<div class="gmail_quote">On Thu, May 31, 2012 at 4:08 PM, David Doria <span dir="ltr"><<a href="mailto:daviddoria@gmail.com" target="_blank">daviddoria@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
I am trying to look for the pixels in an image whose magnitude are<br>
above a certain value. I loaded the image, then tried to use the<br>
Threshold filter. The tooltip says "Requires an attribute array with 1<br>
component."<br>
<br>
Question 1) Would it make sense to allow this filter to operate on one<br>
of the channels of the image instead of having to extract it manually?<br>
<br>
To generate this attribute array, I used the Calculator filter to make<br>
an array called AbsX with abs(MetaImage_X). Then I applied a Threshold<br>
filter to this new array. The values in this array are in [0 512].<br>
When I leave the Lower Threshold all the way down and the Upper<br>
Threshold all the way up, I can view the image just fine. In the<br>
Display tab, the Color By is set to AbsX, like I want. However, as<br>
soon as I move the Lower Threshold slider, the image disappears. When<br>
I look in the Display tab, the only option for Color By is now Solid<br>
Color.<br>
<br>
Question 2) Why would the Color By options change based on the<br>
threshold that is set? (I'd also ask why the image is disappearing,<br>
but I think it might have to do with the coloring).<br>
<br>
If I then try to glyph the output of the threshold filter (to draw<br>
spheres or something at the location of the pixels that remain), the<br>
Scalars option of the glyphs shows my AbsX array, but it is not<br>
enabled. The only choice is under Vectors, and it is my MetaImage<br>
array.<br>
<br>
Question 3) Why can I not glyph the AbsX array?<br>
<br>
Sorry for the long winded question, but hopefully someone can shed<br>
some light on these issues!<br>
<br>
Thanks,<br>
<br>
David<br>
</blockquote></div><br><div>Any thoughts on this? Is it just impossible, or am I missing something?<br clear="all"><br>David<br></div>