Any Way to Test For Image Bit Depth?

[skithebird]

We're using a ZWO ASI183GT camera and have set SharpCap's Colour Space for MONO16 with a full sized (5496x3672) capture area. We've taken hundreds of snapshots in *.png output file format. Each saved image is about 20 MB in size, but occasionally we've noticed a smaller sized file saved (~10 MB). Although our light distribution images appear visually much as we've expected them to, a more detailed analysis of our background images has revealed that we're not achieving the full 12 Bit image depth we expect with our 12 Bit ASI183GT camera. All our images appear to only have 8 Bits of dynamic range. We've tried saving our images as TIFF and FITS, but still see the same 8 bit image data limitation. When we use the Pixel Tool to assess a very low light black-state background image with a peak signal of 48 counts, we've noticed that the counts at each of the surrounding pixels appear only in increments of 16. When then chose a slightly higher level background image with a peak of 128 counts, and we saw the surrounding pixel peaks as 80, 64, 112 and 96, all differences in increments of 16. Everywhere. We assume we're doing something wrong somewhere in our image capture process flow or SharpCap settings. We've developed a particular high dynamic range image analysis method for displaying our light distributions. But this method requires that we are using 12 Bit images, and is ineffective with only 8 Bit images. What can we do to be sure we are capturing full 12 Bit images? Are we missing a setting? And is there a better test of Bit depth than the Pixel Tool we're using? Thanks Robin. Bob

[skithebird]

Ooooops. Please ignore. I pulled this trigger too fast. The mistake was caused by a coding error on our side. SharpCap is working brilliantly. We do indeed have 12 bit depth. Sorry for this question. Thanks Robin.

[admin]

Hi,

one thing to watch out for is that lots of image processing software and libraries will happily read high bit depth images in PNG/TIFF format, but will quietly reduce them to 8 bits as they are loaded

It took me quite a while to make sure that SharpCap can both save and load high bit depth images in these formats with no loss of fidelity.

Thanks, Robin

[skithebird]

Thanks Robin! Good to know. And that makes me feel a little better. We're using ImageJ for our processing, and it's usually pretty reliable. Our coding error was the culprit this time, accidentally forcing ImageJ to read and display only 8 bits. Hope you had a Happy Thanksgiving. Bob