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Extracting people (onjects) from image

Posted on 2002-07-02
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Last Modified: 2010-04-06
Hi,

Suppose I have a bitmap image (BMP) and I want to extract some specific object from it (like a person) only, without the background, how do I do it? Is there any specific software that can do this (freeware/shareware)? If not, how can I do it through photoshop?
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Question by:hardeepbsingh
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weed earned 50 total points
ID: 7125208
Common question, not so easy answer. It TOTALLY depends on the object and the background. If the background is a solid color its easy but most arent. You will need to make a series of selections with your magic wand tool with various tolerance settings in any of your 4 channels in order to isolate the foreground object. There is no hard and fast way to do it. No settings work well for all pictures so you will have to experiment with tolerance and channels to find the best method for your image. I can tell you to find a channel with a high contrast between the foreground and background to make your selections easier. Dont forget to switch back to the composite before deleting the background.

You can also try using masks but again, every image is different. Paint out the background in a mask and turn it into a selection, invert the selection, and copy the foreground.

All this applies to Photoshop. There arent any programs that you can just push a button and have it work.
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by:zombeen
ID: 7126063
in photoshop, the best thing to do wud be to use the pen tool , which is just like drwing , and since u might not be an "expert" in it , you can always edit/add/delete any number of nodes as long as u r fully satisfied . i think this wud be best for u as well

zombeen
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by:hardeepbsingh
ID: 7126070
pen tool? does that mean that I have to draw out the boundary of the object? please let me know some details since i am neither a designer, nor very good at drawing.

The question is still open for other suggestions.
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by:zombeen
ID: 7126346
yes.. u wud have to draw the outline... but as i said , u need not be a great atist to make a really freat cut out , as you can always modify the drawing pts (nodes) as many times as u want.. for more info.. i suggest u read more abt pen tool from the photoshp help
as its gonna be diff for me to explain how it works from here.  though i am always there for more help whenever u get stuck

zombeen
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by:weed
ID: 7127185
The pen tool is really only effective for large smooth sided objects. If there's alot of small detail then its simply not practical. It will also leave a fringe if youre not right on the edge of the pixels you want to grab. Its much more effective to make a smart selection.
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by:hardeepbsingh
ID: 7128942
I tried smart selection but it always gets a part of the background also, although I kept adding/removing parts from the selection. I have not yet tried the pen tool but I think the foto has too much detail and would be difficult. I am surprised how it is done so well professionally.
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by:weed
ID: 7129127
If youre picking up background, look for a channel that has a higher contrast between foreground and background, and adjust your tolerance.
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by:hardeepbsingh
ID: 7131163
1. Do the following steps mean anything to you guys:
      Step 1: Read Image
      Step 2: Maximize Contrast
      Step 3: Subtract Images
      Step 4: Convert Objects of Interest
      Step 5: Detect Intensity Valleys
      Step 6: Watershed Segmentation
      Step 7: Extract Features from Label Matrix

2. Where do I select a channel and tolerance?
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by:weed
ID: 7131171
Channels are in your channels palette, tolerance is set in your options palette. If youre unfamiliar with either of those or what they do you should become familiar with them before going any farther. They are both explained in your manual.
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by:HJohnson
ID: 7163524
Just bring the bitmap into windows PAINT, use the freeform select tool and trace out the picture you want.  Then save the bitmap to another file or just copy the freeform bitmap.  You can then paste it in anywhere you want.
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by:ninjadeathtouch
ID: 7184971
Another solution is to look for neural network software that does edge detection.  There are plenty of shareware programs that do stuff like this - loads of uni projects revolve around developing these (I did a few!) - and it's not half as scary as it sounds.

Get hold of a copy of Neural C - if you can program in C, and do it yourself (look up the Multi-layered perceptron for a starter) - or if you can't program then look for some stuff that other people have done.

This will allow you to find the edges of the image - all you need to do is train it with the background image - then show a few with the people on top - then it will have no trouble recognising similar images regardless of small changes in the background or people.

I know it's not an answer - it's a least 6 years since I did this - but I know you can do it this way and there used to be quite a lot of shareware to demonstrate this - there must be loads now...

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