HELP! How do I fix this distortion?

Discussion in 'Retouching and Post Processing' started by cotdt, Jul 19, 2007.

  1. cotdt

    cotdt

    Jul 14, 2007
    Bay Area, USA
    HELP! I desperately need the lines to be straighter. My 18-70DX kit lens has a lot of barrel distortion at 18mm, which is the focal length I used to take this image. How do I correct this distortion? There is also some vignetting that I want to correct. I wish that they made perfect lenses. This is my brother btw.

    [​IMG]

    in case you're wondering, he is playing his pocket piano.
     
    Last edited by a moderator: Jul 19, 2007
  2. Phil,

    It might be helpful if you'd tell the forum what post procession program you use.
     
  3. cotdt

    cotdt

    Jul 14, 2007
    Bay Area, USA
    I use Photoshop CS3.
     
  4. Thanks. Now someone familiar with CS3 can respond to help you.
     
  5. cknight

    cknight

    663
    May 2, 2005
    Madison, AL
    Go to Filter->Distort->Lens Correction.

    This filter will allow you to correct for the up/down or left/right tilt of a lens, which causes the building to get "bigger" on the top. It looks like you had the lens pointed down.
    It can also correct for pincushion/barrel distortion.
    It has its limits but I've found it useful.

    I'm using CS2, so it may be in a different spot, but the filter should be there.

    Hope this helps.
     
  6. Another way to do this is with a perspective crop.
     
  7. ... and if the above techniques don't quite do the job, you may need to Warp the corners a little (Edit - Transform - Warp)
     
  8. RFCGRAPHICS

    RFCGRAPHICS

    Apr 30, 2005
    check out this photoshop plugin ...PTlens

    http://epaperpress.com/ptlens/index.html

    It is like DXO but much cheaper. They have many nikkor lenses in their database to correct for the distorations you are experiencing.


    You can download a 10 usage demo to try out

    I ran your image with ptlens in CS3 with the nikkor 18-70 database and got this result

    [​IMG]
     
  9. cotdt

    cotdt

    Jul 14, 2007
    Bay Area, USA
    Very nice! Thank you! I will do that!
     
  10. IMHO, the easiest and fasted way, with any Photoshop version, is:

    1) select the image with CTRL-A
    2) click on EDIT > TRANSFORM > PERSPECTIVE
    3clich on the little square at the bottom left (or right) corner, drag it further left (or right), then click on the center little square -at the bottom- and gently slide it left or right, until bothe sides of the images look vertical !
    3) hit RETURN
    ...if fine-tuning is needed, start again at #1 !

    original.

    Hope this helps ?

    BTW, you're LUCKY (the lens you used is of good quality), because this image doesn't have ANY "barrel" nor "pin-cushion" distortion... if it was the case, it would take slightly longer to make it straight !

    Cheers,
    J-P.
     
    Last edited by a moderator: Jul 20, 2007
  11. One more tweak to JP's version....

    When I do this process or any perspective crop (depending on the situation) I add a last minute tweak. I take the main subject of the image and check it's height/width, as compared to the orig and/or real life. I don't know real life in this situation, but when you do a perspective adjustment the size of the head gets shorter making it look a bit wider (or fat). So (in this case) I'd take a top layer that's been adjusted for perspective and stretch it a bit to correct the face just a touch.

    I think JPs got one of the best (easiest too) ways to make a shot right and adjust it... I just add a final tweak to the image to make the face look the way it did in the orig shot.

    Here's my adjustment with the final tweak added. A head without the final tweak is next to it so you can compare.

    [​IMG]

     
  12. cotdt

    cotdt

    Jul 14, 2007
    Bay Area, USA
    Very important technique I have learned today. The head floating in space scared me for a moment, though :)
     
  13. Great idea ! I never thought of correcting -on people mainly- the distortion induced by changing the perspective :329:...

    That's one thing i will have to check and cure from now on...

    Thank you "Bandnuts" !!!

    Cheers,
    J-P.
     
  14. Bob Coutant

    Bob Coutant Moderator Moderator

    May 17, 2005
    Pleasantville Ohio
    Bandnuts/J_P

    To see, and correct, the distortion caused by perspective warp, I use a technique due to Winfried Schwolgin. [I use Picture Window Pro, so the process may be slightly different in Photoshop.] I start by painting a red circle approximately in the center of the image; leave the paint tool active; and make the perspective warp adjustment. Any distortion is then obvious as a distortion of the circle, and I tweak the adjustment to make the circle round. [It frequently is a camera angle problem.] Finally, undo the red circle and close the paint tool.
     
  15. Bob, that's WAY TOO EASY!!! Thank you for sharing (just tired it in PS and it's a snap by linking a circle layer to the adjustment layer). That's a super fast way to put things back on track and even more important if you don't know what the orig is suppose to look like.

    I took my two headed monster photo and put a third head on it using this process. So the heads are now "perspective" (one done with perspective only adjustment) and "guesswork" (one done with the ol' eye ball the head process) and "calculated" (one done using the circle layer you mention). The calculated one looks very natural and has to be the best way to make a final tweak.

    [​IMG]
     
  16. Bob Coutant

    Bob Coutant Moderator Moderator

    May 17, 2005
    Pleasantville Ohio
    Kap...
    Glad you could adapt it to PS so easily. We owe Winfried a vote of thanks for this one.
     
  17. And you for bringing it to our attention. I have been doing this by guesswork up to now. Thanks.
     
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