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Perspective Correction

Perspective distortion causes parallel lines appear to converge at a long distance. We all are aware of this illusion. Wider the lens, more acute is the distortion. While taking photograph of a tall building or structure from a short distance with a wide-angle lens, the building appears to be tilted. One way to correct this effect optically is to use a Tilt and Shift lens. These lenses can be shifted and tilted with respect to the focal plane to compensate this distortion. The problem is, they are quite costly J However, we can achieve similar correction digitally by using a simple technique in PhotoShop. Let me illustrate this on a photograph of a window, taken obliquely with a wide-angle lens. The distortion is very acute. After applying the technique the result is amazing!

Before

After

Technique step by step (for Photoshop 6.0)

  1. Load the photo to be edited. Make sure the photograph is in 8 bit mode. This Distortion tool only works in 8 bit mode. So convert from 16 bit to 8 bit is necessary.
  2. Enable the Grid line on screen by pressing Atl Ctrl ' or select View>Show>Grid from the menu

    This will turn on the Grid on the picture

  3. Select the entire image by pressing Ctrl A
  4. Select Distort Transformation by selecting Edit>Transfor>Distort from the menu

  5. Now stretch the distort marquee by dragging the handles (small rectangular boxes) at the corner. Visually align the tilted edges with the vertical and horizontal grid lines till you are satisfied with the correction. Remember, adjust both corner handles as well as the middle handle in turns in little increment and check the effects.

  6. Hit enter key or click the tick box to confirm your change. Voila! you have the perspective corrected image.