[HDR-photo] Starting out...

[Royce Howland]

John Callan wrote:
> Hello everyone
> My name is John Callan and I am a photographer working in France.

Welcome!

> At the moment I am using CS2/Bridge from where I select images and
> import them into "Photomatix". I then stitch them together with Realviz
> stitcher. The results are okay but I just know that I'm doing it wrong !!
> Any help or advice no matter how small would be very gratefully received.

First off, if the end result looks good to you then you can't be doing 
things too "wrong". :) However there may be some room for technical or 
workflow improvements.

There are three main ways to tackle the process for HDR panoramics:

1. HDR first, then stitch, which you are doing now. Since stitching can 
be a beast on low contrast images, this avoids the problem by stitching 
only once on the final resulting tone mapped image which likely has good 
contrast through-out. The down side is that tone mapping may produce 
contrast and color variations in each individual frame, even if the 
original exposures were all taken on manual with identical shooting 
parameters. If so, then the stitcher may not be able to blend regions 
very well and the final image may look like a patchwork of different 
hues and tones. Not much you can do about this except a lot of 
painstaking corrective work in Photoshop.

2. Stitch first, then do HDR. As mentioned in #1, stitching low contrast 
images can be a pain. Depending on your image bracket sequence, you 
probably have at least two low-contrast series -- the most underexposed 
series, and the most overexposed series. Some stitchers support running 
multiple stitch projects of different input files using the same control 
points and other parameters. If you have one of those stitchers, you can 
use the image sequence with the best over-all contrast (hopefully it has 
good contrast in all important areas) as your first project to set up 
all control points and blending parameters. Then use that project file 
to stitch all of the remaining series. Once all stitches are done, do 
the HDR processing once on the pano's, and all tone and color work 
should look as seamless as possible across the field of view. The 
downside is that if the control point set ends up not being a good match 
for all of the bracketed series, you won't find out until you've tone 
mapped and see ghosts, shadows and other irregularities where the 
original stitches don't overlap precisely. Then you have to go back to 
the control points and fine tune them, then re-process everything from 
the beginning.

3. HDR and stitch in one go. As far as I know, only Autopano Pro 
supports this option right now. You can feed it your entire set of 
bracketed pano images, and it will stitch and merge them all into an HDR 
image, then output a tone mapped file. If you prefer to use a different 
HDR tool for merging and/or tone mapping, you can configure Autopano to 
emit separate TIFF images, one for each exposure value. The benefit of 
this over #2 seems to be improved accuracy since the stitch can take all 
frames into account at once. Plus you're only doing the stitch once, so 
fewer opportunities for a "user error" to cause a problem and have to 
start the whole thing over.

In the past I have normally used #2 with Panorama Factory, and a lot of 
work fine tuning my stitch parameters -- sometimes having to run the 
process from start to finish more than once. Lately I've been evaluating 
#3 and probably will switch to Autopano Pro as my main stitcher.

I have discussed #1 and #2, as well as HDR topics in general using 
Photoshop and Photomatix, in an article found here:
http://www.naturescapes.net/072006/rh0706_1.htm

Royce Howland