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I am using ArcGIS 10.2 to show a facility's size and position in a project area. I was not given any shape files or survey files of the area. I only have a deed (.pdf) with a B&W sketch of what the area of the project is. I created a JPEG from the deed image and have used the georeferencing tool to lay it into the correct position in my map as a raster. I would like to show only the black portions of the jpeg and filter out the white background. Is there a way to do this? enter image description here

Here is what I have right now. I would like to get rid of the white, completely leaving only the text and black lines. I realize that I could just trace the image--creating a new feature--but for my purposes the preservation of the original writing and lines from the deed is necessary.

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Yes, there is a way to do that. In the symbology palette for the overlay raster, you can select the Display Background Value (R, G, B) _ _ _ as ___ option (see screenshot for a raster I have doing the same thing with a white background. Assuming your background image is truly all white, your values will also be 255, 255, 255 in the boxes. Make sure to select the "no fill" patch as your color in the "as __" box.

The options in the red box are what you want here

  • Thank you nicksan. This method worked but left a lot of white pixels around the image. After I used your method to get rid of most of the white, I used the image analysis window to work the pixels out of the image as best I could with the different filters available there. – gyoung1986 Jan 6 '15 at 19:44
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You can block out the "white" using a Mask function, through the image analysis window. Change NoData Interpretation to "All", and add values 0 (minimum) and 250 (maximum) to all bands in your raster. As your image may contain "near white" values, you may want to lower the masking threshold to, say, 245. The "white" values will also depend on the pixel depth of your raster, so you may have to identify some white pixels beforehand.

enter image description here enter image description here enter image description here

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The answer by nicksan is good, though if your pdf was not be a perfectly-white background, you might have better luck removing it in image editing software rather than ArcGIS. After doing that, georeference the new image.

There are a number of ways to do this. If you have access to Photoshop, you could try the magic wand tool. Other image editing software (including the free Paint.NET) has similar functionality.

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    I don't agree with the notion of removing the image from ArcGIS and then Georeferencing it again. You'll have a hell of a time getting it as accurate as it was originally. There are plenty of options for filtering out and even removing colors that do not require exporting the image to a a graphics editing program only to have to bring it back in. – MrBubbles Jan 6 '15 at 19:59
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    I certainly see your point, @MrBubbles, and I agree that in general it's simpler not to use an external program. I just figured I'd give another option. I disagree with your comment that it would be hard to get it as accurate as it was originally. Georeferencing is not particularly difficult, and there is no reason the second try won't be as accurate as the first. Who's to say the first try was particularly accurate? The second may be even better. :) – susie derkins Jan 6 '15 at 22:04
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    At a minimum, repeating the georeferencing is a time-waster. But by taking some care with the image processing software (so as not to change the actual image extent or format), it should be possible to redo the original georeferencing with one easy mouse click, merely by saving the "link file" the first time around and using that to georeference the modified image. But ArcGIS itself has more than adequate image-manipulation capabilities to handle this entire task! – whuber Jan 6 '15 at 22:31
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    ArcGIS Is a GIS tool not an image manipulation tool. This answer is totally acceptable. You CAN use GIS if it works, but you may need to use an image manimpulation software such as ImageMagick/Photoshop/Gimp/Irfanview to do a better job. You can also automate these tasks, and depending on how you have it georeferenced, you wouldn't have to georeference again. – JasonT Jan 7 '15 at 0:20
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I do this a lot with historic maps, and began by using @nicksan's method, but had the same issues the OP mentioned. I haven't used the mask method (will try soon) but here's what I do now, if you can deal with not having the red and blue in your overlay:

  1. Make sure you have Updated Georeferencing in the georeferencing toolbar and then remove the layer from the TOC
  2. Make a backup copy of the image using ArcCatalog
  3. In GIMP or Photoshop change the image mode to grayscale (and save it)
  4. In ArcMap, add the image back in and change the symbology to Unique Values (this is not an option with an RGB image)
  5. Set the color ramp to black to white (or white to black) and click Apply
  6. Now just remove as many of the white/gray values as you like

This is also nice because you can choose any color ramp and display multiple line drawings on top of each other.

Some other notes:

I would recommend viewing the image where it exists in windows explorer and checking out the extra files that are associated with it. This depends on the format and the version of ArcMap you're using, but once an image is georeferenced, there are always auxiliary files that accompany it. The jgw in this case holds the spatial extent, and the .xml holds the spatial reference and georeferencing info, etc.

This means that in your new grayscale version of the image, all the georeferencing info will be retained and it should be no problem.

HOWEVER If your image has pyramids, you'll have to delete that file, which is often a .ovr or .rrd. The old pyramids will show the old image at small scales.

Basically, it's worth figuring out a good way to do this if you'll have to do it again, because removing the white pixels is worth the trouble.

  • That sounds like a great method. I will keep that in mind next time I have to use georeferenced overlays. – gyoung1986 Jan 8 '15 at 5:04

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