PDF to Image Custom Encoding

In this guide rendering pdf document to image using custom encoding will be shown.

Before you begin #

You should get your API key from your UniCloud account.

If this is your first time using UniPDF SDK, follow this guide to set up a local development environment.

Project setup #

Clone the project repository #

In your terminal, clone examples repository. It contains the Go code we will be using for this guide.

git clone https://github.com/unidoc/unipdf-examples.git

Navigate to the render folder in the unipdf-examples directory.

cd unipdf-examples/render

Configure environment variables #

Replace the UNIDOC_LICENSE_API_KEY with your API credentials from your UniCloud account.

Linux/Mac #

export UNIDOC_LICENSE_API_KEY=PUT_YOUR_API_KEY_HERE

Windows #

set UNIDOC_LICENSE_API_KEY=PUT_YOUR_API_KEY_HERE

How it works #

The import section imports unipdf packages and other necessary libraries.

The init function in lines 26-33 loads your metred API key and authenticates your request with UNIDOC_LICENSE_API_KEY.

The main function in lines 35-92 reads the pdf files in the given directory and renders each page of each pdf file to image using the custom JPX encoder given in lib_jpeg2k_encoder.go.

lines 36-39 validates the minimum number of environment variables. Line 40 gets the output directory using os.Args[1]. lines 42-44 checks if the output directory exists and it creates a new directory if it doesn’t exist. The loop in lines 46-91 iterates through all the files given in the environment variable and runs render operation on each file.

The custom encoder is registered in lines 64-65 using

customJpxEncoder := jpeg2k.NewCustomJPXEncoder()
core.RegisterCustomStreamEncoder(core.StreamEncodingFilterNameJPX, customJpxEncoder)

In line 56 an image device is instantiated using render.NewImageDevice(). The inner loop in lines 57-77 iterates through each page and converts it to an image.

Run the code #

Run the code using the following code, where OUTPUT_DIR directory is the directory to save the output to and INPUT.pdf... represents a list of pdf files to be rendered to an image using the custom encoding.

go run pdf_image_render_custom_encoder_cgo.go OUTPUT_DIR INPUT.pdf...

After running the code all images generated by the code will be available in the OUTPUT_DIR provided.