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On a DMA transfer the width of each individual line is discarded. Only the frame data will be stored in the PC memory. By using FG_TRANSFER_LEN the number of byte of the transfer can be obtained. Any line length information is discarded.
So information about the image dimensions have to be appended as a trailer to the image.
In the post Extact ROIs from linescan images using a Blob Analysis images of different sizes are cropped using ImageBufferMultiRoIDyn operator. I think in this thread most of your question is answered.
Instead of the presented solution above you can measure the current image width and height just before the DMA transfer.
See the attached VA design.
In microDisplay variable image dimensions cannot be displayed. Because microDisplay is a test only tool you could increase the size of each image with SyncToMax and SyncToMin to have a constant image size. However this is only for testing as it will require more DMA bandwidth:
Let me know if you have further questions.