1.Why is flat-field correction (PRNUC) necessary for linear-array cameras?

The need for flat-field correction (PRNUC) in line-scan cameras primarily stems from anomalies in the acquired images, such as inconsistencies between the brightness at the image edges and the brightness at the center. These anomalies can significantly affect the quality of image data obtained using cameras in field applications. Therefore, flat-field correction is necessary for line-scan cameras under the following circumstances:

(1)Uneven lighting

(2)The response at the center of the lens differs from that at the edge of the lens.

(3)The response of each pixel in the imaging device is inconsistent.

(4)Fixed image background noise

Under normal circumstances, the abnormal image is shown as follows:

2.Steps for Flat-Field Correction (PRNUC)

2.1Confirm before flat-field correction (PRNUC)

(1)The field of view should consist of a flat, crease-free white sheet of paper that completely fills the camera’s entire field of view.

(2)The grayscale values of the camera image must be maintained between 120 and 160, and the difference between the grayscale value of the brightest pixel and that of the darkest pixel must not exceed four times. (To view the grayscale values of individual pixels, you can move the mouse over a specific pixel in the image.),In the mil software, you can stop the stream to view the R, G, and B channel values. In MVS, you can view the R, G, and B channel values without stopping the stream, as shown below:

(3) The images captured by the camera need to be blurred as much as possible (blurring the entire image to minimize the impact of white paper on flat-field correction).

Focus the lens to create a shallow depth of field, after which the entire image becomes blurred.

Using the low-pass filtering function in PRNUC, once this function is enabled, the image becomes noticeably blurrier, producing an effect similar to that of a defocused lens.

2.2Flat-Field Correction (PRNUC) Procedure

After setting up the above configurations and taking note of the relevant precautions, proceed with flat-field correction (PRNUC). At this stage, the operation requires only adjusting the camera-side parameters operation;

(1) Shading Selector: Select PRNUC Correction (as indicated by number 1 in the figure)

(2) Activate Shading, then click Execute (wait 2-3 seconds after Step 2 before proceeding to Step 3) (as indicated by number 2 in the figure).

(3) Check the PRNUCEnable box to enable (as indicated by number 3 in the figure).

The comparison of images before and after correction is as follows: