I've done a few like that - the way I did it was to take each individual image, Feather the edges, then copy/paste it to the main collage/montage image, and then tinker with the opacity .. seems to work ok, but there may be better ways?
This is in Photoshop 6 btw, but I think the Feather option was in 5 too.
That's pretty much how I handle it too... Pick one image to use as a 100% opaque background, and layer the others on top, with feathered edges. I'll generally use the lasso tool to select the image and then delete the outside area (with feathering). Then you can do touch up blending with a 0 sharpness eraser.
Of course, the super-pro way to handle it would be to position each image in it's own layer and create a transparency mask for each. Then you can alter the edge feathering, etc., on the mask without actually deleting the image itself. Just use a 0 sharpness brush to "paint in" each collage image on it's individual layer mask.
Yes retro, it's in 5 also.
>Pick one image to use as a 100% opaque background, and layer the others on top, with feathered edges
How about if there's to be no image to be used as a background, like doing 4 photos in a 4 portion square - or slighly skewed asymetrically, or side by side in a row, just placed on a background.
I edit the original images in PhotoShop 3, then composite them in Xara X, which is a great raster/vector program. Xara X has fantastic layering and transparency controls.
How about if there's to be no image to be used as a background
Pick a pattern that will coordinate smoothly/complimentarily (is that a word?) with all of the photos... Or, if the photos have a common element (trees in the background, water, clouds, etc.), pick the most "generic looking" section of one of the images and stretch it out to use as a background.
The point is just to have something to blend/fade the photos over, so there aren't any accidental gaps of solid color glaring out. I've found the "busy-ness" of using a photo as the background layer just makes the edges less noticable than using a solid color background, if there happens to be a slight gap between collage elements.
Generally, I do as the others (in PS6), create a selection around the image, invert it, set appropriate feathering and delete with a large eraser. Then drag that layer onto your final (where it makes a new layer).
When feathering doesn't give me the image "edge blur rate" that I want, I sometimes do another selection part way into the blurred area, invert, feather and do a Gausian blur filter - to get faster blur in less linear space.
In some collage work, I add visual elements that pretty much cover the whole image, to help integrate the elements visually, like an overall texture or pattern, a fuzzy larger B&W image directly behind an element, a few vertical & horizontal lines (like those drafting sketch lines cliche), etc.
Oh, and of course, I use Edit > Transform to rotate, scale, distort, etc. the collage elements/layers. And not all are 100% opaque, depending on their importance to the visual dynamics of the composition.
In addition to layers and masks, there are several blend modes (overlay, multiply, etc.) that can make more realistic transitions between layers. Sometimes even a faint noise filter can help unify an arrangement, or make a solid background appear part of the larger composition.
By using layer masks you can make subtle changes and modify as you go.
Fine touching those feathered edges with the eraser (a nice faded brush) is quite a handy way to perfect the finish.
In fact I tend to do the whole thing with the eraser - stick one layer on top of the other and carefully erase the bits I don't want (history brush at the ready, mind).
I tend to do the whole thing with the eraser
Generally, so do I. I keep meaning to work with masks more often, but the eraser is always SO handy.