cropping/masking a bitmap

[Mickie]

I was using Ross's wonderful freehand tool method of masking a photo (if you haven't already, see it here Ross's guest tut)when all of a sudden the main body of the photo was gone and I was left with a piece of sky. I realized that there must be some "rule" as to which part of the bitmap is masked...but I haven't been able to figure it out.

Anybody know?

Mickie

[Ross Macintosh]

Okay Alan of East Sussex - Draw a filled shape using the shape editor tool. Now you can use the freehand tool to edit that shape. To do so, select the shape and then bring the freehand tool's cursor close to the edge of the shape. As you do you'll notice the cursor changes to include a little wavy 'tilde' symbol. That is good - it means you are in freehand edit mode upon holding down the mouse button (do that). Move the cursor until it intersects again with the edge of the shape and the 'tilde' reappears - at which point, if you release the mouse button, part of your shape will have been swiftly edited away. Mickie's question related to the fact that (unless there's a trick) it is hard to predict which side of the freehand edit line will be edited away from the original shape. Try it and you'll see what we mean - try and predict which side will be edited...

Regards, Ross

<a href=http://www.designstop.com/>DesignStop.Com</a>

[heimo]

Thanks to Ross's guest tut! Here are some ideas to make it easier (to me?)
Draw a new shape over the importet bitmap. It could be a Help to apply transparence to look behind for editing the shape for a closer fit.
Then
You give Xara the advice to "arrange-combine shapes-lice(cut)shapes!" and You get the masked object. After this, you can apply feather region
to loose all the small not wanted spots around.
Put dow a new Background an this was it..

This Way shold be much faster than editing the Photo by itself with the shape - Editor- Tool.

http://www.salzburg.co.at/hmooslechn...finsternis.jpg

[Mickie]

Alan, I didn't keep the bird. It's a xara photo from the clipart gallery. I've got the feeling that you and Christine have come up with the general "rule" but there must be some sort of "i before e except after c rule" maybe it doesn't recognize nodes added or something.

Bob, your method works, but I have found I prefer snipping away background with the freehand tool until I'm close to the shape I want. Then I work with the nodes to get it right.

Mickie

[Mickie]

Christine and Alan...sounded good to me. So I started experimenting. I added a node to a partially masked photo. The section I wanted to keep had 4 nodes. I was stripping off a piece with three nodes...but was left with the wrong piece.(Illustration attached)


Maybe there are hidden nodes in there [img]/infopop/emoticons/icon_eek.gif[/img]

Mickie

[Bob C.]

The closed shape remains.

I must admit I don't use this technique much but when working on Ross's hair challenge I carefully traced Ross's image using the Freehand tool and closed the shape (no fill) Made minor adjustments with the Pen tool (not the Shape Editor tool unless I really needed it)

Selected both (the bitmap and my closed trace) then from the "arrange" menu picked "combine shapes/intersect shapes" and the background disappears.....every time. Well I tried 3 times [img]/infopop/emoticons/icon_wink.gif[/img]

[Mickie]

I was using Ross's wonderful freehand tool method of masking a photo (if you haven't already, see it here Ross's guest tut)when all of a sudden the main body of the photo was gone and I was left with a piece of sky. I realized that there must be some "rule" as to which part of the bitmap is masked...but I haven't been able to figure it out.

Anybody know?

Mickie

[Egg Bramhill]

This one is strange. I've been playing about with it since the original posting. I believe it is the node count that matters, but it seems to follow some rules.
If the image is sliced, with equal number of nodes on each side, delete the section that does NOT have the starting point within it. (Even if this is the larger shape)
If the image is sliced across the starting point, then the node count must be greater than 2 on the non starting point section before the section with the starting point is deleted. (Remebering to add the new added nodes to both sides in the count.

This sounds complicated, but I'll try to do a mini tut. (Not that its that important but it would be nice to know)
Egg

[ajreed]

I might know the answer if only I understood the problem. Now and again Xara surprises me, but there's generally a sound reason behind it.

I was always getting the stack order wrong when doing 'intersects' and ending up with the wrong fill. Now I learnt just how to do it predictably, and i suspect your little problem also has a simple rule that you are unwittingly violating.

So - some more detail please?

Alan

[Ed Nadie]

Egg,

I looked at your slicing exploration, and can suggest that straight and curved lines need to be differentiated. It's easy to verify that curved lines have more 'weight' than straight ones, and would help explain the seemingly inconsistent results.

These variables can probably be ruled out as factors:
» size of enclosed area
» relative density of nodes (or length of line segments)
» cartesian orientation (eg. top versus bottom)
» direction of the line
» chronology of changes (revisions, most recent operation, etc.)
» type of slicing line (doesn't matter if it's straight, wavy or loopy -- it will attach to whichever side wins the slicing derby.)
» type of tool used to create the shape.

What is left?
The mathematical complexity of the line as defined by the number of nodes and number of bezier tangent arms. That would probably be the simplest and surest way to predict the most important division of a shape.

It's clear that it takes two extra nodes (without handles) to overcome the advantage of a shape's starting point -- so the starting point would get a bonus weight somewhere between one and two nodes, call it 1.5 (it gets one point for just being a node, so that's total of 2.5; and more if it's got control handles).

I suspect bezier tangent arms probably have a similar weighting. (By comparing your examples nine and ten, you can estimate that each tangent line might be weighted about 0.7.) Nodes with two tangents likely have twice the additional weight of nodes with just one tangent line. Possibly the number and type of line segments (straight vs curved) is considered in addition to, or instead of the nodes. There may be other considerations, when shapes have donut holes, etc.

I like to draw with the freehand tool with lots of loops, and also use the 'join shapes' command a lot, so I end up with a single convoluted shape, and often ninety percent of my drawing will disappear when I try to redraw a small corner. I end up either deleting nodes individually, or draw a shape over a complex area I want to redo, and 'subtract shapes'. I hope someone from Xara will respond, because I've also wondered about this.

-- Ed Nadie