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Photoshop

Tutorial

Tutorial #8

Perspective cropping - to cure converging verticals

You may have noticed that when you need to tilt your camera upwards or downwards to take a shot (for example, when taking a photograph of a tall building) that the vertical lines in the shot seem to converge. This can give a strange effect to the image; a tall building would appear to be falling backwards, for example.

There are specialised (and expensive) lenses that can eliminate this effect but this tutorial is based on Photoshop (CS and above) and uses the 'perspective crop' function to set an independent crop angle on each side of the image.

Here is a photograph of an old blast furnace. As you can see the building and the chimney appear to be leaning backwards:

Open the photograph in Photoshop, choose the crop tool and 'click-and-drag' to select the entire image

Make sure the 'perspective' box is checked and then 'click and hold' on the top left-hand selection box. Drag the selection box towards the centre of the top-edge of the image until the left-hand of the selection is parallel with the edge of the building. Make sure that the selection box remains at the top of the image otherwise you will crop off some of the top as well.

Repeat the 'click-and-drag' operation on the opposite top-corner of the selection, dragging it inwards until the side of the selection is parallel with the right-hand side of the building.

When you are happy with the entire selection, click the 'big tick' to finalise the crop.

The finalised picture will now display. Notice how the top section of the image has been 'stretched' to fit and the sides of the building are now parallel and not converging.

 

 

Roll mouse over image to see original version

 

This technique doesn't only have to be used with buildings - it can be used on any image where the sides of the view would be improved if they were parallel.

In the next tutorial we will look at a pet hate of mine - wonky horizons - and how to rectify them.

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