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Author Topic: Dealing with DOF  (Read 7981 times)

holgar

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Dealing with DOF
« on: February 13, 2015, 02:27:27 PM »
Hello, me again with another Question. I hope I can some day give you some valluable Infos on my experiences back ;-).

I would like to scan small Objects. I am considering buying a Canon EF 50mm/ 2,5/ Makro.
Now the Problem with Marco is certainly the shallow DOF. So I wonder how PS is dealing with blurred parts of the images.

I have made a test with proccessing Focus-stacks with a Software called Helicon Focus. The results where very good in PS. But the Process of taking Focusstack Photos is very long. I would prefer to instead take more Photos from different angles and distances.


If I take enough pictures from different angles I assume I will still get good results even with only small parts in Focus.

Another though I had was to make masks based on Sharpness of the images (Photoshop has such a fucntion). Would that help in PS?

My question is how Ps is dealing with blurred parts? Will big unsharp parts of the image reduce quality? Or are thoose part ignored in Recontruction?

FoodMan

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Re: Dealing with DOF
« Reply #1 on: February 13, 2015, 05:52:53 PM »
good idea.. I would try to mask blurred areas in photoshop..

nadar

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Re: Dealing with DOF
« Reply #2 on: February 13, 2015, 08:13:24 PM »
if you reduce the aperture, DOF will be wider. If your objects don't move, use a good stable tripod and decrease shooting speed to compensate for smaller aperture. I don't think a "macro" lens will behave differently than any other lens on this aspect

bigben

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Re: Dealing with DOF
« Reply #3 on: February 13, 2015, 10:57:35 PM »
I've only done a couple of experiments on a coin but I found it was possibly not necessary to perform the focus stacking, although you would obviously need enough overlap between focused areas of the photos.  PS won't create points from out of focus areas so masking may not have much effect.

JohnyJoe

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Re: Dealing with DOF
« Reply #4 on: February 17, 2015, 09:22:36 PM »
Yeah i have had similiar question... how does photoscan treat if i have a spot on my object in several photos, but on some photos the "spot" (area of object) is blurred (out of focus), but on the other photos (some of them), that area is sharp...? Will photoscan recognize what photos to use for that area during mesh and texture generation?


bigben

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Re: Dealing with DOF
« Reply #5 on: February 17, 2015, 10:23:12 PM »
Mesh generation is done from the point cloud, so the photos will have no influence at that stage but the texture would probably be affected  as the image is projected onto the object based from the camera position

JohnyJoe

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Re: Dealing with DOF
« Reply #6 on: February 17, 2015, 10:37:23 PM »
Mesh generation is done from the point cloud, so the photos will have no influence at that stage but the texture would probably be affected  as the image is projected onto the object based from the camera position

Interesting...

1) So blurred (out of focus) areas are not generally a problem IF the parts of the model that are out of focus are IN focus (sharp) on other images of the subject with a good overlap? And this applies to dense point cloud generation and mesh generation?
Is this true...? So for dense point cloud generation and mesh generation there is NO need for focus-stacking in special programs?

2) But for texture generation out of focus areas even only in SOME photos, might be a problem, since photoscan can take this areas in those photos and make a texture out of them (not realizing, that the parts of model in this texture, might be blurred)? So focus stacking is usefull mainly only for texture generation step?

Do i get it right?

Mike25660

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Re: Dealing with DOF
« Reply #7 on: February 20, 2015, 06:07:36 PM »
Mesh generation is done from the point cloud, so the photos will have no influence at that stage but the texture would probably be affected  as the image is projected onto the object based from the camera position

2) But for texture generation out of focus areas even only in SOME photos, might be a problem, since photoscan can take this areas in those photos and make a texture out of them (not realizing, that the parts of model in this texture, might be blurred)? So focus stacking is usefull mainly only for texture generation step?

Do i get it right?

Would using the option of generating texture from a single photo help to minimize the effects of focus?


FoodMan

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Re: Dealing with DOF
« Reply #8 on: February 20, 2015, 07:34:53 PM »
well one can always mask the out of focus areas at texture step.. so PScan will discard these masked areas..

Alexey, would this help..?

f/

Alexey Pasumansky

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Re: Dealing with DOF
« Reply #9 on: February 20, 2015, 07:36:09 PM »
Masked areas are not used during any processing steps performed after masking (for Align Photos using masks is optional). So if the texture is built after blurred areas are masked, they will not be used.
Best regards,
Alexey Pasumansky,
Agisoft LLC

David Cockey

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Re: Dealing with DOF
« Reply #10 on: February 20, 2015, 09:14:43 PM »
"Sharpening" in Photoshop, etc does not increase the information in the photo. It just adjusts the contrast gradient locally to give the appearance of a sharper image.

My experience  is that PhotoScan is not very sensitive to slight blurring, and ignores badly blurred areas.

Mike25660

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Re: Dealing with DOF
« Reply #11 on: February 21, 2015, 08:55:48 AM »
Maybe another option for sharpening the final product is to exclude poorly focused images from the texture generation? I tried this on a small piece and it seemed to help a little but it could just be wishful thinking on my part. Does anyone have a good idea about how effective this might be?

Is there an optimum photo quality range, > 0.8, for instance, that generally gives sharp results?

I'm trying to create models of fairly small, 3-10 mm long, pieces. Using magnifying rings is helping to get as much of the subject as possible in a still frame, and this seem critical to processing. Getting uniform focusing is a definite challenge, so I'm still experimenting with the photography. So far my models are a little more noisy than I'd like to see.

FoodMan

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Re: Dealing with DOF
« Reply #12 on: February 21, 2015, 07:39:52 PM »
Thanks Alexey  8)

f/