Unable to get deskew angle?

[Oninaig]

When processing an image with the sample code provided in the project:

var settings = new MagickReadSettings();
// Settings the density to 300 dpi will create an image with a better quality
settings.Density = new Density(300, 300);

using (var images = new MagickImageCollection())
{
    // Add all the pages of the pdf file to the collection
    images.Read("Snakeware.pdf", settings);

    var page = 1;
    foreach (var image in images)
    {
        // Write page to file that contains the page number
        image.Write("Snakeware.Page" + page + ".png");
        // Writing to a specific format works the same as for a single image
        image.Format = MagickFormat.Ptif;
        image.Write("Snakeware.Page" + page + ".tif");
        page++;
    }
}

If I modify this code to try to get the deskew angle during the conversion:

var settings = new MagickReadSettings();
// Settings the density to 300 dpi will create an image with a better quality
settings.Density = new Density(300, 300);

using (var images = new MagickImageCollection())
{
    // Add all the pages of the pdf file to the collection
    images.Read("Snakeware.pdf", settings);

    var page = 1;
    foreach (var image in images)
    {
        // Write page to file that contains the page number
        image.Write("Snakeware.Page" + page + ".png");
        // Writing to a specific format works the same as for a single image
        var dAngle = image.GetArtifact("deskew:angle");
        image.Format = MagickFormat.Ptif;
        image.Write("Snakeware.Page" + page + ".tif");
        page++;
    }
}

that dAngle value is always null. Is there something that must be done first in order to get the actual angle you need to use to deskew an image?

In addition: if I try to just deskew an image using something like 40%, I get the following exception:

ImageMagick.MagickCoderErrorException: 'TIFF: negative image positions unsupported ./sample/output/noocr1-deskewed.tif @ error/tiff.c/WriteTIFFImage/3972'

[dlemstra]

You deskew an image you will need to use the image.Deskew method. And if you still need the angle it will be returned from that method.

You probably need to call image.RePage after Deskew to make it possible to save the file in the Tiff format.