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Author Topic: Stitching dilema  (Read 3796 times)
BernardLanguillier
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« on: December 19, 2005, 11:35:50 PM »
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Dear Stitchers,

One quick question for you.

I have faced a new situation this weekend when shooting a panorama in a temple in Kamakura (Japan):

http://www.photosig.com/go/photos/view?id=1667068

The problem is that there is both articial and natural light in the scene, for which different WB settings should ideally be used in order to get accurate colors, or at least perceptually reasonnable colors.

The image above, stitched with PTGui 5.5 was assembled from .nef files converted with RSP using the default camera AWB value (ranging from 5000 to 5400 K, almost stable), which doesn't quite correct for the yellowish tints in the center part of the frame.

Thanks to this slight difference in colors, PTgui is able to stitch the images seemlessly, but the image is probably too yellow in the center (although it did feel yellow in the actual scene). What do you think?

I could have lowered the WB value in the center part of the frame, but I am afraid that PTgui might not have been able to correct for the resulting differences in colors across frames (I haven't tried it yet).

I was wondering what you guys typically do in such cases?

Thank you in advance,

Cheers,
Bernard
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photopat
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« Reply #1 on: December 20, 2005, 02:20:28 AM »
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Since there isn't that "much" color in the image exept the red carpet and the warm hue from the lamp hitting the timber (and the red carpet).
Just by making a hue/saturation layer and lowering the overall saturation with about -20 (with or without layer mask for the rest of the image)will make a "smother" image.
Maybe I would lower the sat value of yellow a bit to,but that's more to a personal taste.
 
I personally wouldn't do much more with this Image(but that's my taste) since I like to keep a bit of the "yellow tint" from indor lightning(feels more natural to me)

So my answer would be to fix it in PS were you have much more control of the out come rather than
trying to fix it in the "stiching" stage.You might  just end up with more trouble

Patrick.
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francois
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« Reply #2 on: December 20, 2005, 03:43:06 AM »
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Quote
....
The problem is that there is both articial and natural light in the scene, for which different WB settings should ideally be used in order to get accurate colors, or at least perceptually reasonnable colors.

The image above, stitched with PTGui 5.5 was assembled from .nef files converted with RSP using the default camera AWB value (ranging from 5000 to 5400 K, almost stable), which doesn't quite correct for the yellowish tints in the center part of the frame.
.....
I could have lowered the WB value in the center part of the frame, but I am afraid that PTgui might not have been able to correct for the resulting differences in colors across frames (I haven't tried it yet).

I was wondering what you guys typically do in such cases?
....
[a href=\"index.php?act=findpost&pid=53951\"][{POST_SNAPBACK}][/a]
Bernard,
I have been doing some sort of WB blending with a few of my images.
I process my RAW file(s) with different WB settings, then I bring them as layers in Photoshop and work with masks. The main problem is trying to blend seamlessly different light sources, they tend to contaminate each other.
 I don't think that your image needs it, really!
« Last Edit: December 20, 2005, 03:43:44 AM by francois » Logged

Francois
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« Reply #3 on: December 20, 2005, 07:06:32 AM »
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Thank you for the advice gentlemen.

Regards,
Bernard
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Eric Myrvaagnes
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« Reply #4 on: December 20, 2005, 10:31:29 AM »
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Bernard,

I agree with all of the previous advice. I like the image just the way it is, but I could probably accept a little desaturation in the middle section.

It bothers me when I see an image that was obviously taken in mixed light but the photographer has adjusted WB in various parts so that the scene looks as if there was only one kind of light source. To me, that looks artificial, and I don't like it as much.

Yes, when we see a scene (real world, not in camera) in which there is mixed lighting, the brain compensates somewhat, but the incandescent parts still look warmer and yellower than the daylit parts.

That is a lovely picture, by the way.

Eric
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DiaAzul
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« Reply #5 on: December 20, 2005, 11:09:48 AM »
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I quite like this image, though the central 'tungsten' part is too dark and lacks contrast.

I would be tempted to add a colour balance layer, mask out the daylight sections then with the midtones go towards yellow (from blue) and also to red (from cyan), leave green. Then for highlights do the opposite - go more blue, more cyan. This will brighten the central section and increase contrast whilst still retaining the tungsten warmth.

Overall, keeping the tungsten lighting in the centre helps to keep the attention where it should be - on the subject - and I don't see there is a conflict in having a varying lighting types across the image if that is what was in the room at the time (though the changes above will help to integrate it better into the overall image - IMHO).

Ciao ciao
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francois
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« Reply #6 on: December 20, 2005, 11:42:27 AM »
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Quote
...It bothers me when I see an image that was obviously taken in mixed light but the photographer has adjusted WB in various parts so that the scene looks as if there was only one kind of light source. To me, that looks artificial, and I don't like it as much.

