signature import Signature
from groupdocs.signature.options import PreviewOptions
def create_page_stream(page_data):
return open(f"preview_page_{page_data.page_number}_150dpi.jpg", "wb")
def release_page_stream(page_data, page_stream):
print(f"Image file {page_stream.name} is ready for preview")
def generate_document_preview_with_resolution():
with Signature("sample.pdf") as signature:
resolution = 150
# Create preview options object: 150 DPI instead of the default 96
preview_options = PreviewOptions(create_page_stream, release_page_stream, resolution)
preview_options.preview_format = PreviewOptions.PreviewFormats.JPEG
# Generate preview
signature.generate_preview(preview_options)
if __name__ == "__main__":
generate_document_preview_with_resolution()
sample.pdf is the sample file used in this example. Click here to download it.
preview_page_0_150dpi.jpg (495 KB)
preview_page_1_150dpi.jpg (425 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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