How to stitch photo the hard way?

Discussion in 'Photoshop Tutorials' started by david, Sep 22, 2009.

  1. david

    david Guest

    I have a photo larger than my scanner so I had to scan it as two separate
    section with some overlapping.

    The two sections are about 4000 x 3000 each.

    Now I want to stitch them together. What I do is load each section into a
    layer in photoshop and do a rough alignment. Now in order to align them
    perfectly, I zoom in to pixel level at one side of the overlapped area, make
    one layer 50% transparent and nudge until the pixels line up.

    Then I zoom in to the other side of the overlapped area. Often, I need to
    rotate one of the layer to line up everything. Ideally I would put the
    center of rotation on the previously lined up area, and then drag the
    rotation handle to line up the current side. But at the pixel level, the
    rotation handle is not visible. If I zoom out until I can see the rotation
    handle, I can no longer see enough detail to line up the two layers with
    pixel accuracy.

    How do you get around this problem?

    I know there are stitching function in newer photoshop and standalone
    stitching software. But just for the challenge, how can I do this the way I
    david, Sep 22, 2009
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  2. david

    mike Guest

    The following works for me on PS7.0 (which doesn't have fancy alignment
    software) and assumes the two image halves overlap a little, and that
    they are within a few degrees of rotational alignment.

    1) Place them as two layers and align them approximately horizontally
    and vertically by eye (without rotating!!!).

    2) Now zoom in (to pixel view) to one side of the image (I am assuming
    the images are upper and lower halves) at a point where the overlap
    occurs and, assuming you have sufficient pixel contrast to do so, nudge
    until you have the pixels as close to spot on at that side. You can use
    transparency or whatever to help here.

    3) Now zoom out and select one of the layers and hit Transform Rotate.
    Before doing any rotation, drag the rotation centre point locator to the
    approximate point where the pixels have been overlapped correctly (it is
    the circle with the cross and dot in the centre - looks a bit like a
    telescopic gun-sight). Zoom in using Ctrl + and the side sliders to
    position the rotation point accurately on the exact point where you
    achieved the pixel match.

    4) Now use Ctrl - and the sliders and Ctrl + to get to the opposite side
    of the image (at pixel view) where there is a visable 'wedge' where the
    pixels don't match due to rotational inaccuracy. You can enter an angle
    into the 'Control bar' at the top (the one that becomes visible when you
    enter Transform - Rotate) - it is the box next to the little triangle
    5th from the left or 3rd from the right. Start by making 1-2 degree
    adjustments, and then by triual and error get down to tenth of a degree
    (or less) till you have a good pixel match on this side.

    5) Ctrl - out and check that you matched the pixels and not something
    else - then accept the change. Bring the layers up to full opacity and
    if you have sufficient overlap fade a mask in on the bottom edge of the
    top layer. Merge layers etc, and you are done.

    As long as the images are top the same scale, you should be able to get
    near perfect match by tis technique. If they are out of scale, you can
    add a scaling step the same way, although the pixels get a bit muddy and
    it is a little more trial and error.

    mike, Sep 22, 2009
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  3. david

    Kingdom Guest

    Try using the "DIFFERENCE" screen mode (drop down in layers palete) I find
    this invaluable when trying to line up pixel perfect joins

    see Matching Oversized Scans
    Kingdom, Sep 29, 2009
  4. david

    Joe Guest

    That seems to be one of the easier way, and the OP wants to HARD WAY. My
    guess would be doing it with the eyes CLOSED. Or hands behind ones back?
    Joe, Sep 29, 2009
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