jimmyd
Posts: 72
Location: United States
Registered: 6 Nov 2004
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Color matching on a handheld nadir.
Posted: 7 Aug 2008 at 21:09 GMT
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I use John Houghton's PTgui Viewpoint technique when blending in the nadir hole against more problematic scenes such as hardwood floors, bricks, etc. I actually get really good results stitch wise by following the tutorial. My problem is that my hand held nadir shot is slightly off in color because I have to change ISO & exposure to get a fast enough shutter to avoid movement blur. So in short, the match is off enough that you notice the color diff when panned down.
What is a good way to match the color of the floor around the nadir? Should I manipulate before I use the handheld in PTgui or should I do some touchup after pano is complete on the nadir cube?
As I mentioned, I like the results I get by using Viewpoint because it allows me stitch difficult floors. Something the patch tool (which nicely matches color and contrast for you) cannot do.
Thanks in advance.
James
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Hans Nyberg
Posts: 866
Location: Denmark
Registered: 28 Aug 2005
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Re: Color matching on a handheld nadir.
Posted: 7 Aug 2008 at 21:29 GMT
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Your most important step is your Raw conversion, (Of course you shoot Raw)
In Camera Raw you can easy do a white balance on your nadir so that you get very close to the other images. Use the Color Picker to sample the RGB values on some of the areas you have also in your nadir shot.
You can than easy correct the nadir to match the other images.
Hans
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Bradford Bohonus
Posts: 80
Location: United States
Registered: 29 Jan 2008
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Re: Color matching on a handheld nadir.
Posted: 7 Aug 2008 at 21:51 GMT
updated: 7 Aug 2008 at 21:55 GMT
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jimmyd said: Should I manipulate before I use the handheld in PTgui...
yes, this would be a good method.
Do some noise reduction on the image and color correction on the handheld shot to match the others as close as you can (do this with the image in 16bit mode in photoshop, then bump it back to 8bit if that is what you are stitching). The blending process during stitching will help smooth things out.
Repeat the process if there is still a noticeabe difference after stitching and blending.
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jimmyd
Posts: 72
Location: United States
Registered: 6 Nov 2004
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Re: Color matching on a handheld nadir.
Posted: 7 Aug 2008 at 23:40 GMT
updated: 7 Aug 2008 at 23:41 GMT
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Hans Nyberg said: You can than easy correct the nadir to match the other images.
That is what I am asking, what literally is the process in Photoshop. I have CS3 and yes, I shoot in raw. BTW, both images are shot with the same whitebalance. The difference is relative to exposure due to the need to speed up the shutter on the handheld shot.
I get it close (to what my eye sees as close) but it is still noticable in the fishished pano. I ma just looking to better this last step.
Edit: The stich blend is perfect, it is the color match that I can't quite get.
Thanks again....
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halflife
Posts: 145
Location: Romania
Registered: 3 May 2006
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Re: Color matching on a handheld nadir.
Posted: 8 Aug 2008 at 5:52 GMT
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jimmyd said: I use John Houghton's PTgui Viewpoint technique when blending in the nadir hole against more problematic scenes such as hardwood floors, bricks, etc.
James
Hi,
Sorry for not answering to your problem and instead asking a question: can you provide a link to this tutorial?
Thank you a lot!
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gus
Posts: 388
Location: United Kingdom
Registered: 19 Jun 2007
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Re: Color matching on a handheld nadir.
Posted: 8 Aug 2008 at 6:02 GMT
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Hi James,
The whole point of the viewpoint correction tool is to take an oblique shot with the camera ON the tripod, but at an angle. Just move the tripod a meter or so away, point it at the nadir and use the same settings as the other shots. This saves time becuase, firstly, you dont need to play around with the settings to get a fast shutterspeed, and secondly, no post-processing is required to match the colours.
Gus
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John Houghton
Posts: 2317
Location: Hitchin, United Kingdom
Registered: 17 Jan 2005
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Re: Color matching on a handheld nadir.
Posted: 8 Aug 2008 at 6:57 GMT
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gus said: The whole point of the viewpoint correction tool is to take an oblique shot with the camera ON the tripod, but at an angle.
