Good evening,
If I use 95% or 100% how can I define the changes in my image?
And before the use of 95% and 100% how can I define my image?
Thanks in advance again. This forum is really important for me.
the percentage just defines how your greyscale is distributed over the image. 100% includes the absolut lowest (black) and highest (white) values while 95% leaves out 2.5 at the top and bottom to exclude outliers. This usually delivers better contrasts for viewing the image. But none of these options changes your pixel values.
If you want to compare images of different dates, you will have to calibrate them first.
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Thanks again.
Now I have one doubt, if I don’t use 100% or 95% then how is distributed greyscale over the image i.e after terrain correction in my case?
95% is the default.
If you change the left slider you set the lower limit to the corresponding value. The same for the right slider and the upper value.
The value range in between is mapped to the 255 gray scale value.
Honestly, we are happy that you use SNAP and want to keep you as a user but this is a forum for the usage of SNAP and not one for learning the basics of image processing and remote sensing. I think there are better resources for this. Maybe you think about buying a good book about image processing and remote sensing.
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Forgive me for my questions, I’m really sorry, I don’t wish to disturb anyone.
My doubts are born because I have read this in SNAP manual:
A click on the icon adjusts the sliders to cover 95% of all pixels in the band.
A click on the icon adjusts the sliders to cover 100% (the full range) of all pixels in the band.
But I have initially a image with contrast that is different from what I get with 95% and 100%, so 95% isn’t the default in my opinion.
I think the question is what is the “default” stretch as it is neither 95% nor 100%…
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Now I got your question.
By default the lower 1% percent are cut and the upper 4%. When clicking on 95% the lower and the upper 2.5% are cut.
So both cases are 95%, but with different cuts.
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I have another important doubt .
Please, this my affermation about 95% is correct?
“When I click on 95% the real pixel values lower and the upper 2.5% are cut, that is the real pixel values lower 2,5% are mapped to 0 gray scale value while the real pixel values upper 2.5% are mapped to 255 gray scale value”
Thanks again.
Yes, you are right. All values in the lower 2,5% range are mapped to black (0) and all pixels above 97,5% to white (255).
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