I think I understand what your'e asking better now...
If you separate the interlaced image the way I described before (using
the CWIMAQVision.InterlaceSeparate) into two separate image buffers,
you'll see the Odd/Even fields come out separately, where one set of
fields clearly shows no dot and does have the 298 in the time, while
the other shows the center dot and has a 315.
The effect you're seeing upon zooming is related to what particular
algorithm the CWIMAQViewer uses to resample the image for display.
Obviously, the image will look fine at 1x zoom, but when you tell it to
zoom to 0.5x, it has to choose what pixels to display and how it wants
to approximates the resized display. In this case, zooming out to 0.5X
means cutting the each dimension in half, to where two adjacent pixels
are now displayed as one single pixel; this is calculated for both the
horizontal and vertical dimensions. Different algorithms exist for
doing this - do you choose the top-most or left-most pixel each time
you have to resize down? Do you average the two pixels together to make
a single output pixel? Do you take a weighted average of even more
pixels around them to make the transition to the next pixel smoother?
Similarly, scaling an image up (or zooming in on it) might also use
different interpolation methods to "fill in" the new pixels you create
by expanding your image. Terms such as zero-order/nearest neighbor
interpolation and bicubic interpolation are explained in good detail on
the following
third-party page.
Oftentimes, the rougher methods of interpolation are used in order to
reduce processing time and provide more responsive or smoother zooming.
Since you are not actually changing the image itself when zooming, most
graphics packages use the rougher methods without worrying about losing
picture information.
Each software program can have a different way of handling this. If you
load the TIFF file into any of the following picture viewers - Windows
Picture & Fax Viewer (the default program in WinXP for previewing
images), Photoshop, Irfanview, or GIMP, they may all give slightly
different results when zoomed in or out. Similarly, if you actually
perform resampling to resize the image down in any of those programs,
you may get slightly different results. In LabVIEW's case, it appears
to be tossing out every other field and just displaying the odd field
lines (and I assume tossing out every other column too), resulting in
an image which looks a lot like when you separate out just the odd
fields.
***
Edit: To answer your question on regions of interest specified on the viewer panel, you can use the CWIMAQViewer.Regions property to view this. Also check out the CWIMAQRegions data type. See the NI Vision for Visual Basic help in Start » Programs » National Instruments » Vision » Documentation » NI Vision (it is not located in the NI-IMAQ documentation directory). for more info. The description for CWIMAQRegions is as follows:
CWIMAQRegions
CWIMAQRegions is a collection of CWIMAQRegion objects. Every CWIMAQViewer control has a CWIMAQRegions collection associated with it, which you can use to add and manipulate region objects on the viewer. In addition, you can create a CWIMAQRegions object that is not associated with a CWIMAQViewer control.
Message Edited by VGA CD-ROM on
05-27-2008 11:40 PM
