Crop images in C# .NET

To crop images, use the following methods:

Cropping an image

To crop an image, use the Crop method. The input parameters are the following:

  • The coordinates of the top-left corner of the cropped area.
  • The width of the cropped area.
  • The height of the cropped area.

The origin of the coordinate system is the top-left corner of the original image.

To crop an image by 5 percent on all sides, use the following example:

using GdPictureImaging gdpictureImaging = new GdPictureImaging();
int imageID = gdpictureImaging.CreateGdPictureImageFromFile(@"C:\temp\source.jpg");
int height = gdpictureImaging.GetHeight(imageID);
int width = gdpictureImaging.GetWidth(imageID);
// Crop the image by 5 percent on all sides.
gdpictureImaging.Crop(imageID, width * 5 / 100, height * 5 / 100, width * 90 / 100, height * 90 / 100);
gdpictureImaging.SaveAsPNG(imageID, @"C:\temp\output.png");
gdpictureImaging.ReleaseGdPictureImage(imageID);
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Cropping individual sides

To crop an image from an individual side, use the following methods:

Use the Lines parameter to specify how many pixels to crop.

To crop an image from the bottom by 5 percent, use the following code:

using GdPictureImaging gdpictureImaging = new GdPictureImaging();
int imageID = gdpictureImaging.CreateGdPictureImageFromFile(@"C:\temp\source.jpg");
int height = gdpictureImaging.GetHeight(imageID);
// Crop the image by 5 percent from the bottom.
gdpictureImaging.CropBottom(imageID, height * 5 / 100);
gdpictureImaging.SaveAsPNG(imageID, @"C:\temp\output.png");
gdpictureImaging.ReleaseGdPictureImage(imageID);
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Cropping an image background

The CropBorders method detects and removes the background of an image of any color. It accepts the following parameters:

  • ImigingContext sets the image type.
  • Optional: Confidence sets the confidence level for deleting a single line of a background.
  • Optional: ReferencePoint sets the color reference for determining the dominant background color.

To delete the background of an image, use the following code:

using GdPictureImaging gdpictureImaging = new GdPictureImaging();
int imageID = gdpictureImaging.CreateGdPictureImageFromFile(@"C:\temp\source.jpg");
// Detect and remove the background of a photo image.
gdpictureImaging.CropBorders(imageID, ImagingContext.ContextPhoto);
gdpictureImaging.SaveAsPNG(imageID, @"C:\temp\output.png");
gdpictureImaging.ReleaseGdPictureImage(imageID);
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Getting crop area dimensions

To get the dimensions of the cropped area, use the CropBorders method and the following reference parameters:

  • Left is the X coordinate of the top-left corner.
  • Top is the Y coordinate of the top-left corner.
  • Width is the width of the cropped area.
  • Height is the height of the cropped area.

The origin of the coordinate system is the top-left corner of the original image.

If you reference the listed parameters, the CropBorders method only detects the crop area and calculates the cropped area. It doesn’t delete the background. The CropBorders method accepts the following parameters:

  • Confidence sets the confidence level for deleting a single line of a background.
  • ReferencePoint sets the color reference for determining the dominant background color.
  • Optional: ImigingContext sets the image type.

To get the dimensions of the cropped area, use the following code:

using GdPictureImaging gdpictureImaging = new GdPictureImaging();
int imageID = gdpictureImaging.CreateGdPictureImageFromFile(@"C:\temp\source.jpg");
int left = 0, top = 0, width = 0, height = 0;
// Detect the crop area with 50 percent confidence level.
gdpictureImaging.CropBorders(imageID, 50, ReferencePoint.ReferencePointBottomRight,
    ref left, ref top, ref width, ref height);
Console.WriteLine(left + ", " + top + ", " + width + ", " + height);
gdpictureImaging.ReleaseGdPictureImage(imageID);
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Cropping a white background

The CropWhiteBorders method detects and removes the white background of an image. It accepts the following parameters:

  • Confidence sets the confidence level for deleting a single line of a background.
  • SkipLinesCount specifies how many lines to skip.

To delete the white background of an image, use the following code:

using GdPictureImaging gdpictureImaging = new GdPictureImaging();
int imageID = gdpictureImaging.CreateGdPictureImageFromFile(@"C:\temp\source.jpg");
// Detect and remove the white background.
gdpictureImaging.CropWhiteBorders(imageID);
gdpictureImaging.SaveAsPNG(imageID, @"C:\temp\output.png");
gdpictureImaging.ReleaseGdPictureImage(imageID);
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Cropping a black background

The CropBlackBorders method detects and removes the black background of an image. It accepts the following parameters:

  • Confidence sets the confidence level for deleting a single line of a background.
  • SkipLinesCount specifies how many lines to skip.

