# convert 16 bit image to 8 bit image

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mohd on 5 Mar 2012
Commented: Tiziana on 21 Nov 2022
how to convert 16 bit image to 8 bit image

Jan on 5 Mar 2012
The uint16 image used values from 0 to 2^16-1, while the uint8 images use a range from, 0 to 2^8-1 only. If you just cast the original values to uint8, the saturation will destroy a lot of information. Better use:
img8 = uint8(img16 / 256);
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dror yemini on 10 Sep 2020
yes but you loase somthing better before take bits with information so maybe do equalization of histogram before conversion ?

Rasmus Herlo on 11 Feb 2021
OBS: Jan's answer will do absolutely fine, if your image is optimized to use the entire scale. However, if your pixel values are only occupying a fraction of the available bits (common in much imaging), the direct conversion will lead to a significant loss of information. In addition, you might want to get your image on 1:2^16 (instead of 0:2^16-1) before normalizing.
Image conversion in software like ImageJ therefore uses linear scaling, and one would typically apply a similar approach here, by:
Input: Im16 'uint16' (any 16bit image)
dbIm16 = double(Im16)+1
dbIm16 = min(dbIm16(:)); db16max = max(dbIm16(:));
TgBit = 8; % or any other lower bit scale
% example with 16bit to 8bit
Norm_wOffSet = dbIm16/db16max; % maintaining putative offset from 0 in the data
Im8_wOffSet = uint8(Norm_wOffSet*2^TgBit-1); % back to 0:2^8-1
Norm_woOffSet = (dbIm16-db16min)/(db16max-db16min); % Scales linearly to full range
Im8_woOffSet = uint8(Norm_woOffSet*2^TgBit-1); % back to 0:2^8-1
Tiziana on 21 Nov 2022
Thank so much for your answer. Could I ask you the reasons of this "you might want to get your image on 1:2^16 (instead of 0:2^16-1) before normalizing"? Thank you very much.

Wayne King on 5 Mar 2012
You can use uint8() to cast the image into unsigned 8-bit integers. Or int8() for signed 8-bit integers.
X = uint8(ones(10,10,'uint16'));
class(X)

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