Posted by
Michael Schmid on
Jan 03, 2011; 10:03am
URL: http://imagej.273.s1.nabble.com/Tracking-Image-Changes-with-IMAGEJ-tp3685182p3685188.html
Hi Catherine,
it looks problematic - the elevation of the sun was different in the
two images, and this may lead to an apparent shift of the dunes
(unless the crests are sharp enough so that the sunlight-shadow
border is independent of sun elevation).
Roughly, you could try the following steps:
- Align the images such that a known stable feature is at the same
pixel position in both (e.g., measure the position of that feature
with the cursor, translate one of the images until it matches.)
The Sync Windows plugin from the ImageJ website may help.
- Identify the crests (e.g. Process>Filters>Convolve with a kernel
like "-1 0 1" or reverse for crests running in y direction), and try
various filters to make them stand out clearly, suppressing all other
signal as much as possible.
- You may then see how much you have to shift the images to make the
dunes conincide (e.g. copy, paste with "Subtract" in paste Control,
and nudge with the cursors) or try the bUnwarpJ plugin on the two
images to get the shift.
Michael
________________________________________________________________
On 2 Jan 2011, at 22:40, ImageJ Lover wrote:
> Hi! I asked a question about tracking image changes a while back.
> Thanks for
> all the help! I was wondering if anyone could give me more specific
> advice
> if I attached the actual images I was using. All my images are
> grayscale.
> They all come off of the HIRISE imaging database, which takes high
> resolution images of the Martian surface. The dunes are pretty clearly
> delineated via their raised ridges. The files are too large to
> attach, but
> I've included the links to two images I’m analyzing from the HIRISE
> database. I'm working with the images entitled "full image
> (grayscale, map
> projected)" found in the link on the right hand side of the page. Both
> images have a scale of 50 cm/pixel. In the bottom right corner of each
> image, inside the impact crater, there's a raised sand mound that I
> know
> hasn't moved. Specifically, I'm trying to measure how many meters
> the sand
> dunes above that impact crater have moved from one image to the
> next. It
> doesn't need to be perfect. I just need a rough estimate. At most,
> I'll
> analyze two or three image sets. I can do as many steps by hand as is
> necessary to achieve a successful result. Thank you so much!
> ~Catherine
>
>
> From November 2007:
>
http://hirise.lpl.arizona.edu/PSP_005931_1080> From July 2009:
>
http://hirise.lpl.arizona.edu/ESP_013829_1080>
>
> On Tue, Dec 14, 2010 at 1:56 PM, Damon Poburko
> <
[hidden email]>wrote:
>
>> Hi Catherine,
>>
>> Sounds like a fun project. We could probably use a little more
>> info on
>> what kinds of features you want to track. Do the dunes stand out
>> clearly
>> from other features? Do they have a common shape? Are you working
>> with color
>> or grayscale images? How do you define "dune" vs "not dune" in the
>> images?
>> It might be helpfull if you could provide some example imags. I'm
>> sure
>> ImageJ is capable of measuring what you want to know. Just be sure to
>> provide a little more detail on what exactly you want to measure.
>> Also, how
>> many images are you planning to ananlyze. Is it few enough that it
>> will be
>> reasonable to do a few steps by hand?
>>
>> Cheers,
>> Damon
>>
>>
>> On 12/14/2010 10:08 AM, Catherine Zucker wrote:
>>
>>> Hi,
>>> I'm a high school senior researching dune migration on Mars. I
>>> need to
>>> measure how many meters the dunes have moved in a certain number
>>> of months.
>>> I've been trying to do this with IMAGEJ, but am finding it
>>> difficult. Does
>>> anyone know a way to track the migration of an entire dune using
>>> IMAGEJ?
>>> Does anyone have experience with tracking image changes? Thanks!
>>>
>>