How does contiguous work?

[gregd]

For many years now, I've ran into strange edge case behavior with Magic Wand selecting contiguous. Here's an example where I want to intersect select, resulting in the top and bottom intersections being selected:

With contiguous disabled, all three intersections are selected, as you would expect. With contiguous enabled, only the top intersection is selected for some reason. Changing tolerance doesn't effect anything, and all of the black segments are the exact same color.

If I try to click just outside the current selection, it results in no selection:

 Why does this happen?

[Brad @ Roaring Mouse]

Contiguous means it will select all matching pixels that are touching/connected. Non-Contiguous would select any matching pixel, touching or not. So when you select the area you did with Contiguous selected, there is no connection of black pixels within that selection, so, yes it would only select the top bar.

[gregd]

I'm sorry, I don't understand. If contiguous only selects "touching/connected" pixels, then why does this intersect select result in a disconnected selection?

 

 

[mglush]

Hi!

Here is anothre definiton that might help. This comes from a Google search:

In Photoshop, "contiguous" refers to pixels that are touching or sharing a common border. When a tool with a "contiguous" option, such as the Magic Wand tool,is set to contiguous, it will only select pixels of a similar color that are directly adjacent to each other. If contiguous is unchecked, the tool will select all pixels of the similar color on the entire layer, regardless of whether they are connected. 

Here is a video that might help: https://www.youtube.com/watch?v=QKB08u3UXEk

[gregd]

Aren't the two selected regions in the second image in the comment that you replied to not "touching or sharing a common border"?

[mglush]

Hi! What option for the Selection tool is checked in the Options Bar? Can you show us a screenshot of your window with the panels and layers visible, and not just the image? That would help immensely.

It looks like you might have the Intersect option checked in the options bar, but I cannot tell unless we can see the Options bar and what layer you have selected. 

What are you trying to select?

Michelle

[gregd]

Yes, as I mentioned in my previous posts, I am using intersect select. Here you can also see my layers panel:

 

[mglush]

Just to get a feel of what contiguous does, click back onto the regular selection option in the Options bar, then click on an image with the magic wand tool. This might give you a better understanding of what contiguous does. With contiguous selected, you will only select pixels that are touching that meet the tolerance criteria. With it not clicked--it will select everything within that tolerance level.

Michelle

[gregd]

Thanks, I have a basic idea of how contiguous usually works, but I'm more interested in the examples I've shared here. How exactly does contiguous work? If it only produces selections that are connected, why I am sometimes (but not always) able to produce disconnected selections with contiguous on?

[mglush]

Hi!

The definition of Contiguous actually means sharing a common border, or touching. So, Contiguoulsin this case means that everything that is the same color—and is touching the area you have selected will be added to the selection. When Contiguous is checked it selects only the areas that are similar and touching, and when it is not checked, it selects all areas that are similar to the area you clicked but are not touching.

I hope that helps!

Michelle