User:Hellerick/How to calculate map area in Photoshop

(For Photoshop CS2)


 * 1) Select the area to be measured with Magic Wand Tool (W) (make sure that the Anti-alias option is switched off). (Note: the selected area shouldn't be white; fill it (Shift+F5) with another color if it is.)
 * 2) Copy the selected area (Ctrl+C).
 * 3) Create new image (Ctrl+N). In the dialog window make sure that Preset is switched to "Clipboard", the Color Mode is "RGB Color", and the Background Contents is "White". Remember the WIDTH and HEIGHT values.
 * 4) Paste (Ctrl+V) the area to be measured into the new document window.
 * 5) Choose Image > Adjustment > Threshold, and shift the lever into the rightmost position (Threshold level 255). What you see now has to be the area to be measured in black upon white background.
 * 6) Choose Layer > Flatten image.
 * 7) Invert the picture (Ctrl+I).
 * 8) Choose Filter > Blur > Average. Now all the picture has to become solid gray.
 * 9) Click any pixel of the picture with the Eyedropper Tool (I). Look at the Color window (F6) (switch it to RGB mode if necessary), all the three values (R, G, B) have to be the same. This value is the FACTOR, remember it.
 * 10) The formula is AREA = WIDTH × HEIGHT × FACTOR / 255. The accuracity is ± WIDTH × HEIGHT / 510, i.e. about ± 0.2% of the rectangle area. The units of the area are the same you used for the width and height.

Sounds too difficult, but when you're skillful enough the process doesn't take more than 20 seconds. — Hellerick 15:53, 9 August 2009 (UTC)