Gus, The whole point is to correct shots not taken from exactly the same point as the main tripod shots, and as Joost says in the introduction to his tutorial: "It is particularly useful when including a handheld nadir image in a panorama taken from a tripod". The nadir shot doesn't always match in terms of colour and brightness for a variety of reasons. Outdoors, the light can vary between shots. Indoors, there may be multiple light sources and varying shadows can be a problem. For a shot taken at an oblique angle, the different reflectance of a shiny floor can cause mismatches. You might also have a mismatch caused by light falloff at the bottom of the horizontal images as compared to the nadir patch taken from the brighter central part of the image frame. Another problem can be a mismatch in terms of image sharpness, i.e. blending the sharp nadir patch from the centre of its frame with poorer quality at the bottom edges of the horizontal images. The blender may or may not take all these problems in its stride automatically, but I frequently resort to blending the VP corrected nadir in manually with the help of PTEditor in order to get the optimum result I want.
Eugen: My VP tutorial is at www.johnhpanos.com/ptgvpt.htm
John
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jimmyd
Posts: 72
Location: United States
Registered: 6 Nov 2004
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Re: Color matching on a handheld nadir.
Posted: 8 Aug 2008 at 14:48 GMT
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Thanks guys,
However, if I follow John's tut he clearly shoots a nadir from the the same position as the other 2 tripod nadir shots. I believe this was acheived handheld with the majority of the shot alpha masked out leaving only a small area around the nadir hole to deal with. On outside shots you may be able to get the handheld nadir without altering your settings to compensate for camera shake. Inside it can be a little different.
I shoot with 8mm Sigma @ F8, ISO 400(indoor ISO) in a 3 bracket series for all tripod shots. That's 5 around, 1 up, 2 down at 180 rotation, and lastly the handheld. There are 2 problems.
A) I HAVE to adjust the ISO on the handheld to get a proper exposure, hence speeding up the shutter. So post editing becomes a must.
B)Knowing ahead of time what levels to be at is difficult because remember the handheld shot will ultimately be inserted into the result of the BRACKETED shot and not a single shot that I can attempt to duplicate on the scene.
For this reason I have asked the original question of what methods do you guys use in color matching the handheld with the other blended nadir shot?
If one uses PhotoShop, could you provide a quick detail to the procedure or a link? I have CS3, but am completely new to more advanced ideas of photo editing. However, I am really good at "monkey see, monkey do" so if someone would be willing to take the time to briefly lay this procedure out I would be greatly appreciated.
Thank you,
j
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John Houghton
Posts: 2317
Location: Hitchin, United Kingdom
Registered: 17 Jan 2005
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Re: Color matching on a handheld nadir.
Posted: 8 Aug 2008 at 18:23 GMT
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jimmyd said: if I follow John's tut he clearly shoots a nadir from the the same position as the other 2 tripod nadir shots.
Actually, it's clear that it was an oblique handheld shot. The Image Parameters tab shows that the VP tilt angle was about 23 degrees.
I have asked the original question of what methods do you guys use in color matching the handheld with the other blended nadir shot?
From the final project file, I generate two equirectangular panorama images. One is a stitch of all images, excluding the handheld nadir. The other includes only the handheld nadir.
From these two equirectangular images, I extract firstly a nadir view from the handheld nadir image, using PTEditor. (You can use whatever method you prefer). Secondly, I extract an identical view from the main panorama image (using the same sequence of up,down,left,right key presses).
The first nadir view is layered on top of the second view in CS3. They should align very well.
Make a selection around the approximate area to be patched in, and then add a layer mask to the top layer, choosing the "reveal selection" option.
You can now see how well or badly the patch matches the base layer.
Select the image icon in the top layer of the layers palette and use Image->Adjustments->Exposure to improve the match as well as possible using the exposure and gamma sliders. (At no time make any changes at all to the bottom layer).
If appropriate, use Image->Adjustments->Hue/Saturation to tweak the colour to improve the match still further. Use Curves to make any further contrast/brightness adjustments if required.
