Here’s a quick way of drawing a enlarged callout on an image using Omnigraffle.
To avoid pixellation in the callout, your original image will need to be bigger than the main image on the canvas. Place the main image on the canvas and scale it accordingly:
Draw a circle shape onto the canvas, then add another copy of the main image as the shape’s background using the
Set Image option in the
Image section in the inspector:
A scaled-down version of the main image will appear as the background of the callout shape:
Now click the
Manual Sizing button in the Image inspector to revert the shape background to full size:
Then click the
Mask button so that the shape is shown as an overlay on the fullsize image:
Now you can use the scaling grab handles at each corner of the shape’s background image to get the callout to the correct size, and move it so that the correct area is show in the callout:
Done button in the Image inspector will hide the full background image - at this point you can move the callout into the right place.
To show the zoomed area, drag another Circle shape onto the canvas and set its fill style to none. Now position it to show the area that’s enlarged in the callout. You can also adjust the border of the circles to make them stand out:
Finally, add two tangent lines to join the original area and the callout:
The end result is a neat callout image highlighting a specific area on the main image.