Question

在下面的示例中，我们将该gographics/imagick包用作ImageMagick的C库的包装，以将我们的PDF转换为JPG。处理过程如下：我们使用软件包将测试文件加载到测试文件中，然后通过设置分辨率，压缩级别和alpha通道设置进行处理，然后保存最终的输出文件。由于该库基于C构建，因此重要的是我们必须适当调用Terminate和Destroy函数以检查内存使用情况。

在Ubuntu 18.04下运行的前提条件：

    sudo apt install libmagic-dev libmagickwand-dev

代码：

package main

import (
    "log"
    "gopkg.in/gographics/imagick.v2/imagick"
)

func main() {

    pdfName := "ref.pdf"
    imageName := "test.jpg"

    if err := ConvertPdfToJpg(pdfName, imageName); err != nil {
        log.Fatal(err)
    }
}

// ConvertPdfToJpg will take a filename of a pdf file and convert the file into an 
// image which will be saved back to the same location. It will save the image as a 
// high resolution jpg file with minimal compression.
func ConvertPdfToJpg(pdfName string, imageName string) error {

    // Setup
    imagick.Initialize()
    defer imagick.Terminate()

    mw := imagick.NewMagickWand()
    defer mw.Destroy()

    // Must be *before* ReadImageFile
    // Make sure our image is high quality
    if err := mw.SetResolution(300, 300); err != nil {
        return err
    }

    // Load the image file into imagick
    if err := mw.ReadImage(pdfName); err != nil {
        return err
    }

    // Must be *after* ReadImageFile
    // Flatten image and remove alpha channel, to prevent alpha turning black in jpg
    if err := mw.SetImageAlphaChannel(imagick.ALPHA_CHANNEL_FLATTEN); err != nil {
        return err
    }

    // Set any compression (100 = max quality)
    if err := mw.SetCompressionQuality(95); err != nil {
        return err
    }

    // Select only first page of pdf
    mw.SetIteratorIndex(0)

    // Convert into JPG
    if err := mw.SetFormat("jpg"); err != nil {
        return err
    }

    // Save File
    return mw.WriteImage(imageName)
}

如果您看到类似以下的错误，请参阅指南。

    ERROR_POLICY: not authorized `TestPdf.pdf' @ error/constitute.c/ReadImage/412