Guide to image improving with GIMP 2
Guide to image improving with GIMP 2

Introduction

This guide helps you to align, crop and enhance bitmap images of any type - mostly ones with text in them.
The steps shown in this guide can also be used to prepare images for Optical Character Recognition systems or better print quality.

Status: WIP

Basic improvements

  1. Coarse rotation: if the image is upside down, align it roughly (90° steps):
    Image » Transform » Rotate …

  2. Coarse crop: if the image has unneeded areas:

    ⮱ Crop all unnecessary areas using the crop tool (less RAM & CPU usage):
    Shift + C » select area to keep » then crop with ENTER

  3. Fine rotation: if the image doesn't have lines to align with the grid:

    ⮱ Open the Layers - Dialog with Ctrl + L or through Windows » Dockable Dialogs » Layers and create a new layer:
    Mode: Normal
    Fill with: transparency
    Switches: ✖️ Visible

    ⮱ Press N to select the pencil:
    Brush: 1x1 (1. Pixel)
    Size: 1~20 (according to image resolution - you need to see the line)
    Everything else: default

    Now you can look for a horizontal & vertical position to draw your orientation lines…
    …if you want to align to text margins directly, you can also skip this step - not advised!

    You can activate the Grid trough View » Show Grid

    Select the Arbitrary Rotation - tool, make a coarse alignment and then adjust the image to the exact angle by manipulating the Angle - value (press TAB after changing the value to update the preview). Then apply the changes with Rotate.
    Image » Transform » Arbitrary Rotation…

  4. Fine crop: use the crop tool to select the final area of the image you want to preserve. Then press ENTER

  5. Resizing: if needed, resize your image to fit in it's final destination. To do so, select Image » Scale Image… and adjust it to your needs.
    You can also enlarge the image without resizing its contents:
    Image » Canvas size…

Optical enhancements (can be used for OCR & printing too)

  1. Image enhancements: now that we have the right orientation and size, the image needs to be enhanced. Depending on what kind of image we have and which medium it was captured with, different steps are needed to improve the image.
  • :

I created this guide from my own experiences. If you have something to add I'm really thankful to hear from you.

Documentation - Manuals - Guidelines - Instructions by NA0341 is licensed under CC BY-SA 4.0

Share Note for Obsidian 🌓