Changes To The Pixel Timing And Output With Aoi - Basler A202K Manual

Operation and Features

3.7.3 Changes to the Pixel Timing and Output with AOI

When the AOI feature is being used, frame valid will rise at the normal time, however, there will
be a delay between the rise of frame valid and the rise of the first line valid while the camera
discards data from the lines below the AOI. The length of the delay depends on the number of
lines below the AOI.
When the camera reaches the first line in the AOI the camera will begin to output pixel data, but
the line valid bit will remain low indicating that the pixels are not valid. On the pixel clock cycle
where the starting column in the AOI is reached, the line valid bit will become high. The line valid
bit will remain high as the pixels within the AOI are transmitted indicating that these are valid
pixels. Once the pixels within the AOI have been transmitted, the line valid bit will become low.
The camera will continue to transmit the remaining pixels in the line, but as indicated by the low
line valid bit, these pixels are not valid. Any invalid pixels at the beginning and the end of each line
are transmitted as dark pixels (gray value = 0).
After all of the lines in the AOI have been transmitted, the line valid bit will remain low. The fall of
the frame valid bit will be delayed as the lines located above the AOI are discarded. The length of
the delay depends on the number of lines above the AOI. Once the lines are discarded, the frame
valid bit will become low indicating that frame transmission is complete.
To better understand the timing and output changes that occur when using AOI, refer to Figure 3-
13. This timing chart shows what would happen if the AOI was set up with a starting column of
201, a width in columns of 600, a starting line of 101 and a height in lines of 800. As you can see,
there is a delay after the rise of frame valid while the camera discards the data for lines 1 through
100. When the camera reaches line 101, pixels 1 through 200 are output as dark pixels and the
LVAL bit stays low indicating that these pixels are not valid. On pixels 201 through 800, LVAL is
high indicating that the data for these pixels is valid. For pixels 801 through 1004, the camera
outputs dark pixels and LVAL is low indicating that these pixels are not valid. This pattern repeats
as the camera outputs pixel data for lines 102 through 900. After line 900 has been transmitted,
there is a delay while the camera discards lines 901 through 1004 and during this time, the FVAL
bit remains high. Once these lines are discarded, the FVAL bit becomes low indicating that frame
transfer is complete.
If you use a frame grabber that does not take the fall of the line valid bit into account,
you must set the frame grabber for the number of horizontal pixels in the area of
interest. For example, if your area of interest is 600 columns wide, you must set the
grabber for a 600 pixel image width.
If you use a frame grabber that does not take the fall of the frame valid bit into ac-
count, you must set the frame grabber for the number of vertical pixels in the area
of interest. For example, if your area of interest is 800 lines high, you must set the
grabber for an 800 pixel image height.
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BASLER A202