golang pdf to png

With the advent of the digital age, more and more files are being converted into electronic documents, of which PDF files are the most commonly used. The reading experience of PDF files is more friendly than other file formats, but in some specific scenarios, the conversion of PDF files is also necessary, such as converting PDF files to PNG image format.

In the Golang programming language, there are many ways to achieve the PDF to PNG function. These methods are usually implemented based on different third-party libraries. This article will introduce some of the more commonly used methods.

Method 1: Using Ghostscript and ImageMagick

Ghostscript is a cross-platform PostScript and PDF interpreter that can convert PostScript or PDF files into image files in a variety of formats. ImageMagick is a powerful image processing tool that can handle a variety of image formats. By combining Ghostscript and ImageMagick, we can achieve the PDF to PNG function.

First, we need to execute the following command in the command line to install Ghostscript and ImageMagick:

sudo apt install ghostscript imagemagick

Then, in the Golang code, we can execute the following in the command line through the os.Exec function Command to convert PDF to PNG:

cmd := exec.Command(
  "bash",
  "-c",
  fmt.Sprintf("gs -sDEVICE=pngalpha -r72 -o - %s | convert - %s.png", pdfFilePath, pngFilePath),
)
err := cmd.Run()

In the above code, we use Ghostscript to convert the PDF file into a PNG stream, and then use ImageMagick to convert the PNG stream into a PNG file. Among them, the parameter -sDEVICE=pngalpha of the gs command means to output an image in PNG format, -r72 means to set the resolution to 72dpi, and -o means to output to the standard output stream.

Method 2: Use GoFPDF library and rsvg-convert

GoFPDF is a modular PDF document generation library based on FPDF and UFPDF, which can be used to create and manipulate PDF files. rsvg-convert is a command-line tool based on the rsvg library that can convert SVG files into various image formats. By combining GoFPDF and rsvg-convert, we can achieve the PDF to PNG function.

First, we need to execute the following command in the command line to install rsvg-convert:

sudo apt install librsvg2-bin

Then, in the Golang code, we can use GoFPDF to read the PDF file and convert it For SVG files, the code is as follows:

pdfReader := gofpdf.New("P", "mm", "A4", "")
pdfReader.SetSourceFile(pdfFile)

var buf bytes.Buffer
for i := 1; i <= pdfReader.GetPageCount(); i++ {
  tpl := pdfReader.ImportPage(i)
  opt := gofpdf.ImageOptions{}
  svg, err := tpl.ToSVG(&opt)
  if err != nil {
    return err
  }
  buf.Write(svg)
}

svgData := buf.Bytes()
svgFile, err := os.Create(svgFilePath)
if err != nil {
  return err
}
defer svgFile.Close()

_, err = svgFile.Write(svgData)
if err != nil {
  return err
}

In the above code, we use gofpdf.ImportPage to convert each page of the PDF file into a template (Template), and then use the ToSVG ​​method to convert each template into an SVG file. , and merge multiple SVG files into one file and save it locally. It should be noted that the parameter opt of gofpdf.ToSVG ​​is a gofpdf.ImageOptions structure, which contains some configuration information of the converted SVG image.

Next, we can use the rsvg-convert command to convert the SVG file into a PNG file. The code is as follows:

cmd := exec.Command(
  "bash",
  "-c",
  fmt.Sprintf("rsvg-convert -f png -o %s %s", pngFilePath, svgFilePath),
)
err := cmd.Run()

In the above code, we use the rsvg-convert command to convert the SVG file into PNG file and save it in the local file system.

Method 3: Use UniDoc library

UniDoc is a powerful Golang library for PDF files and other document types, supporting various PDF operations, including PDF to PNG. UniDoc uses Ghostscript to convert PDF to PNG.

The code using UniDoc is as follows:

pdfReader, err := unipdf.NewPdfReaderFromFile(pdfFilePath)
if err != nil {
  log.Fatalf("Error: %v", err)
}

numPages, err := pdfReader.GetNumPages()
if err != nil {
  log.Fatalf("Error: %v", err)
}

for i := 1; i <= numPages; i++ {
  page, err := pdfReader.GetPageAsImg(i)
  if err != nil {
    log.Fatalf("Error: %v", err)
  }

  pngFile, err := os.Create(pngFilePath)
  defer pngFile.Close()

  if err := png.Encode(pngFile, page); err != nil {
    log.Fatalf("Error: %v", err)
  }
}

In the above code, we use UniDoc's GetPageAsImg method to convert each page of the PDF file into an Image type containing image data, and then use Golang's built-in The png library converts the Image type into a PNG file and saves it to the local disk.

Summary:

Among the above three methods, for the method based on Ghostscript and ImageMagick and the method based on the GoFPDF library and rsvg-convert tool, we need to install the relevant tools in the command line first. , and then use the os.Exec function in the Golang code to execute the corresponding command. For methods based on the UniDoc library, we only need to import the UniDoc library and use the related methods in it.

To sum up, in addition to Golang’s own PNG library, the above three methods all use third-party libraries or command line tools to implement the PDF to PNG function. When choosing a specific implementation method, we can choose based on project needs and the characteristics of our own technology stack.

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