Question

I’m currently attempting to generate thumbnails of PDFs using Ghostscript (or more specifically GhostscriptSharp, the C# wrapper version) and have run into some issues with the image quality that is being output.

Using the following method:

GeneratePageThumbs(string inputPath, string outputPath, int firstPage, int lastPage, int width, int height)

and changing the width and height to smaller numbers that will generate a thumbnail roughly the size that I am looking for, for example a height of 12 and width of 8 will generate a set of thumbnails with the size of 102 x 88 pixels.

Ideally – I am trying to generate thumbnails with a size of 100 x 80 that look reasonably well when rendered as HTML (in an image tag) so that the reader could get a decent idea of what they are looking at from a thumbnail (as it is currently completely unreadable)

These are the current settings (from the C# wrapper):

private static readonly string[] ARGS = new string[] {
     // Keep gs from writing information to standard output
     "-q",                     
     "-dQUIET",

     "-dPARANOIDSAFER",         // Run this command in safe mode
     "-dBATCH",                 // Keep gs from going into interactive mode
     "-dNOPAUSE",               // Do not prompt and pause for each page
     "-dNOPROMPT",              // Disable prompts for user interaction           
     "-dMaxBitmap=500000000",   // Set high for better performance
     "-dNumRenderingThreads=4", // Multi-core, come-on!

     // Configure the output anti-aliasing, resolution, etc
     "-dAlignToPixels=0",
     "-dGridFitTT=0",
     "-dTextAlphaBits=4",
     "-dGraphicsAlphaBits=4"
};

However – I am not very familiar with Ghostsharp and its settings to strike a balance between size and quality. I wouldn’t be opposed to creating larger images and scaling them for the thumbnails, although I would prefer to get the thumbnails to work if possible.

Answer 1

Without seeing the original documents I can’t be sure, but it seems unlikely to me that 102×88 pixels is going to be sufficient to create readable text.

The TextAlphaBits is probably too large for this size, all you will get is a blur. Try not setting TextAlphaBits at all. NumRenderingThreads won’t do anything useful with a page this small (though it won’t do any harm either).