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Design-based profile for pinhole vignetting correction?

Nov 3, 2010 9:28 AM

I have a pinhole camera which shoots (nominally) 6x12cm frames on 120 film, with a 40mm focal length.  Naturally it has significant vignetting, as the corner of the frame is almost twice as far from the pinhole as the center of the frame, making the corners about two stops down from the center.

 

Is it possible to hand-build a design-based lens profile for this to automatically correct for the vignetting?  How would I do that?

 
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  • Currently Being Moderated
    Nov 3, 2010 3:37 PM   in reply to Mark Sirota

    The design based lens profile as opposed to build from the checkerboard images?

     

    Yes, it is possible if you can create the lens design data interchange format as those used by the ALPC. ALPC can do the conversion for you to generate the lens profile. You can go to the ALPC Adobe Labs page. Under the Product Details page, there is a PDF doc http://download.macromedia.com/pub/labs/lensprofile_creator/lensprofil e_creator_cameramodel_dataconversion.pdf that describes the interchange format.

     

    -Simon

     
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    Nov 4, 2010 12:11 PM   in reply to Mark Sirota

    Mark,

     

    Check out this thread http://forums.adobe.com/thread/690985?tstart=60 that might help. There is a <stCamera:CameraRawProfile> tag in the lcp file that indicate whether it is for raw or non-raw images.You can hand edit it support your non-raw workflow case.By default, the design based profile is generated for raw images.

     

    -Simon

     
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    Nov 4, 2010 4:43 PM   in reply to Mark Sirota

    I thought it needs the focus distance info to be specified in the lens design data interchange file.

     

    -Simon

     
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  • Currently Being Moderated
    Nov 5, 2010 4:24 PM   in reply to Mark Sirota

    Hi Mark,

     

    Good to hear that you have figure it out yourself. Sorry I side tracked by work  items and did not get a chance to respond to you earlier.Normally,

    for designed based  profile, you don't need to specify the <stCamera:FocalLengthX> and <stCamera:FocalLengthY> info. It is not available because it does not  know the sensor pixel pitch ahead of time (it only has the lens info). So it only needs to specify <stCamera:FocalLength> in millimeters. But in your case, your image is from scanned films so you can compute <stCamera:FocalLengthX> and <stCamera:FocalLengthY> info ahead of time.  The <stCamera:FocalLengthX> and <stCamera:FocalLengthY> are defined as f/Dmax as documented, where f is the focal length (in your case 40mm) specified in the number of pixels. So you know the scanner resolution @2400ppi, so your f = 40 * 2400 / 25.4 = 3779.5275 pixels. With your Dmax = 11314.584 pixels, the <stCamera:FocalLengthX> and <stCamera:FocalLengthY> comes out at

    0.3340403. So you got it right. Congratulations!

     

    I'd like to see your image before and after the correction :-)

     

    -Simon

     
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  • Currently Being Moderated
    Nov 10, 2010 9:46 AM   in reply to Mark Sirota

    Very cool. Because those profiles does not contain metadata tags for the camera and lens, ALPD does not how to handle it so they do not show up.

     

    -Simon

     
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