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08-01-2008, 09:25 PM   #1
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How do YOU de-fish?

I love the look and FOV of my 10-17 FE but I'd like to play around with de-fishing sometime. I've searched and searched, and seen much talk of defishing with this or that software most of which I've downloaded and played with, but failed to be satisfied with my results.

It seems that the most recommended program would be PTLens, and other programs which use the PTLens database, and it seems to me that the PTLens database doesn't include the Pentax DA 10-17 FE, which is the lens in question for me.

So if you've succeeded in de-fishing your shots from this lens, would you mind sharing your secrets with me? (or at least pointing me toward a tutorial out there somewhere.)

Thanks.

08-02-2008, 04:16 AM   #2
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i don't know if it would work but in photoshop. Filter->Distort->Lens correction->remove distortion
08-02-2008, 04:26 AM   #3
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Sometimes I use the lens correction feature in CS3, and sometimes I use the PTLens plugin.
08-02-2008, 07:52 AM   #4
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QuoteOriginally posted by heliphoto Quote

It seems that the most recommended program would be PTLens, and other programs which use the PTLens database, and it seems to me that the PTLens database doesn't include the Pentax DA 10-17 FE, which is the lens in question for me.

So if you've succeeded in de-fishing your shots from this lens, would you mind sharing your secrets with me? (or at least pointing me toward a tutorial out there somewhere.)

Thanks.
Well, I don't have the 10-17FE, and I don't use PTLens, but since the package I do use

( hugin - Panorama photo stitcher )

uses the same lens distortion model, this might be applicable to your problem (or you could just use hugin )

Here's a de-fished image (the source image is at the head of the fisheye fever thread)


(click here for larger versions of this image)


Four parameters are most important:
The lens type (fisheye)
The horizontal field of view of the input image; For a sigma 8mm this is 185 degrees; for a pentax 10-17 I'd expect this to be about 140 degrees at 10mm and about 82 degrees at 17mm
The projection type of the output image (rectilinear)
The horizontal and field of view of the output image (choose anything less than the HFOV of the input; in the image above it's about 120 degrees)

Hugin (I'm not sure about PTLens) also allows you to specify the pitch (up or down) of the input image; this is lets you do de-fishing and perspective correction in a single pass.

Using the hugin GUI:

load a single image
specify the HFOV and lens type (fisheye) of the lens,
go to the sticher tab
set projection to rectilinear
set desired horizontal and vertical FOV
click on "calculate optimal image size"; you might want to reduce this
for output:
uncheck "blended panorama"
check "remapped images"
Click "stitch now"

The easy way once you set it up:

I found it more useful to use a batch file that calls dcraw to do the RAW->TIFF conversion, and then calls nona (the hugin remapper) directly to generate a de-fished TIFF image. Then I go into photoshop or GIMP to tweak the levels and make the JPEG.

I've attached an example; a bunch of stuff (-C parameters to dcraw, parameters described above, paths to dcraw.exe and nona.exe) would have to be changed for your situation

Attached Files
File Type: txt sigma8_rectilinear_1600.bat.txt (1.0 KB, 318 views)

Last edited by troyz; 08-02-2008 at 08:05 AM.
08-02-2008, 08:23 AM   #5
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QuoteOriginally posted by heliphoto Quote
I love the look and FOV of my 10-17 FE but I'd like to play around with de-fishing sometime. I've searched and searched, and seen much talk of defishing with this or that software most of which I've downloaded and played with, but failed to be satisfied with my results.

It seems that the most recommended program would be PTLens, and other programs which use the PTLens database, and it seems to me that the PTLens database doesn't include the Pentax DA 10-17 FE, which is the lens in question for me.

So if you've succeeded in de-fishing your shots from this lens, would you mind sharing your secrets with me? (or at least pointing me toward a tutorial out there somewhere.)

Thanks.
PT Lens doesn't include fisheye correction in the later versions, as it is impossible to decide whether the user wishes to have a wider view or just retain the same aspect ratio, thereby loosing some of the wider FOV.

Here is an example of what I mean:

The original image



Defished with PT Lens (distortion slider set to 130)



Cropped in Photoshop (top & bottom only, to remove black areas)



Cropped in PTLens with Crop slider set to 21 (preserving ratio).



I hope this is helpful.

