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How to automatically deskew an image

Generally, there are two ways to automatically deskew an image.

Enable the capability of a scanner

Applicable only to compatible TWAIN scanners

There is a standard TWAIN capability called ICAP_AUTOMATICDESKEW which, when enabled, does the deskewing of all scanned images automatically. If your scanner supports this capability, you can enable the functionality through DWT using the API IfAutomaticDeskew

DWObject.OpenSource();
DWObject.IfAutomaticDeskew = true;

Use DWT to deskew an image as it is scanned

The function deskew() below is applicable to all platforms. The event OnPostTransferAsync is only triggered during scanning

function deskew(index) {
    DWObject.GetSkewAngle(
        index,
        function(angle) {
            console.log("skew angle: " + angle);
            DWObject.Rotate(index, angle, true,
                function() {
                    console.log("Successfully deskewed an image!");
                },
                function(errorCode, errorString) {
                    console.log(errorString);
                }
            );
        },
        function(errorCode, errorString) {
            console.log(errorString);
        }
    );
}
DWObject.RegisterEvent("OnPostTransferAsync", function(info) {
    deskew(DWObject.ImageIDToIndex(info.imageId));
});

How to insert images to a specified index

By default, when you scan or load images, they are appended to the end of the image array in buffer. However, in some business scenarios, the user might want to insert these new images to a specified index. Unfortunately, DWT doesn’t provide a native method for that. The following code snippet shows how it can be done

Insert when acquiring

function acquireToIndex(index) {

    DWObject.IfAppendImage = false;
    DWObject.CurrentImageIndexInBuffer = index;
    DWObject.RegisterEvent('OnPostTransfer', function() {
        DWObject.CurrentImageIndexInBuffer++;
    });
    DWObject.RegisterEvent('OnPostAllTransfers', function() {
        DWObject.IfAppendImage = true;
    });
    DWObject.AcquireImage();

}

function loadToIndex(index) {

    var oldCount = DWObject.HowManyImagesInBuffer;
    DWObject.RegisterEvent('OnPostLoad', function() {
        var newCount = DWObject.HowManyImagesInBuffer;
        for (var j = 0; j < newCount - oldCount; j++)
            DWObject.MoveImage(oldCount + j, index + j);
    });
    DWObject.LoadImageEx('', 5);

}