Yes, when we see a scene (real world, not in camera) in which there is mixed lighting, the brain compensates somewhat, but the incandescent parts still look warmer and yellower than the daylit parts...[a href=\"index.php?act=findpost&pid=53979\"][{POST_SNAPBACK}][/a]
Well said Eric! I do it only when different light sources degrade the image too much or when it doesn't look natural. I try to keep my images as natural looking as possible and only use the WB blending technique on a handful of photos.
« Last Edit: December 20, 2005, 11:43:19 AM by francois » Logged

Francois
jdemott
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« Reply #7 on: December 20, 2005, 12:00:54 PM »
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Bernard,

I tend to approach stitching as a fairly "mechanical" process in which one must follow all the rules quite rigidly in order to get the best results.  That means using identical exposures with identical WB settings for all images in order to get the best results in the stitching and blending process.  I then make the more "creative" adjustments in Photoshop working on the blended file.  

In this particular case, I think I would prefer to see the WB corrected so that the colors in both the center and the sides of the photo appear accurate (although I think the approach in the photo you posted is also valid).  There are several avenues that you could take to get overall color accurate throughout the scene.  I think the most precise approach would be to save the stitching parameters and repeat the stitching process with another set of files that have a different WB setting.  (This is easy to do in PT Assembler and I assume it is similar in PTGui.)  You would end up with two versions of the overall scene that are identical except one would have a WB setting in the Incandescent range and one would have a WB setting closer to Daylight.  Then you simply layer the two files, create a layer mask, and apply a gradient to the layer mask so that the Daylight layer is visible at the sides and the Incandescent layer is visible in the center.  A simpler approach would be to create only one stitched file using an Incandescent WB setting (i.e., optimized for the center) and then apply a warming Photo Filter to it in Photoshop, again using a layer mask so that the warming effect is applied only to the edges.
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John DeMott
BernardLanguillier
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« Reply #8 on: December 20, 2005, 04:58:04 PM »
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Thank you all for the additional advice.

I'll try the 2 approaches that you advised, the double stitching overlaying probably having the most potential for scene more difficult than this one.

Regards,
Bernard
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Jonathan Wienke
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« Reply #9 on: December 21, 2005, 05:36:01 PM »
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The problem is that there is both articial and natural light in the scene, for which different WB settings should ideally be used in order to get accurate colors, or at least perceptually reasonnable colors.
There are only two ways to really solve this:

1. Convert everything to B&W before stitching. But this can be a cop-out.

2. Perform the stitch twice. The first time, stitch TIFFs that have been converted from RAW using a WB setting appropriate for the natural light. Make another set of TIFFs converted with the same settings except a WB appropriate for the artificial light, and stitch then using the exact same stitch settings as the first set of TIFFs. Paste one stitch on top of the other in Photoshop, and blend them together by making a layer mask and airbrushing it so that the composite has a "correct" white balance everywhere. Place the layer with the greatest area of correct white balance on top, and then airbrush holes in it to expose the layer under it as appropriate. Select a brush hardness of 0, and adjust the brush diameter to control the sharpness of the transition from one layer to the other.

I used Technique #2 in this image. While it is a single capture rather than a stitch, it has 5 light sources, which required me to process the RAW 5 times, and then blend the 5 different layers together instead of just 2 layers.

« Last Edit: December 21, 2005, 05:41:44 PM by Jonathan Wienke » Logged

BernardLanguillier
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« Reply #10 on: December 21, 2005, 05:48:24 PM »
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Thanks Jonathan.

If my understanding is correct, your proposal is the same made above by jdemott and it appears to be the best option.

I just need to figure out how to do the exact same stitching with a different set of images with PTgui, which shoudl be doable.

Regards,
Bernard
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jmb
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« Reply #11 on: December 22, 2005, 08:43:44 AM »
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I just need to figure out how to do the exact same stitching with a different set of images with PTgui, which shoudl be doable.

I don't know about PTgui, but with PTAssembler, simply add the extra images into the project file (along with any control points, etc) and reoptimize the project. If you output the file as a multilayer PSD file, you can simply edit the masks on the photos with the WB problems and you should be done.

Alternatively (and this actually might be easier now that you are already done stitching the file...), you can reprocess the RAW images with the WB problems, name them the exact same thing as your earlier images (in a different directory), go back to your PTgui project file, delete all the pictures from the project that didn't have any WB problems (you don't need them, and provided you don't reoptimize the project after deleting them, you will end up with a file the exact same dimensions as the file you created earlier, and the images with the WB problems will be in the exact same spot as before). After letting PTGui create the file, you can simply bring it into PS, layer it with your original file, and mask out the parts you don't want.

I hope this helps/makes sense,

JMB
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Jonathan Wienke
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« Reply #12 on: December 22, 2005, 09:05:54 AM »
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There's actually an easy way: simply give each set of converted TIFFs the same name set, but put them in different folders. Perform the stitch on the first set, then move the source TIFFs and the stitched output to another folder, and move the second set of source TIFFs into the stitching folder, and re-execute the stitch without changing any settings or options in the stitching project. Repeat these steps for each additional WB version of the source TIFFs you may have. Then all you have to do is layer and blend the stitches in Photoshop.
« Last Edit: December 22, 2005, 09:07:36 AM by Jonathan Wienke » Logged

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