PhotoShop – Automate Batch to remove content outside border

Updated Answer

Ok, I have done some work on this and can extract the map automatically using the script below which does more or less as I suggested below:

#!/bin/bash 
################################################################################
# File: extractMap
# Usage:
# extractMap survey.gif
# Result is in extracted/survey.gif
################################################################################
image="$1"
mkdir extracted 2> /dev/null

# Step1: Trim off border around edge of image
convert "$image" -shave 50x50 step1.gif

# Step 2: Squeeze image till 1 pixel wide x original height
convert step1.gif -scale 1x! -threshold 65533 step2.gif

# Step 3: Find longest black line
result=$(convert step2.gif txt: | awk -F"[,: ]*" '/black/&&!inblack{inblack++;start=$2}/white/&&inblack{inblack=0;l=$2-start;if(l>longest){longest=l;x=start;y=$2}}END{print x,y}')
read a b <<< $result

# Step 4: Crop top and bottom off
h=$(identify -format "%h" step1.gif)
c=$((h-b))
convert step1.gif -chop 0x$a -gravity south -chop 0x$c out.gif

# Step 5: Squeeze image till 1 pixel tall
convert out.gif -scale x1! -threshold 65533 step3.gif

# Step 6: Find longest black line
result=$(convert step3.gif txt: | awk -F"[,: ]*" '/black/&&!inblack{inblack++;start=$1}/white/&&inblack{inblack=0;l=$1-start;if(l>longest){longest=l;x=start;y=$1}}END{print x,y}')
read a b <<< $result

# Step 7: Crop left and right off
w=$(identify -format "%w" out.gif)
c=$((w-b))
convert out.gif -chop ${a}x0 -gravity east -chop ${c}x0 "extracted/$image"

You would save the script above in a file called extractMap, then run the following (just once) to make it executable

chmod +x extractMap

Now you can pass it the name of a survey like this and it will extract the map into a subdirectory called extracted followed by the original filename:

./extractMap survey.gif

The main steps are:

1. To remove the black border around the original image
2. To then queeze the image til1 1 pixel wide and original height
3. Find the longest black line in the squeezed image (that is the vertical edge of the map)
4. Crop the top and bottom off according to that line
5. Squeeze the image till 1 pixel tall
6. Find longest black line which is the horizontal edge of the map area
7. Crop left and right of map border and save in output directory

If you have a whole directory full of images, please back them up first then you can process the whole directory of thousands of files like this:

for f in *.gif; do ./extractMap "$f"; done

Orignal Answer

I am away without access to my computer for the weekend, so I can only suggest in general terms how to do it… will check back Sunday evening to see if anyone has developed the idea.

I would use ImageMagick which is available for Windows, Linux and OSX via commandline or with Perl, PHP, .NET and other bindings.

Then squeeze the image to a tall, 1 pixel wide image, using this command

convert inputimage.jpg -resize 1x! output.jpg

Now look at the image, and you will see a short solid line corresponding to the image title block at top left, then another short line corresponding to the longitudes and then a LONG solid line corresponding to the sides of the map. This is readily identifiable and gives you the top and bottom of the map.

Now squidge the image to 1 pixel high with this

convert inputimage.jpg -resize x1! output.jpg

and do it again to find the width of the map.

Then extract the map with

convert inputimage.jpg -crop XxY+M+N output.jpg

where X=map width, Y=map height, M=x offset to top left corner of map, N=y offset to top left corner of map.

You can change the output image name to txt:- and it will list the pixel colours as text so you can parse them easily.

Thinking a little more, it would be better to crop the top and bottom of the image off after finding the longest vertical line and BEFORE squidging the image down to 1 pixel high – this would mean the header at the top and key at the bottom would not interfere with determining the width of the map.