So coming back to the "Have a Look" post...
The interesting thing about the flipping images and not being able to see the change without careful examination of the image is...
The brain creates a vivid crystal clear picture of what you are seeing. Yet your eyes can only see a small area in focus. The brain relys on the eyes ability to rapid move and focus on things to create the illusion of crystal clearness.
Seeing changes comes from the peripheral vision. The part of the eye that dosn't see the world all focused.
The flipping of images in the java app flips the images with an intermediate gray image (colour -> grey -> colour) pretty much obliterates the peripheral visions ability to notice the change. So to find the changes you have to use your "in focus" vision and interpret the image and analyse the image till finally you look at the right spot. Once you find the right spot its easy to see the change! In fact its obvious! If you show the changing images to another person it seems embarrassingly obvious whats changing, yet they too will struggle till they work out whats changing.
So how's this useful? In software UIs if you are designing something that's animated and changing and you know its animated and changing it can be very obvious to you what is changing. However, for someone who doesn't know what is changing you are relying on their peripheral vision to pick up on those changes. If there is too much noise then someone won't pick up on that change. Yet it will seem obvious to the designer what is changing. Sometimes the obvious is not obvious.
Oddly enough this issue cropped up at work where we were creating an animation of many fruit moving down a machine and getting tipped at various locations down a machine. A co worker and I were having a discussion about whether some of the animation changes were obvious or not. The person who created the animation felt it was "obvious", where as I felt that some of the changes got lost in the noise.
The lesson of the story is to test your designs with people who aren't the designers.
And the moral of the story is the obvious isn't obvious. It's embarrassing how often I forget this when I try to explain what seems "obvious" to me.