Using the Convert Pixel Type process

The Convert Pixel Type process allows you to convert the pixel type of an image from 1-bit depth data to another. The pixel type (also known as bit depth) of a cell determines the range of values that a particular raster file can store, which is based on the formula 2n (where n is the bit depth). For example, an 8-bit raster can have 256 unique values, which range from 0 to 255.

This process is generally used to convert an input image to the required pixel type. It can also be used to convert 16-bit or 12-bit imagery to 8-bit imagery, although generally the Stretching process is used for this conversion instead.

The following table shows the range of values stored for different bit depths:

Bit depth

Range of values that each pixel can contain

1 bit

0 to 1

2 bit

0 to 4

4 bit

0 to 16

Unsigned 8 bit

0 to 255

Signed 8 bit

-128 to 127

Unsigned 16 bit

0 to 65 535

Signed 16 bit

-32 768 to 32 767

Unsigned 32 bit

0 to 4 294 967 295

Signed 32 bit

-2 147 483 648 to 2 147 483 647

Floating-point 32 bit

-3.402823466e+38 to 3.402823466e+38

The range of values stored for different bit depths

The supported conversions include

You can also take advantage of applying an offset and scale pixel values.

Pixel Value = (Pixel Value + Offset) * Scale

You can use these to convert the pixel values from feet to meters or apply simple transformations on the pixel values. This process can also be used to convert a terrain model's values from ellipsoidal height to orthometric height by applying an offset to shift the values.

You can also set a value that will be converted to a NoData value.

It should be noted that floating-point images are read into ArcGIS Image Server by scaling them by 214 and converting them internally to signed 32-bit long values.

signed 32 bit long value = 32 bit floating point value * 2

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7/10/2012