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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.

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This may be of interest: – Aaron Jul 21 '14 at 13:51

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.)

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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 '14 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 '14 at 14:37

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