On 2004-06-15 21:27:09 -0400, "Gene Palmiter" said:
I am reading this with baited breath…sushi for dinner….and I have yet to find a tool that makes the job of knocking out and object easy. So…I do it the hard way…."Z" and zoom in real close to and edge of the object. Hit "Q" for quick mask. Draw in the mask using a hard edge brush of about 5 pixels. Use "Space" to creep along. Draw the line along the outside of the object and all the holes inside. Fill the mask with the paint bucket…..hit "Q" again to change mask to selection and see if there are any marching ants where you don’t want them. Select/Inverse…make path…save path…make clipping path (for layout) or Ctrl-X to remove background….or copy object to another layer.
This is one of many techniques you can use; probably the most time-consuming, but occasionally necesary for really complex objects. But first let’s get to the OP:
What you’re talking about when you say "knockout" needs to be translated into Photoshop concepts (as well as jargon). You want to move a particular item, area, set of pixels, et al, from an image, so fundamentally your task is to make a _selection_. What you do with that selection – cut it out, paste it elsewhere, use it for a pattern – is trivial. In order to learn the technique, you need to know that term "selection". That’s your search key for help files, the web, and so on.
There are many ways to make selections: tradtional selection tools (marquees), painting tools (erasing and masking), a special tool (magic wand), and adjustment and editing tools. Selection is a critical skill, and even for a short project, you should spend some time learning how to be proficient with the selection technique that is most useful. [Not to pick, but the poster above is using a method that while sometimes necessary, can often be avoided. I tend to use it too much myself, because it’s comfortable.]
What you’re asking about – the straight line – involves using one of the marquees. As someone mentioned, there’s a polygonal lasso – a kind of marquee – that will allow you to create a selection marquee that has straight edges. You pick the poly lasso, and click on points around the part of the image.
You can also use the regular lasso. Holding the shift key will constrain the current segment to either a vertical or horizontal line. There’s also a magnetic lasso that you can read up on.
This poster (above) is describing a way of using a mask to literally paint a channel that determines your selection. Check the help for "Using Masks to Create a Selection" and "Quick masks". A similar method is to just duplicate the image, and use brushes to paint out around the image. When you’ve got an object against a white background, it’s easy to use a wand to select the background, and then invert the selection.
The magic wand is a special kind of selection tool that will select parts of an image based on color, and there are lots of options. This is a tool you should learn, as it is one you will probably use more than any marquee!
You can also select by color, using Image > Adjustments > Selective Color.
Finally, there is the Extract filter. This will allow you to make a quick selection, then deal efficiently with complex edges, such as hair. Check the help for "Extract" and ‘Smart Highlighting" . The example in the User Guide shows a picture of a furry buffalo. This is something you should definitely read about.
—
No sig, no neuroses