How We Test for Defective Pixels

Overview

The suite of quality assurance tests that Teledyne performs on its cameras includes specifications for identifying and correcting defective pixels - also called white blemish pixel defects - that originate from the camera imager. Defective pixels can occur randomly in any imager and are believed to be caused by natural cosmic radiation. In some cases, an incidence of radiation can damage a pixel and cause it to generate a permanently high charge. As a result, the pixel takes on a permanently lit, or ‘glowing,’ appearance. This damage generally occurs after the sensor is manufactured, particularly during shipping and handling. Defective pixels are sometimes referred to as ‘hot,’ ‘burned’ or ‘bright’ pixels.

In the following image, a single defective pixel may be seen near the lower right corner (circled).

The pixel is magnified in the following image:

Correcting Defective Pixels

Testing and correcting defective pixels occurs during the unit test phase of camera production. This means that an array of blemish pixels is identified for each individual camera, and the mechanism to correct them is then coded into the camera firmware. Pixel correction, as such, becomes a part of the on-camera data flow for every image frame. The algorithm to correct blemish pixels involves applying the average color or grayscale values of neighboring pixels to the blemish pixel.

Test Specifications

The following specifications apply to all cameras when testing for defective pixels:

• All tolerances meet or exceed those of the corresponding imager manufacturers.
• The temperature setting is 23 C.
• Tests are performed with the lens cap on (darkness).
• White balance, where supported in color models, is applied according to the default setting of the camera on startup.
• Blemish pixels identified on the outermost columns (left/right) of pixels in the image are not corrected.

Note that the maximum number of pixels corrected varies by camera model, depending on storage space and sensor size. While we aim to ship cameras with zero defective pixels, in some models the maximum number of pixels corrected may be less than the number allowed by the sensor manufacturer.

Determining Pixel Correction on Your Camera

To determine if pixel correction is enabled on your camera (the default setting is enabled), and the number of pixels that are being corrected, check the Defective Pixel Correction Control (GenICam cameras) or read the PIXEL_DEFECT_CTRL register 0x1A60h (IIDC cameras). 

Minimizing the Effects of Defective Pixels

You may still encounter issues with defective pixels, in spite of any correction that is performed on-camera. Keep in mind that blemish pixels can occur spontaneously after they leave Teledyne, especially during shipping and handling.

To minimize the effects, be aware that higher operating temperatures, higher gain settings, and longer shutter times can all contribute to an increased effect of defective pixels.

If you remain concerned about pixel defects on your camera, contact our support team.