Last edited by Richard Day; 08-02-2008 at 08:28 AM. Reason: added PTLens settings
08-02-2008, 08:45 AM   #6
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QuoteOriginally posted by troyz Quote
Well, I don't have the 10-17FE, and I don't use PTLens, but since the package I do use

( hugin - Panorama photo stitcher )

uses the same lens distortion model, this might be applicable to your problem (or you could just use hugin )

Here's a de-fished image (the source image is at the head of the fisheye fever thread)


(click here for larger versions of this image)
I've never used Panorama photo stitcher, but it looks like that de-fishing process introduced some pretty severe distortion and blur. You shouldn't have to sacrifice huge amounts of detail just to de-fish an image.

I took the liberty of using your original fisheye photo from your previous post for purposes of comparison. I hope you don't mind. I could have been more agressive with the de-fishing, but I didn't think it was needed. Here is what the same image looks like after being de-fished with PTLens:
Attached Images
 
08-02-2008, 09:01 AM   #7
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How do I de-fish?

I've got this special fork.



(Sorry, couldn't resist.)
08-02-2008, 10:23 AM   #8
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QuoteOriginally posted by JJJPhoto Quote
I've never used Panorama photo stitcher, but it looks like that de-fishing process introduced some pretty severe distortion and blur. You shouldn't have to sacrifice huge amounts of detail just to de-fish an image.

I took the liberty of using your original fisheye photo from your previous post for purposes of comparison. I hope you don't mind. I could have been more agressive with the de-fishing, but I didn't think it was needed. Here is what the same image looks like after being de-fished with PTLens:
Thanks! I get a similar result geometrically (with better image quality because I have the 14 megapixel source image) by using hugin/nona with a input HFOV setting of 140 degrees instead of 185 degrees.

The image you show isn't rectilinear (straight lines in the scene are no longer forced to become straight in the image; see the pattern of bricks in the foreground of the each de-fished image) but has better image quality in the corners and is better aestheically.

You bring up a good point: rectilinear projection often isn't the best way to deal with distracting elements in a fisheye image. I can think of three alternatives:

-- Defish less (have the software treat the image as if it was created with a fisheye lens with a greater focal length)

-- Crop to remove dark corners or distracting objects

-- Do a cylindrical projection (or Mercator or Miller, etc); this straightens vertical lines but doesn't affect image quality as severely (and produces a unique kind-of-fishy look)

Good composition is the best solution -- however, I'm finding this to be very challenging with the circular fisheye

08-02-2008, 11:14 AM   #9
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QuoteOriginally posted by heliphoto Quote
I love the look and FOV of my 10-17 FE but I'd like to play around with de-fishing sometime. I've searched and searched, and seen much talk of defishing with this or that software most of which I've downloaded and played with, but failed to be satisfied with my results.


This was from Zen 16mm with dslr at around 85 degree of FoV. I use an ancient version of PSP version 8. I think even version 12 is cheap. All you need is to set the FoV and in this case it is reduced from 85 to 74 degree of FoV . I have to say it is not as wide as the wider end of your lens















Daniel
08-02-2008, 11:49 AM   #10
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QuoteOriginally posted by rparmar Quote
I've got this special fork.



(Sorry, couldn't resist.)
I needed that. Very funny!!
08-05-2008, 04:59 AM   #11
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Original Poster
Thanks everyone for your answers. I've been super-busy lately, so I haven't had a chance to look into any fishyness or try out your suggestions, but I will.

rparmar, didja get your fork from B&H or somewhere like that?, or do those ebay ones work just fine? I have a Mac, so do I need a "resource fork?"
08-05-2008, 05:28 AM   #12
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QuoteOriginally posted by heliphoto Quote
I have a Mac, so do I need a "resource fork?"
Ouch!
08-05-2008, 08:58 AM   #13
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I'd like to second hugin, I realize this is my second post about hugin, but I'm just figuring it out right now, and keep being supprised by what it can do and how well it does it, especially for being free.
08-05-2008, 03:36 PM   #14
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Fisheye hemi is another one.... Image Trends - Fisheye-Hemi Plug-In - Corrects Fisheye Lens Distortion and retains Image Content Details
08-05-2008, 04:51 PM   #15
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Here's one I took with the Zenitar 16 fisheye that looks good defished with hugin/nona


pbase link

A non-defished image for comparison
link to source image

While de-fishing this image I discovered that hugin doesn't antialias well during downscaling; to get an 800px wide image it's better to de-fish to 1600px (or larger) and then downscale in GIMP than to defish directly to an 800px wide image.

De-fishing batch script attached.
Attached Files
File Type: txt zenitar_rectilinear.bat.txt (1,014 Bytes, 305 views)

Last edited by troyz; 08-08-2008 at 11:49 PM. Reason: gallery cleanup
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