Re: clarity of projected enlarged dicom films
- From: eric.goodall@xxxxxxxxx
- Date: 1 Jul 2005 11:02:19 -0700
By "cath films" one presumes you mean xray angiography multiframe
cines. Typically XA videos are 1024x1024 pixel matrices. If you're
displaying on a 19" monitor (diagonal measure) and assume you're
running a 1280x1024 display resolution to get full resolution display,
this implies you're displaying 1024 pixels over linear distance 301 mm
or 11.8 inches. This comes out to about .29 mm per pixel (or 0.0115
inches per pixel) on the flat panel monitor. At that size, your eyes
will smoothly integrate between the pixels and you won't notice the
inherent "blockiness" of the data on the display; but when those some
pixels are 1mm or bigger on the display screen, you do notice it.
Some of the effect that you're seeing is simply due to the integrating
effect of the human retina and the resolution limits of the digital
data you're viewing. When the pixels are small, your eye&brain smooth
out the transitions; but when the pixels get larger than a critical
threshold, your eye will see the pixel transitions, causing it to
appear to lose resolution. You would see some of the same loss of
clarify, if you were to display the same data on very high resolution
flat panel monitor - if you have any 5MP monitors on a radiology PACS
workstation at your hospital, try it displaying your cines on them.
While probably not as bad as the way it looks on the proxima, it still
looks worse than on a smaller monitor. You didn't say how close you
were to the projected image, but sitting further back or reducing the
size of the projected image (by placing the projector closer to the
projection surface) will help some.
Another factor is the loss of contrast. Some of this is the projector
itself. Some more is the poor efficiency of the reflection of the image
from the wall and or screen. There is no way a backlit monitor screen
is going to be as good as the reflection of a projected image. If
you're using a wall, get a screen to project on. You can also
counteract some of the contrast loss acking up the projector
brightness and contrast. You should also try changing the viewing
software window/level settings to increase the digital contrast This
may cause some of the detail that you can see on the flatpanel to be
lost, but you probably wouldn't be able to see those details on the
projected image anyway.
.
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