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I have a scan of an old anatomic atlas; it's grayscale and not really bright. I suppose it's a copy of an engraving. My question is: is it possible to remove this background relatively easy? Or magnet lasso will be the only option?

enter image description here

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Is this question for photostack? They are stacks about PSP. Is not related with anything about photography. –  Leandro May 23 '13 at 19:55
    
I'm awfully sorry if I did something wrong, but I saw questions about photoshop here. –  Amomum May 23 '13 at 19:56
    
Welcome to the GraphicDesign side. Are you trying to isolate the cartilage or are you trying to remove the dots which obviously are part of the cartilage as well? Isolation will be very easy, removing the dots from inside would be challenging but not too hard. –  Ryan May 23 '13 at 20:29
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@Leandro: thanks, I'll rtfm next time :) –  Amomum May 23 '13 at 20:53
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@Amomum that doesn't answer the question. Do you want the leg to look smooth or you want the leg to look like it does with the halftone? –  Ryan May 23 '13 at 20:55
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enter image description here

Seems pretty straightforward with Photoshop CS6. I used the dropper tool to select the general background and did cleanup with the quick selection tool.

Note:

If the selection of the background ends up breaking due to the "grid pattern", you can work around it, like I did, by duplicating the later and applying a blur filter to smooth it out, then applying the magic wand selection. Switch back to the other later and fine tune with the quick selection tool.

All told, it took about 5-10 minutes to do the selection and rough cleanup. Can probably do a better job if you spend more time and then apply some filters to improve the contrast of the image.

enter image description here

Some tweaks to bring out the details of the original.

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Old school "descreening" was achieved by taking an enlarged film slightly out of foucs and then reducing it. This can be done digitally by doubling or more the pixels count, blurring and then reducing back to original size. –  horatio May 23 '13 at 21:23
    
@horatio more or less what I did with the original. Something I picked up back in the day when I was scanning newspapers for reports and hated that "grid/screen" look. The modern tools makes it fairly straightforward. In the above, I used that to generate the mask, which I then applied to the scaled up original to retain as much of the original detail and contrast. Then applied some noise removal and unsharp mask to bring out the features in the second image. –  Wing Tang Wong May 23 '13 at 21:26
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@WingTangWong the author of the drawings is Cloquet, according to the caption :) –  Amomum May 23 '13 at 21:39
    
Awesome, thanks. Ah... a surgeon. of course. :) –  Wing Tang Wong May 23 '13 at 21:44
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Ah, great call on using the blur to get a selection and then going back to the original. Wish I had thought of that. –  AJ Henderson May 24 '13 at 3:03
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In Photoshop, the best tool for that job would be the Pen Tool, as it will create nice straight lines and curves. If you don't have the patience for that, the quick selection tools will do an ok job, and you can use Quick Mask to clean up the selection

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Try:

Increase the pixel count aggressively (e.g. ~1530px wide to 10,000px), apply a strong blur filter, and then reduce the image back to the original pixel count. This will get rid of (most of) the halftone dither.

Use the magic wand tool with a setting around 20-30% and "contiguous" enabled. Select the outer grey area, invert the selection and then apply this selection as a layer mask. Tweak the layer mask as needed.

Place a layer below the image and flood it with white.

Note that you can do the masking at the higher resolution and the imperfections will be lessened after reducing back to original size.

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Whenever there is a rasterized scan our automatic selection tools fail. I therefore remove the raster with a despeckle tool first. This will also considerably reduce the image size after compression.

We can then quickly adapt the image color levels as done here:

enter image description here

These are the three steps I had to take using Gimp 2.8:

  • Filters - Enhance - Despeckle: non adaptive, Radius 2
  • Colors - Levels: Black Point: 0 Gamma 0,5 White Point 165
  • Colors - Hue-Saturation: Saturation -100

This method will of course also remove the raster from the object but is is the fastest way I know of. Without fine tuning it could be done in less than a minute.

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Interesting filtering method. Also interesting how the look of the bones is likewise changed. Very cool. –  Wing Tang Wong May 24 '13 at 16:59
    
Yeah its best on many tiny objects or on scanned text documents with a rasterized background where selection tools fail. –  Takkat May 24 '13 at 17:39
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Here's my take on this:

IMAGE

I made this in GIMP, but the general steps should be similar in Photoshop:

  1. First, I used the Descreen plugin to remove the screen pattern. There's a similar plugin available for Photoshop. I left the settings at their default values (sensitivity = 72, selection growth = 16, middle preservation = 5), but unchecked the "despeckle" checkbox.

  2. Next, I used the Levels tool to make the background pure white and to darken the dark parts a little. I also used the middle slider to slightly darken the midtones for improved contrast.

  3. Then I cleaned up the remaining not-quite-white spots in the background by first selecting the background using the Magic Wand tool with threshold 0, then enlarging the selection by one pixel and shrinking it by the same amount, and filling the resulting selection by one pixel.

  4. Finally, just for a finishing touch, I decided to make the background transparent. (View the picture on a non-white background to see the effect!) To do that, I selected the background (including the gaps between the toes) again, enlarged the selection by two pixels and feathered it by one to put the selection boundary just inside the edge of the drawing, and then used Color to Alpha to replace white with transparency in the selected area. I did have to first tweak the selection manually at the tip of one toe, though, since there was a gap in the drawing's edge there.

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