| Re: Changing values of one image from ENVI [message #62317 is a reply to message #62241] |
Sun, 31 August 2008 08:30  |
devin.white
Messages: 50
Registered: March 2007
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Member |
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On Aug 29, 8:15 pm, Jonathan Greenberg <jgrn...@gmail.com> wrote:
> Txomin:
>
> I need to write a thread at some point extolling how much I hate
> "ENVI_GET_DATA" -- its one of the most useless commands in the ENVI
> language. I am a HUGE fan of ENVI_GET_SLICE and, if you want to get
> more complicated, use the built-in envi tiling routines (which are
> really just envi_get_slice x a number of lines dependent on memory).
> The idea is, you read one line at a time, process it, write the output
> one line at a time... No memory issues, fast read/write, all good.
>
> --j
>
> On Aug 29, 8:20 am, txominher...@gmail.com wrote:
>
>
>
>> Hello,
>> I would like to change some pixel values of one image loaded with
>> ENVI_OPEN_FILE, but I cannot load the entire image in memory (this is
>> a very big image).
>> What I do is to access and process some specific regions of the image
>> using ENVI_GET_DATA, by defining subsets in DIMS.
>> I really wonder if there is any keyword in the procedure
>> ENVI_WRITE_ENVI_FILE, or other procedure (something inverse to
>> ENVI_GET_DATA) to perform this, because the only choice that I know is
>> to load the whole image in memory in IDL and write it again.
>
>> Thanks
>
>> Txomin- Hide quoted text -
>
> - Show quoted text -
ENVI_GET_DATA, ENVI_GET_SLICE, and the ENVI tiling mechanism represent
three different ways to access image data. I sometimes will use all
three in the same program--depending on what kind of processing I need
to do. They each have their strengths and weaknesses. For example,
if I was interested in multi-scale spatial processing (not spectral),
ENVI_GET_SLICE would be pretty useless since I can only retrieve one
line at a time at full spatal resolution and the data is ordered in
BIL or BIP. ENVI_GET_DATA is perfect for that task. The tiling
mechanism is very flexible and can go either way, but requires more
programming overhead and is often overkill for the task at hand.
However, there are times when it is the best option. I wouldn't
recommend it for this task, though.
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