Take the 2-minute tour ×
Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It's 100% free, no registration required.

I have an Normalized Difference Vegetation Index(NDVI) and Enhanced vegetation index (EVI) layer and I want to re-scale their data ranges to value ranges from 0–to–1, in order to optimally stretch the contrast (information contained in the image). I have analysed the histogram of the distribution of grey values and need to omit the lowest 0.5% and the highest 0.5% of the data, however I am not too sure how to go about doing this. I tried doing this in excel (manually deleting 0.5% min and 0.5% max values) and then completing the step in ERDAS model builder. The formula used in model builder (NDVI- new min)/(new max-new min), however my results were unsuccessful.

share|improve this question
    
This may be of interest: hexagongeospatial.com/Community/forums/t/870.aspx –  Aaron Jul 21 at 13:51

1 Answer 1

Rescaling an NDVI or EVI from -1 to 1, to 0 to 1, uses the Rescale function (under Raster, Radiometric).

enter image description here

Clipping the top and bottom 0.5% is a percentage linear contrast stretch. To do this in ERDAS 2013, click on Panchromatic, then General Contrast. This brings up the Contrast Adjust window (seen below), and you can choose a variety of different methods of contrast adjustment.

You want to use Percentage LUT and set the % accordingly.

Contrast Adjust Dialog Screenshot

(I'm not sure of the specific steps in other versions unfortunately.)

share|improve this answer
    
Thank you for your respose, however Percentage LUT only changes the lookup table, the actual digital values do not change, and I am after finding a new minimum and maximum value (essentially by getting rid of 5% of the min values and 5% of the max values) –  Mokhine Motswaledi Jul 23 at 14:28
    
In that case, Rescale twice: once with "Clip to this range?" checked (to trim the tails, using desired min/max of your current range), then again to rescale to a 0-1 range. –  Erica Jul 23 at 14:37

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.