banding when stitching RAW files

[Al]

I have the latest PTgui Pro version. I'm using Windows 7, 64 bit O.S.

When I stitch RAW files together, I noticed that there are areas of
each image that have an increased brightness to them. It looked like
the image is washed out. The stitching goes fine, with all the
control points, but the blending is not working at all.

If I first convert the image to a TIF, then the blending looks
correct.

I used to be able to blend directly from the RAW file (CR2) with
previous versions (approximately 3 or 4 versions back....can't
remember exactly).

What could causing this blending issue?

Thanks.

[Erik Krause]

Al wrote:

> When I stitch RAW files together, I noticed that there are areas of
> each image that have an increased brightness to them. It looked like
> the image is washed out. The stitching goes fine, with all the
> control points, but the blending is not working at all.

Did you change (optimize, load) the camera response curve?

Would be easier you uploaded your project file (just the .pts without
the images) so we can have a look.

best regards
--
Erik Krause
http://www.erik-krause.de

[Al]

Erik, I'm somewhat of a newbie with PTgui, so I'm not sure what you
mean when you refer to the camera response curve.

I've uploaded the .pts file.

Thanks.

Al

[Erik Krause]

Al wrote:

> Erik, I'm somewhat of a newbie with PTgui, so I'm not sure what you
> mean when you refer to the camera response curve.
>
> I've uploaded the .pts file.

Ok. My suspicion was wrong. You can see the camera response curve on
Exposure/HDR tab, but it wasn't changed from default in your case.

You took the images with a far too large overlap. Images 0, 2, 4 and 7
would cover the whole panorama. This alone probably wouldn't cause any
problems, but you took the images at varying exposure, all at f/8 but
between 2 seconds and 1/3 second exposure time.

Probably you used Av mode on your camera. The PTGui blender tries to
blend those different exposures, which probably creates the washed out
look. When you converted to TIFF the automatic exposure adjustment might
have leveled the differences and you got a better result.

To compensate for this, go to above mentioned Exposure/HDR tab and check
"Exposure correction (for panoramas taken in automatic exposure mode)".

This should correct for the exposure differences, but I'm not sure you
get a good result, since the differences are relatively large. Next time
shoot in M (manual) mode and with fixed white balance. Set an exposure
that doesn't overexpose the highlights you want to have details in and
shoot the whole panorama with this setting.

Also see http://www.ptgui.com/support.html#5_2

[Al]

Erik, thanks for those great suggestions.

It's true that I've got a lot of overlap. Sometimes, in previous
attempts, I thought I had enough overlap, then the program couldn't
find enough control points. It could also be that the orientation of
the image wasn't quite the same as the others.

Yes, I tend to shoot in Av mode, and I can understand why that would
be a problem, especially for images on the end, where there isn't
sufficient light. I'll do as you suggest and switch to M mode, and
also set the WB, though in RAW, I can just change this parameter.

Once again, thank you. I'll implement these suggestions from this
point forward.

Al

> Also seehttp://www.ptgui.com/support.html#5_2

[Keith Martin]

Sometime around 15/12/09 (at 14:10 -0800) Al said:

>I'll do as you suggest and switch to M mode, and
>also set the WB, though in RAW, I can just change this parameter.

One of the most important things to do when shooting imags for
panorama stitching is to work in complete manual mode. For good
results nothing at all must change from one shot to the next;
exposure, white balance, focus, ISO... nothing.

Remember that the end result is supposed to be as if shot in one go.
Shooting with different parts of the eventual single image exposed
differently will cause problems.

k

[Roger D. Williams]

On Wed, 16 Dec 2009 07:59:24 +0900, Keith Martin <ke...@vortex.co.uk>
wrote:

That said, PTgui can also do a remarkably fine job of blending shots
that are deliberately taken a different exposures... It's not only
saved panoramas where I forgot to take the camera off "Auto,"it's
also done well blending a panorama where, for instance, I was
peeking into a dark, covered railway station from a bright, sunny
street... and had deliberately increased the exposure to capture
more detail in the shadows.

If you look closely you can see some rather strange effects on the
ground, but to the casual viewer the result is quite acceptable,
and much better than having an obviously badly underexposed section
of the panorama.

Please understand, I'm not recommending this as an alternative to
purely manual operation, which is clearly better as a general
rule, especially as HDR techniques allow for plausible compression
of image dynamic range. I'm just saying PTgui can help you get away
with it if you break this rule for whatever reason.

Roger W.

--
Business: www.adex-japan.com
Pleasure: www.usefilm.com/member/roger

[Keith Martin]

Sometime around 16/12/09 (at 12:21 +0900) Roger D. Williams said:

>PTgui can help you get away with it if you break this rule
>for whatever reason.

Good point. That's a kind of safety net for when mistakes are made,
whether on purpose or not.

k