I see extra quantization when displaying a grayscale uint8 image. For example:
inRamp = uint8 ( round ( repmat( linspace(0,60,1200), 600, 1 ) ) ); imshow ( inRamp) imwrite ( inRamp, 'inputRamp.tif' )
If I display this tif image in another display application, I see a series of steps. The image displayed in MATLAB using imshow has a couple of steps that are double-wide and double-deep. I have verified this using Windows screen captures of the image as displayed by other software and as displayed in MATLAB. The plots of this data show a clear stairstep pattern, with the MATLAB showing a couple of steps (near pixel value 10 and 40) that are double width and double height. I can email plots to anyone interested in seeing them.
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After discussing this with Mathworks technical support, I tried changing the renderer used from "painters" to "opengl". This appears to solve the quantization problem.