To delete the black background of an image, use the following code:

using GdPictureImaging gdpictureImaging = new GdPictureImaging();
int imageID = gdpictureImaging.CreateGdPictureImageFromFile(@"C:\temp\source.jpg");
// Detect and remove the black background.
gdpictureImaging.CropBlackBorders(imageID);
gdpictureImaging.SaveAsPNG(imageID, @"C:\temp\output.png");
gdpictureImaging.ReleaseGdPictureImage(imageID);
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Changing a black background color

To change the black background color to white, use the CropBlackBordersEx method. It doesn’t remove the background, which means that the dimensions of the image are kept. This method uses two optional parameters:

  • Confidence sets the confidence level for deleting a single line of a background.
  • SkipLinesCount specifies how many lines to skip.

This method only detects rectangular backgrounds. For irregular shapes, use the DeleteBlackBorders method.

To change the black background of an image to white, use the following code:

using GdPictureImaging gdpictureImaging = new GdPictureImaging();
int imageID = gdpictureImaging.CreateGdPictureImageFromFile(@"C:\temp\source.jpg");
// Detect and change the background color to white.
gdpictureImaging.CropBlackBordersEx(imageID);
gdpictureImaging.SaveAsPNG(imageID, @"C:\temp\output.png");
gdpictureImaging.ReleaseGdPictureImage(imageID);
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Changing a black background color for irregular shapes

The DeleteBlackBorders method is used for images with an irregular black background. The Margin parameter works as a safety buffer, and it sets the maximum distance in pixels from the edges of the image where a border is allowed to start. The default value is 10. Set the SkewedBorders parameter to true to handle irregular shapes.

To delete a black background with an irregular shape, use the following code:

using GdPictureImaging gdpictureImaging = new GdPictureImaging();
int imageID = gdpictureImaging.CreateGdPictureImageFromFile(@"C:\temp\source.jpg");
// Replace the black background from a skewed image by replacing it with white content.
// The maximum distance from edges of an image where a border is allowed to start is 20 pixels.
gdpictureImaging.DeleteBlackBorders(imageID, Margin:20, SkewedBorders:true);
gdpictureImaging.SaveAsPNG(imageID, @"C:\temp\output.png");
gdpictureImaging.ReleaseGdPictureImage(imageID);
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Confidence level

Use the Confidence parameter to set the confidence level of the following methods:

If the line exceeds the specified confidence level, it’s removed or modified. Otherwise, it’s left untouched. The Confidence parameter ranges between 0 and 100 percent. The default value is 75.

To lower the confidence level of the CropBlackBorders method to 50 percent, use the following code:

using GdPictureImaging gdpictureImaging = new GdPictureImaging();
int imageID = gdpictureImaging.CreateGdPictureImageFromFile(@"C:\temp\source.jpg");
// Detect and remove the background with 50 percent confidence level.
gdpictureImaging.CropBlackBorders(imageID, 50);
gdpictureImaging.SaveAsPNG(imageID, @"C:\temp\output.png");
gdpictureImaging.ReleaseGdPictureImage(imageID);
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Skipping lines

Use the SkipLinesCount parameter to specify how many lines to skip when using one of the following methods:

To use this parameter, specify the Confidence parameter:

using GdPictureImaging gdpictureImaging = new GdPictureImaging();
int imageID = gdpictureImaging.CreateGdPictureImageFromFile(@"C:\temp\source.jpg");
// Detect and remove the background with 75 percent confidence level and skip 3 lines.
gdpictureImaging.CropBlackBorders(imageID, Confidence:75, SkipLinesCount:3);
gdpictureImaging.SaveAsPNG(imageID, @"C:\temp\output.png");
gdpictureImaging.ReleaseGdPictureImage(imageID);
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Reference point

Use the ReferencePoint parameter to specify the dominant color of the background of the image. The possible values are the following:

  • ReferencePointBottomLeft
  • ReferencePointBottomRight
  • ReferencePointTopLeft
  • ReferencePointTopRight

The following functionalities can use this parameter:

Imaging context

Use the ImigingContext parameter to specify the image type. The possible values are the following:

  • ContextDocument
  • ContextPhoto
  • ContextUnknown

The following methods can use this parameter: