| ENVI: how to avoid stretching in image displays? [message #40352] |
Mon, 09 August 2004 12:03  |
wl2776
Messages: 13
Registered: February 2004
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Junior Member |
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Hi all.
I have an image in byte binary format with pixel values ranging from 0
to 104.
And I have a color table specifying colors for each of those 105
values.
These colors are situated in the table in places with numbers 0-104.
So, it is supposed, that displayed pixels will have colors, which
numbers equal pixel values.
However, when I try to display image it is displayed with stretch
(linear or gaussian or else) and pixels are assigned with another
colors, whith numbers differing from the pixel values.
How to avoid the stretching?
In other words, how to make ENVI to display pixel, having value 0,
with color number 0 from the color table, to display pixel, having
value 1, with color number 1 from the color table, etc?
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| Re: ENVI: how to avoid stretching in image displays? [message #40488 is a reply to message #40352] |
Tue, 10 August 2004 01:25  |
tianyf
Messages: 6
Registered: June 2004
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Junior Member |
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The answer is in the ENVI help documents.
If you want to display just this image with raw DN, select [Quick
Linear 0�255] from <Display Menu> - <Enhance>. Or you can set the
default stretch type in <Preferences> - <Display Default> (% Linear
equals 0 means no enhancement).
Tian.
wl2776@yandex.ru (wl) wrote in message news:<1c9e5a19.0408091103.2598f9e5@posting.google.com>...
> Hi all.
> I have an image in byte binary format with pixel values ranging from 0
> to 104.
> And I have a color table specifying colors for each of those 105
> values.
> These colors are situated in the table in places with numbers 0-104.
> So, it is supposed, that displayed pixels will have colors, which
> numbers equal pixel values.
>
> However, when I try to display image it is displayed with stretch
> (linear or gaussian or else) and pixels are assigned with another
> colors, whith numbers differing from the pixel values.
>
> How to avoid the stretching?
>
> In other words, how to make ENVI to display pixel, having value 0,
> with color number 0 from the color table, to display pixel, having
> value 1, with color number 1 from the color table, etc?
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| Re: ENVI: how to avoid stretching in image displays? [message #40511 is a reply to message #40478] |
Mon, 16 August 2004 08:49 |
adam_e_oconnor
Messages: 2
Registered: August 2003
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Junior Member |
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ENVI's default stretch is 2% Linear, which explains the observed
behavior. You can view this setting by selecting "File > Preferences"
from the main ENVI menu and selecting the "Display Defaults" tab. If
you want to permanently turn off ENVI's automatic stretching you
actually should select "Linear Range" and enter "0" in the minimum box
on the left and "255" in the maximum box on the right. That way byte
values ranging from 0 --> 104 are actually displayed as 0 --> 104.
Simply changing the "% Linear" setting to "0.0" will eliminate the 2%
saturation, but there is still a linear stretch applied such that 0
--> 104 will be displayed as 0 --> 255, which is not what you want in
this case. You can confirm that your data values are being accurately
displayed by using the "Tools > Cursor Location/Value..." utility from
the menu system within any display window. The "Scrn: R: G: B:"
values should match the "Data:" value. Keep in mind that after you
make changes to the Preferences you must re-display any images that
are already open in order for the changes to take effect.
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