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by Wendi E. M. Scarth.


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Improve Scanned 
Images GIMP


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Improve Scanned Images Using Three Filters
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Improve Scanned images GIMP (GNU)
Improve Scanned images GIMP (GNU)

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This GIMP (GNU) tutorial demonstrates how to Improve Scanned Photographs using three filters. To work along, you are welcome to download the Scanned Illustration I am working with HereUnzip the file and open the image onto GIMP’s workspace.

Thank you Rob, for the illustration of Thomas.

Scan Note
When scanning photographs or text, set your scanner to 300 DPI.

Each image is unique, and therefore has different needs. With this in mind, when working with your image, it’s important to experiment with the settings outlined in this tutorial.

You can quickly Undo a step at any time by pressing Ctrl then Z. Alternatively, click a previous Undo History snapshot - Windows then Dockable Dialogues then click Undo History. In addition, to Zoom in (or Zoom out) of your image; from the top menu choose View then select a Zoom Tool from the subsequent drop-down list.

Improve Digital Photographs Using Four Filters

Launch GIMP & Organise Its Workspace & Palettes

Open your Scanned Image onto GIMP’s workspace - File then Open - Ctrl then O.

Ensure the Layers and the Undo History Palettes are visible, and then drag them into position over your workspace - (Windows then Dockable Dialogues - then click Layers and Undo History).

The Adjustment Curves Editor is possibly the best way to adjust the brightness of photographs: - it affords a sophisticated way of deciding what the impact value of a pixel should be adjusted to either by adjusting the combined RGB channels together, or by adjusting individual channels. Where brightness control simply adds a number to each pixel, and each channel without order; the Curves command can for example, increase or reduce the values of pixels in a non-linear fashion, and as a consequence, the middle values are adjusted leaving the extremes unaffected. This is how Curves can darken/lighten an image whilst leaving those colours close to solid black, and solid white, unaffected.

2/ The Cures Editor
Now, from the top menu, choose Colours and then choose Curves. And from the subsequent Curves dialogue box, create a S shaped Curve. To create an S Curve,
left-click to apply two Points along the diagonal line (curve adjustment line) - as illustrated below.

(Don’t click OK).

Now, left-click over the left-side Point - and then gently drag it slightly downwards - as illustrated below. Then release the left-mouse button.

(Don’t click OK).

Now, left-click over the right-side Point, and drag it slightly upwards - as illustrated below. Then release the left-side mouse button.

Then click OK to commit the Adjustment Curve edit. 

For personal results, take a little time to experiment with the Curves Editor.

Congratulations, you have adjusted your image’s curves.

3/ The Threshold Command (Improve Your Scanned Image’s Contrast)
From the top menu, choose Colours and then choose Threshold. And from the subsequent Threshold dialogue box, grab the Black Point tab, and drag it a little to the right - as illustrated below.

The Threshold Command transforms the Current Layer or the selection into a black and white image, where white pixels represent the pixels of the image whose Value is in the Threshold Range, and black pixels represent pixels with Value out of the Threshold Range. 
You can use it to enhance a black and white image (a scanned images and text for example), or to create Selection Masks.

Adjusting the Black Point improves your image’s contrast (black and white pixels) - as illustrated below.

For personal results, take a little time to experiment with the Threshold Command.

4/ Sharpening Filter
Now, from the top menu, choose Filters then choose Enhance and then choose Sharpen. And from the subsequent Sharpen dialogue box, experiment with the Sharpness setting, and then click OK.

Sharpen Images Tutorial

For personal results, take a little time to experiment with GIMPs Sharpening Filters.

Congratulations, your work is complete,
and it is ready to save - top menu, then File then Save As.

Important: Save
To preserve your original photograph, always choose Save As, as opposed to Save.

Final Notes
My three-step photo fix principle works well in most situations; however, for personal results, it’s important to experiment with the Tools, Filters and Commands that GIMP offers, and discover the best steps for your scanned image’s requirements. And don’t forget the importance of the Crop Tool: cropping away distracting elements can dramatically improve your photographs. (
Crop Tool Tutorial).

Wendi E. M. Scarth. 
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