Editing Images


Editing images simply means changing the color/channel values of the pixels that make up the image and/or changing the size of the image. It's simple to say this, but there are numerous methods for doing so:


·      Creating new images from drawings or other sources.

·      Cutting, Copying and Pasting into the image.

·      Drawing into the image "free hand" using image editing tools

·      Using the Transform toolbar to change many pixels at once throughout the drawing.

·      Using commands from the Image Menu such as resize to change the size or otherwise edit the image.

·      Changing the image by projecting/georeferencing it.

·      Altering images with scripts or other tools.

·      Using Edit - Save/Load Mask/Channel to alter the image by channel (used to compose RGB images from multiple grayscale images).

·      Edit the image using update queries that operate on the image's virtual table to directly change the colors of pixels or other characteristics. See the Virtual Tables for Images and Surfaces topic as well as the Queries and Images or Surfaces topic.

·      Use commands


Not all editing effects will work with all types of images. Some effects will require RGB or RGBa images to function, since they require a continuous selection of many colors. Compressed images may not be edited.


Resizing Images


To resize an image by cutting away pixels or by adding pixels at the margin, use the Transform toolbar Crop , Crop Margin and Add Margin operators.


Changing the size of the image while retaining the visual appearance by inflating pixels or compressing them into fewer pixels requires resampling the image. Use the Image - Resize command to change the size of the image in such cases. This dialog allows a choice of methods to resample the image into a larger or smaller number of pixels.


Cropping Images


The Crop Margin on the transform toolbar for images crops the image down by the given number of pixels at the margin. The image is reduced in size and those pixels in the cropped margin are discarded.


The Crop command on the transform toolbar for images crops the image down to the minimum enclosing box for the selection. If there is no selection the Crop command has no effect.


The simplest way to crop images is to use Select Box to draw a rectangular selection box and to then launch crop. The image will be cropped to the size of the selection box. This is fast and works the same way that "crop" functions work in almost all graphics software.


images\img_crop_eg05.gif images\img_crop_eg06.gif

In the image at left we've used Select Box to select the region enclosing Europe. We've used a Border selection style to show the selection. The image at right shows the result of the crop operation. The image has been reduced in size by the number of pixels cropped. It is shown on the checkerboard background within a larger image window.



Crop also works with irregularly shaped or discontinuous selections. Suppose we select pixels in South America as above.



Applying the crop operation using the Selection as the target will crop the image down to the size of the selection.




Image editing operations can be undone using Undo . The keyboard shortcut for Undo is CTRL-Z




Images can be zoomed in and out. Use the View - Zoom to command to zoom to a specific level. The Native zoom choice in the Zoom To dialog will zoom the image so that one image pixel is exactly one screen pixel in size.