The default behaviour of DicomObjects is to use smoothing for minimised images, where ActualZoom is < 1 (ensuring that all image pixels contribute to the display), but not to use it for images scaled up (in order to minimise regulatory concerns about “enhanced” images and possible artefacts). See MagnificationMode & MinificationMode for more details.
Whilst this is a preferred settings for most cases, it does have a performance penalty, and if left enabled during fast update operations the display update appears to be slow or “jerky”.
For maximum performance, please ensure that smoothing is entirely disabled, whilst such operations are in progress by setting the image’s MagnificationMode and MinificationMode properties both to Replicate(.NET) and doFilterReplicate(COM). They can be reset to their previous values (according to your preferences) once the operation is complete. As most operations of this sort are accomplished using a mouse (either on a slider control or over the image window), the best way to achieve this is to set the values to Replicate (as shown above) in the MouseDown event and reset to preferred display values in the MouseUp event.