Where does AdaptiveThresholdFilter live in the IronBarcode API?

AdaptiveThresholdFilter is a class in the IronBarCode namespace, shipped in IronBarCode.dll. It derives from Object and implements IImageFilter, so it can be added to the ImageFilterCollection assigned to BarcodeReaderOptions.ImageFilters.

When should you use AdaptiveThresholdFilter instead of BinaryThresholdFilter?

Use AdaptiveThresholdFilter when lighting across the image is uneven, since it computes a separate threshold for each region. Use BinaryThresholdFilter when a single global cutoff is enough, such as a uniformly lit image.

How do you apply AdaptiveThresholdFilter before reading a barcode in C#?

Create an ImageFilterCollection containing a new AdaptiveThresholdFilter, assign it to BarcodeReaderOptions.ImageFilters, and pass the options to BarcodeReader.Read with your image. The filter runs in collection order before decoding.

Class AdaptiveThresholdFilter

A filter to apply adaptive thresholding to an image.

Inheritance

System.Object

AdaptiveThresholdFilter

Implements

IImageFilter

Namespace: IronBarCode

Assembly: IronBarCode.dll

Syntax

public class AdaptiveThresholdFilter : Object, IImageFilter

When a barcode image has uneven lighting, glare, or a shadow falling across part of the frame, a single global cutoff cannot cleanly separate the bars from the background, and AdaptiveThresholdFilter is the preprocessing step that handles it. It applies a Bradley adaptive threshold, computing a local cutoff for each region of the image rather than one value for the whole picture, so a barcode that is bright on one side and dim on the other still binarizes into clean black bars on a white field. This is the filter to reach for on photos and scans with non-uniform illumination, where a plain binary threshold would lose part of the code.

The filter is one of the IImageFilter implementations that go into the ImageFilterCollection assigned to BarcodeReaderOptions.ImageFilters. The reader applies the filters in collection order before it attempts decoding, so an adaptive threshold typically sits early in the pipeline, ahead of a sharpen or contrast pass, because it produces the clean two-tone image those later steps refine. A developer constructs the filter, adds it to the collection, and passes the options to BarcodeReader.Read along with the source image.

Several constructors trade off convenience against control. The parameterless form uses tuned defaults, while overloads accept a Threshold, the Lower and Upper replacement colors, and a Rectangle that confines the operation to a region of interest. The Threshold property sets the sensitivity of the local comparison, Lower and Upper choose the two output colors the pixels collapse to, and Rectangle restricts the filter to part of the frame when only one zone needs correcting. Tune Threshold first; the defaults already suit most documents with patchy lighting.

using IronBarCode;

var options = new BarcodeReaderOptions
{
    ImageFilters = new ImageFilterCollection { new AdaptiveThresholdFilter() }
};
var results = BarcodeReader.Read("uneven-lighting.png", options);

The image correction how-to walks through each filter on a sample barcode, and the imperfect barcode example shows a full read of a low-quality image. For images that are also skewed or rotated, the image orientation correction how-to is the companion guide.