Find midpoint of irregular shaped area

If you want to find the centre of gravity - which would normally be considered the midpoint of an irregular shape, you can do it in Photoshop although it is a little awkward.

1. Draw around your shape with the pen tool to create a shape and fill it with a solid color. Then turn off your image layer.

2. Use Select color range to make a selection of your color and in the histogram, expanded view, ensure Cache level is 1 (if not click the triangle at the top right of the histogram). Then read the number of pixels (in my case 4836668)

3. Calculate half that number of pixels - so for me 2418334

4. Add a white rectangle shape just above the irregular shape layer and position the edge approximately halfway down.

5. Press Ctrl+D to Deselect and select color range again

6.Read the number of pixels in the histogram - remember you must be at cache level 1 so click the warning triangle if not.

7. Move the white rectangle up/down and repeat steps 5 & 6 until you have as close as possible half the pixels as calculated in 3.

8. Drag a guide from the ruler an position it on the edge

9. Move the rectangle so it's vertical edge is across the shape and repeat steps 4-8

10. Your guides are in the centre of gravity so you can now turn off the shape layers and turn the image back on

Like I said - it is a bit awkward - but it does work.

I hope that helps

Dave