Text missing when render pdf into image

[scegg]

PDFtoImage version

3.0.0

OS

Windows

OS version

No response

Architecture

x64

Framework

.NET (Core)

App framework

No response

Detailed bug report

using (var pdfStream = File.OpenRead(pdfFile))
            {
                PDFtoImage.Conversion.SavePng("D:\\output.png", pdfStream);
            }

1.pdf When processing the pdf attached, all texts are missing in the lower part of the image created. Png file is too big to upload.

[scegg]

The lower part of PNG:

[sungaila]

Hi @scegg, I can confirm the lower part of the PDF is not rendered correctly. I'll be looking into this issue.

[sungaila]

It looks like a memory issue. Your PDF is rendered at 300 DPI (default values) and is 4,000 * 46,812 in size.

That makes (4,000 46,812) px 4 bytes/px = 748,992,000 bytes ≈ 749 megabytes.

If you lower the DPI the text renders properly again:

using (var pdfStream = File.OpenRead(pdfFile))
{
    PDFtoImage.Conversion.SavePng("D:\\output.png", pdfStream, dpi: 200);
}

I'll check if there are options in PDFium or SkiaSharp to circumvent this memory issue.

[scegg]

Thanks for your testing. Waiting for further result.

There is no memory related, actually none at all, exception thrown. In this situation, the code should throw some instead of generating a corrupted file.

[sungaila]

I agree with you that an Exception should be thrown instead of generating corrupted images. However, this library is a wrapper of SkiaSharp and PDFium so there is little I can do about this.

For testing I replaced SkiaSharp with System.Common.Drawing (GDI) but the font issue is still there. This confirms that the issue must be related to PDFium.

Right now I am checking if there is any workaround or setting to fix this issue in PDFium.

[sungaila]

Unfortunately, I haven't found a way to work around this issue or detecting it in the first place.

[sungaila]

@scegg Good news: I did find a workaround after all! You can use the optional parameter UseTiling to render your sample PDF properly (text isn't missing anymore).

using (var pdfStream = File.OpenRead(pdfFile))
{
    PDFtoImage.Conversion.SavePng("D:\\output.png", pdfStream, options: new(UseTiling: true));
}

With this parameter, the PDF is rendered in several parts and combined into one complete image at the end. This circumvents the issue of PDFium failing at very high resolutions.