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

• Floatingpoint to 16 bit (integer)
• Floatingpoint to 32 bit (integer)
• 8 bit to 16 bit (integer)
• 16 bit to floatingpoint
• 4 bit to 8 bit
• 1 bit to 8 bit

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