Image scaling produces moire

[chrbesold]

I use Labview 8.01 and need to read grayscale images (bmp, png) and fit them to user window for display.

Images are scaled via entering a scaling factor into property node for the frontpanel display. If the scaling factor is larger or equal to one, everything is fine. But when I use a factor smaller than 1, the image size is correctly changed, but the smaller image contains e.g. black lines where only smooth gray fields are in the original image. Maybe that is due to a bad scaling algorithm, but of course I cannot change it.

Any idea to solve this problem?

Attached are screenshots of the problem, a VI to quickly test it and an example image file.

[chrisger]

hi there,

have you tried the Image Controls from the Vision - palette? they won't show any moire effects. maybe you have to install image acquisition from your device drivers CDs first,

[zou]

I believe this problem has been posted here before.

You can use Image Toolbox (http://www.geocities.com/gzou999/imgtool.htm) to solve this problem.

[chrbesold]

I'm sorry, but the image toolbox you posted doesn't work on my labview. It can't read the sub-VIs, telling me that they have no block diagram. Never seen this error before....

And I do not have the Vision-package - just no license available at my department.

Any other ideas?

[chrisger]

hi there

as far as i remember there's a vision subset for image aqcuisition, file handling and display on the LabVIEW instrument drivers CDs, but this is not installed by default. this subset is sufficient for displaying images using the image control from the "Vision" palette.

[zou]

What version of LabVIEW are you using?

Image Toolbox doesn't use Vision package.

[chrbesold]

As already mentioned, I use Labview 8.01, but do not have the vision package.

Image toolbox demo is only available up to LV 7.1.

Additionally, I officially am not allowed to use third-party software for this project.

Seems to be overclassed anyway for my problem.

So I'm just interested in another image scaling algorithm, which should not have any interpolation capabilities to enlarge a picture, but be able to shrink it for display - without any change to grayscale values.

Message Edited by chrbesold on 07-26-2006 09:11 AM

[chrisger]

hi there

the attached 7.1 vi uses the image control and basic image vis included in the device driver cds of LabVIEW. as i mentioned in an earlier post you don't need the vision module to use these basic file read and display functions. maybe you have to install the image aqcuisitiuon vis from your device drivers cd first.

[chrbesold]

@chrisger:

When opening your file, Labview does not find a file called IMAQ ReadFile. If I ignore it, the VI opens without this file. I have installed the IMAQ package... see attached screenshot.

There I discovered another problem with your file: It only allows integer values for scaling, but not the critical range between zero and one.

I tried one VI supplied by NI to which I just have added the image selector, and even this file shows the same behaviour as my own one does. I also attached this version.

Message Edited by chrbesold on 07-26-2006 10:00 AM