I have an image with value ranging from -1 to +1.

I want to convert this into 0-255 (8bit).

How can this be done using ArcGIS for Desktop or ERDAS IMAGINE?

  • is it floating point? i.e. are values -1, 0 or 1 or decimal values between -1 and 1? Note 8 bit can also be signed 8 bit, just not seen very often (-127 to 128) Sep 18 '14 at 4:33
  • yes I have decimal values also.
    – nilushika
    Sep 18 '14 at 4:36

You will want to stretch your floating point data from (-1 to 1) to (0 - 255). You can accomplish this very easily in Erdas Imagine:

Raster tab > Resolution Group > Radiometric > Rescale

enter image description here

  • That does sound easier Aaron. I reckon that would be the way to do it... almost makes me wish I got around to learning how to use ERDAS. Sep 18 '14 at 5:42
  • In this case, rescaling data is very easy in Erdas--it eliminates a few steps that you describe using ArcGIS. Any type of bulk image processing is almost always more efficient and easier in Erdas. It is definitely worth a look.
    – Aaron
    Sep 18 '14 at 5:47

Using ArcGis Raster Calculator multiply by 127 and then add 128. This will give you a value between 0 and 255 which will be floating point then use Int to convert to an integer and Copy Raster specifying 8 bit unsigned as the output pixel_type.

Another way to do this is to do a nice stretch in ArcMap and then right click on the layer, select data::export data then check the box Use Renderer which will force the data into 8 bit using the colour scheme you have applied (and even optionally RGB).

  • It is @Aaron, but it only works for 8 bit. If you use a colour ramp with real colours then that what you get - a pseudocolour 8 bit image not monochrome. It can be handy to 'freeze' your elevation etc. data into a specific colouration rather than trying to apply the same ramp and stretch on multiple workstations/occasions so it's a good-to-know technique. You just have to remember when you're using the rendered output you can't use hover/identify to get values because now it's RGB or pseudocolour. Sep 18 '14 at 5:55

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