You may find that the patch matches perfectly on one side but is too light or dark on the opposite side. Obviously, global adjustments cannot correct this. What you do then is make a graduated selection that favors one side and not the other and then apply the required adjustment. To make the graduated selection, switch into quick mask mode (click the icon near the bottom of the toolbox). Then use the gradient tool to drag a gradient black->white across the patch, ending with white at the side you will want to apply your image adjustment to. You will see a red overlay showing the gradient. Then exit quickmask mode by clicking the icon again. You now have the graduated selection. Apply the necessary adjustment with curves or whatever, and that will be applied to the selected side of the patch, tapering off to nothing at the opposite side. ctrl/d to deselect.
When the patch matches the background well, make adjustments to the layer mask to define the precise route of the seam. Blur the mask (in whole or in part) to produce feathering, if required, to give a seamless join.
Flatten the image and save. Insert the result back into the main panorama with PTEditor (or rebuild from cubic tiles etc).
Alternatively, a quick method should be to make use of Edit->Auto-Blend Layers after selecting the two layers in the Layers palette. I haven't made much use of this method myself, but others have reported good results.
John
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jimmyd
Posts: 72
Location: United States
Registered: 6 Nov 2004
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Re: Color matching on a handheld nadir.
Posted: 8 Aug 2008 at 18:33 GMT
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Thank you John, this is very helpful. I also like using PT editor to extract the nadir view but have noticed that it will not open a tiff file over a certain size. I get the impression you produces high rez pano's so how do you work around this?
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John Houghton
Posts: 2317
Location: Hitchin, United Kingdom
Registered: 17 Jan 2005
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Re: Color matching on a handheld nadir.
Posted: 8 Aug 2008 at 19:31 GMT
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I limit myself to editing equirectangular images of no more than 8000x4000. The actual limiting size is a bit vague. PTEditor can extract views ok but seems to have trouble inserting large views into large panos: it goes through the motions but there's nothing to show for it at the end of the day.
John
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jimmyd
Posts: 72
Location: United States
Registered: 6 Nov 2004
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Re: Color matching on a handheld nadir.
Posted: 8 Aug 2008 at 19:41 GMT
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At 6000X3000 I cannot get PTeditor to open my pano in tiff.
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gus
Posts: 388
Location: United Kingdom
Registered: 19 Jun 2007
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Re: Color matching on a handheld nadir.
Posted: 9 Aug 2008 at 6:14 GMT
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James,
Can I ask why you shoot 2 downward shots at 180° to each other plus a handheld shot----and then use the viewpoint correction tool to stitch the nadir?
Have you tried just shooting an oblique nadir, with the tripod moved away a meter or so, and using the viewpoint correction? Without the 2 downard shots?
The reasons John gave for possible situations where the nadir image requires postwork are valid, but personally I have NEVER had to edit my nadir shots to match colour etc.
The blender sorts it out.
It just seems like a waste NOT to use the viewpoint correction tool for what it was designed for....
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John Houghton
Posts: 2317
Location: Hitchin, United Kingdom
Registered: 17 Jan 2005
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Re: Color matching on a handheld nadir.
Posted: 9 Aug 2008 at 7:01 GMT
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jimmyd said: At 6000X3000 I cannot get PTeditor to open my pano in tiff.
Are you loading PTEditor with a command that increases the memory assignment? See this thread: www.panoguide.com/forums/qna/5182/
John
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jimmyd
Posts: 72
Location: United States
Registered: 6 Nov 2004
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Re: Color matching on a handheld nadir.
Posted: 9 Aug 2008 at 15:42 GMT
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John,
Once again thank you...that fixes the problem!!
Gus,
Basically, I was just trying out different ways to successfully fill the nadir hole under different circumstances, i.e (hardwood vs carpet vs brick, etc)
The reason that I shoot 2 nadirs 180's is because I was following a tutorial that said to. Considering it takes 45 secs more to shot and makes the nadir hole smaller in the end (a def plus) I figured why not. My confusion was on the proper use of the viewpoint feature. Thank you for pointing this out.
Nonetheless, my overall question was how one gets a proper color blend when inserting the handheld shot into the nadir hole. Clearly the patch tool works for when you don't have lines in the floor or patterns. I was looking for advice for more problematic floors.
James
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