如何在 ImageJ/Fiji 中获得透明背景

Question

I have a hexagonal image, stitched together from several single images, which is saved as a rectangle 8bit TIFF with black corners. I want to set the black corners to transparent. Because I want to stitch several hexagons together. I tried already the threshold function and set the black areas to NaN but after reopening the image the corners were still black. I also tried making a selection and clear outside which resulted in a white background. I need to save it as a TIFF file again for further processing. Does somebody has an idea how to solve that issue?

Answer 1

8-bit images do not support transparency, only integer values from 0 to 255.

If you want to use NaN, you must first convert to 32-bit float ( Image ▶︎ Type ▶︎ 32-bit ). It is possible to save a 32-bit float image as TIFF—but note that many TIFF viewers (eg Preview on macOS) will not display it nicely.

One way to set values to NaN is to use the Process ▶︎ Math ▶︎ Set... command, after making a selection. Everything in the selection will become NaN.

Answer 2

I think it is not possible because NaN or 0 as suggested By ctrueden gives a black background (does not delete it). This require alpha channel to do so as it is the case in other software as GIMP (add alpha channel, select the background, delete. Hope this is useful !