Application of distortion correction on endoscopic laryngeal images

Introduction:

Due to the nature of the optics used in endoscopes and cameras, a typical degradation in endoscopic images – barrel-type distortion or wide-angle (fish-eye), is observed. This inhomogeneous magnification interferes with diagnosis as it distorts the shape of the visualized objects and changes in non-linear manner the different parts of the field.

Methods:

In 23 patients (age 4 months – 5 years;14 male, 9 female) endoscopic image of the larynx was recorded during standard intubation for other surgical indications. Uniform equipment was used: 70o 4 mm rigid endoscope and an endoscopic camera with digital recorder system. The variable factors were the optical zoom and focus of the camera. After each patient the photo-optical system was mounted on a stand to take a picture of a calibrated raster. Further the images were processed in GIMP (GNU Image Manipulation Program v.2.8.). The filter Lens Distortionr was used to produce a corrected image of the raster with straightened lines. The same settings of the filter were applied to the endoscopic image of the same pair. Raw and corrected images were analyzed.

Results:

The level of correction of the images with the Lens Distortion filter of the image editing software varied significantly from -36,767 to -78,498. With the calibration of the pictures real proportional image of different anatomical variations of the larynx was obtained.

Conclusion:

Endoscopic images (and particularly of the larynx) appear to be significantly affected by the natural distortion, attributed to the rigid endoscope used. Post-procedural calibration algorithm based on a calibrated raster is proposed. Such distortion correction method could be clinically useful in the context of endoscopic evaluation of the laryngeal anatomy and pathology.

Publication History

Publication Date:
18 April 2018 (online)