Image integration with the option "exposure time"; the metadata

[Fco. Bosch]

I tried to stack several images with the option "exposure time" enabled  in the section "weights". And the processing console  say this:
"Opening files:
D:/imágenes astronómicas/temp/IMG_0002.fit
Reading FITS: 16-bit integers, 3 channel(s), 4770x3177 pixels: 100%
*** Error: D:/imágenes astronómicas/temp/IMG_0002.fit: No way to know the exposure time.
<* failed *>"

1) My *.raw files have the metadata (camera, date and time, exposure time etc) as I can see in the windows explorer, with the view “details”
2) I have saved my *.raw images with PI 1.5 in *.fit format, with the options of "metadata" and all the other enabled.
3) I have added the *.fit files in “image integration” for to stack the images, with the option  "exposure time" enabled  in the section "weights". So every image will contribute to the final image according to their exposure time, I expected. But I received the error above
4) I have searched in the menu “file” the item “FITS header”, and there isn’t  “exposure time” nor other particular data of my shots.
   It is a bug, or I’m unable  to understand the operation of the software?

[Juan Conejero]

Hola Francisco

The problem here is that ImageIntegration relies on FITS header keywords to learn the exposure time. Metadata on file format option dialogs refers to XML image metadata (which, by the way, isn't fully supported by PixInsight yet), but has nothing to do with FITS header keywords.

So what happens is just that your FITS files don't have the EXPTIME or EXPOSURE standard keywords, and hence ImageIntegration is unable to read the exposure time.

For performance reasons, ImageIntegration only works with image formats able to do incremental reading (read image files by chunks of contiguous pixel rows), and currently only the FITS format supports it. This is indeed a problem with DSLR images. The solution is a modification of the BatchFormatConversion script to generate EXPTIME keywords automatically from exposure time metadata read from DSLR raw images (perhaps taking into account ISO values, too?).

I'll try to make this for version 1.5.1. Sorry for the inconveniences. For now, the workaround is to create the EXPTIME keywords manually, but this is of course a lot of work. A better option is to group sets of images with the same exposure, integrate them apart, and then combine the results with PixelMath.