topic Re: Change pixel value in raster file in Data Management Questions

Change pixel value in raster file

RupsaBhowmick — Tue, 11 Jul 2017 16:20:22 GMT

How do I change pixel value in a raster dataset?

Re: Change pixel value in raster file

ChrisDonohue__GISP — Tue, 11 Jul 2017 16:38:18 GMT

If you have access to the Spatial Analyst extension, one way is to use the Conditional geoprocessing tools

An overview of the Conditional toolset—Help | ArcGIS for Desktop

You can also access the Conditional (Con) functions in Raster Calculator:

Raster Calculator—Help | ArcGIS for Desktop

There are some other possibilities, but it depends on what you would like to do. Can you provide more details on what you are trying to change?

Chris Donohue, GISP

Re: Change pixel value in raster file

RupsaBhowmick — Tue, 11 Jul 2017 16:44:17 GMT

Thank you Chris for your reply. I have one MODIS aerosol optical depth data. The raster file have 0 to 254 rowid and 1 to 255 pixel value. The 0 has marked as no data and 255 marked as maximum value. But actually, 0 has value and 255 has no value. I have change the 255 as null and add 1 to all other value to get correct pixel values.

Can you help me to solve this problem?

Re: Change pixel value in raster file

ChrisDonohue__GISP — Tue, 11 Jul 2017 16:51:44 GMT

For the Null issue, consider using SetNull (Spatial Analyst):

Set Null—Help | ArcGIS for Desktop

Example from the Help:

Using an Expression:

To set any cell with a value greater than 5 to NoData and have the remaining cells retain their original values, the following parameters could be used on the tool dialog box:

Input conditional raster : InRas1
Expression : "Value < 5"
Input false raster or constant value : InRas1
Output raster : setnull_1

The equivalent using an expression in Map Algebra is as follows:

OutRas = SetNull(InRas1 < 5, InRas1)

Source: Setting values to NoData with Set Null—Help | ArcGIS for Desktop

As to incrementing the other values up by one, I believe the Raster Calculator would be the way to go, using Map Algebra.

What is Map Algebra?—ArcGIS Help | ArcGIS for Desktop

Example from the Help:

Operators can accept a mixture of rasters and numbers. For example, the following adds a constant value of 8 to all the cells in the input raster:

outRas = Raster("inras1") + 8

Source: A quick tour of using Map Algebra—ArcGIS Help | ArcGIS for Desktop

Chris Donohue, GISP

Re: Change pixel value in raster file

RupsaBhowmick — Tue, 11 Jul 2017 17:04:24 GMT

ok, great. I need to change the pixel values through model builder as I have many AOD raster files so I have to run a loop. so how to change the pixel values in a loop in model building.

Re: Change pixel value in raster file

ChrisDonohue__GISP — Tue, 11 Jul 2017 17:25:41 GMT

The trick to processing all the rasters is to employ an Iterator in Modelbuilder. This will allow the looping through of each raster.

Here's the Modelbuilder Iterators:

A quick tour of using iterators—Help | ArcGIS for Desktop

Accessing iterators in ModelBuilder—Help | ArcGIS for Desktop

Example of using an iterator in a model—Help | ArcGIS for Desktop

Note, however, if you are conversant with Python, that would probably be more effective than using Modelbuilder (Modelbuilder can be a bit quirky).

Chris Donohue, GISP