Legacy ImageMagick Discussions Archive

Is there functionality built into image magick that allows a user to generate an HDR image similarly to how PhotoMatix generates an HDR image? For example, can I generate an HDR image with three images, two of which are over and under exposed? PhotoMatix works by taking a set of over/under exposed images to generate an HDR image that can be tone mapped. I am not sure how this is done.

Do you use the composite and blending commands?

I'm sure this has been covered in a post, but I'm probably just missing it in my search.

Thank you.

I have never used HDRI images (in raw format?) before, but I would suspect that it would be possible to approximate that operation if someone knows exactly how they combine them. I am sure there are tutorials on the web for that. The main point here I believe is that you will need to be in IM HDRI compile mode to get the best advantage of the dynamic range of those kinds of images.

Yes, I compiled IM with HDRI support as well as EXR support. So I can actually read/write HDR images and I understand that my color range is now represented with 16bits of information which is what I need when I shoot in raw. But the HDR image generated with PhotoMatix using exposure bracketing is what I'm going after and I thought I might be able to replicate that functionality using Imagemagick. I havent found anything quite yet.

Thanks

I am sure I have seen tutorials on the web by searching google. Have you done that? I will have to see what I can find when I can.

There are lots of tutorials I found by searching google with "combining HDRI images".

See for example
http://www.photoshopcafe.com/tutorials/ ... hdr-ps.htm
http://www.cambridgeincolour.com/tutori ... -range.htm

From what I see, it is likely that you need to adjust each image using combinations of gamma or brightness/contrast, saturation, and sharpening or blurring, tone mapping as desired. My guess is some information is in the headers of the files, such as EXIF data. Then my guess is it is probably an averaging of the images together in some weighted manner. In IM, there is -evaluate-sequence mean (-average still works but is deprecated) that does an equal weighted average. There are other compose methods that allow you to blend or dissolve two images at a time.

The hardest part is to take images that perfectly overlap or be able to adjust them to do so. IM has -roll that lets you shift by integer pixels or -distort SRT that allows partial pixel shifts. There is also compare that lets you find where one smaller image best matches to a larger image. That would let you find the best whole pixel shift to align the images.

However, this process really needs an interactive manipulation and display so you can see the changes to each image as you apply them. IM is not really that tool as it is mostly a command line tool. You have to do it all, then display the result and try again if you don't like it.

I doubt you will find anyone who knows exactly how Photomatix works if it is commercial software. One might get some clues from the control panel about what kinds of processing it does. However, one would have to do a lot of testing to find combinations of preprocessing and combining to duplicate that and one would also have to have that software to check against its results. Unfortunately, I don't have it to see the controls, so probably cannot help there.