16-bit grayscale TIFF

Question

What is the 16-bit gray TIFF bit format? I read that only 10 bits actually contain intensity data - is that true? When I try to open 16-bit TIFF in Matlab using imshow (), the image is completely black, but the same image reduced to 8 bits looks great.

Answer 1

If the creator of the TIFF writes a well-managed TIFF, each channel must be normalized to the full dynamic range of that channel. In other words, 16 bits per channel should be in the range from 0-65535, 8 bits per channel should be in the range from 0 to 255.

While the number of bits used could be encoded into a tag, there are no basic tags that encode it. This means that if a 10-bit device does not normalize to 16 bits, there is no way for the basic reader to understand the intent of the image.

As a third-party note, there are other image file formats (Dicom - one) that provide a way to express how many bits per channel are significant.

Answer 2

How many bits are used, a lot depends on the camera that took the picture. A 14-bit camera will use 14 out of 16 bits, a 10-bit camera will use 10.

If you display the image by calling imshow(img) , everything will be black if the full dynamic range of the image is not used, since imshow will scale to the dynamic range (i.e. from 0 to 2 ^ 16-1). If instead you type imshow(img,[]) , which scales the image to minimum / maximum, the image will be displayed beautifully.