Sample image to 8-bit or 16-bit format using the Sample to 8 / 16 bit tool. Each pixel in the image is then represented by an 8-bit or 16-bit value, respectively.

The current image format is shown in the panel. Here, the Image has 16-bit gray values. Therefore, each pixel contains a gray value between 0 and 65535, which is 216 different values.

Enter the Minimal Gray Value and the Maximal Gray Value for the image to be sampled. These values adjust the gray value range for the 8-bit or 16-bit image.

Select 8 Bits or 16 Bits from the pull-down menu for Sample to Range.

Converting 16-bit to 8-bit format is often done to reduce the large data size of 16-bit images. The gray value range reduces to 0-255 by choosing 8 Bits.

If 16 Bits is selected, the bit depths can be increased from 8-bit to 16-bit.

Click Apply to sample the image using the current settings.

The following images show an example for changing the gray value range in an 8-bit image of a Berea sandstone. Here, the contrast between solid phases (mid and bright gray values) and pore space (dark gray values) increases by reducing the original gray value range to 70-200 instead of 0-255.