Photoshop: clean up newsprint background?
February 19, 2007 9:49 PM   Subscribe

How do you use Photoshop to clean up the "newsprint-like" background noise behind a text graph?

I'm converting scanned overhead transparencies to jpgs. In some cases, the transparencies carry shading from a second side, like newsprint. See example here

I've tried selecting sections and replacing or filling, but it tends to infringe on/degrade the print/text quality. I need a nice dark print against a clean background. This should be easy, shouldn't it?

posted by rexruff to Computers & Internet (11 answers total) 3 users marked this as a favorite
Use Ctrl+ L and play around with the three arrow drag bars. I usually pull the right one a bit towards the centre, the left one a bit towards centre, and the centre one a bit towards the right, if that makes sense. You can also fiddle with Ctrl + M to get a similar effect.
posted by Phire at 9:56 PM on February 19, 2007 [1 favorite]

Comme ├ža

(apologies for self-link? does this count?)
posted by Phire at 9:59 PM on February 19, 2007

I use the magic eraser tool as well as Auto Levels to set the white point to the background. This removes background noise from scanning letterhead, textbooks, etc.
posted by Blazecock Pileon at 10:01 PM on February 19, 2007

Phire has it. The rightmost arrow in the levels window indicates, of the image data, what point in the grayscale will be 100% white. By moving the slider towards the middle, you are forcing those slightly darker show-throughs to become 100% white, giving you a nice clean result.

You don't mention if you're doing any more scanning, but in the future if scanning a light page with black text/images on back, it's best to lay a black piece of paper behind it. It makes the reverse side a smooth tone rather than blotches of black that show through when using the white background you usually find on scanner lids.
posted by lovejones at 10:37 PM on February 19, 2007 [1 favorite]

As with all things Photoshop, there are several ways to accomplish what you're looking to do here.

As mentioned, Levels will work just fine, as will Image > Adjustments > Brightness/Contrast (this method will also bump up your blacks as it reduces the bleed-throughs).

Lastly, for a quick and dirty solution you could duplicate the image on a new layer and "overlay" it. Results are virtually identical to either if the above methods.
posted by triptychrecords at 11:30 PM on February 19, 2007

I've done a lot of this.

Apart from the suggestions above, you should also use the Unsharp Mask to put some detail back to the text and graphics.

The Unsharp Mask adds contrast to the edge pixels which takes away any erroneous artifacts leftover from the scanning and the resultant level adjustments - rendering them easier to read.

Filter/Sharpen/Unsharp Mask - (leave threshold at 0, radius 1 pixel and then starting at 50%, play around with the amount slider, and make sure you check the preview checkbox, so you can monitor the results).
posted by strawberryviagra at 5:06 AM on February 20, 2007

comme ca (aussi)
posted by strawberryviagra at 5:16 AM on February 20, 2007

After adjusting the levels as described above, duplicate the layer and the mode of the now topmost duplicate layer to 'multiply' to increase the weight of the darks.
posted by drinkspiller at 6:08 AM on February 20, 2007

As others have said, create adjustment levels for Curves and/or Levels to get the whites purer and the blacks bolder.

If it looks cleaner but still contains a few artifacts and bits of noise, try a noise reduction plugin like this one. You can get decent results with "Advanced -> Remove only half of wekar noise"
posted by deern the headlice at 6:41 AM on February 20, 2007

Another approach is to place a black piece of paper behind the page your scanning.
posted by doctor_negative at 7:18 AM on February 20, 2007

so ... how'd you go??
posted by strawberryviagra at 6:48 AM on February 21, 2007

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