Photo montage with b/w to full color gradient

I've been stuck with the unlucky task of creating a wraparound for a product which will require a photo wraparound (4 in. height) around the cover a book. However, the photos will be from 5 generations: 1950s
60s
70s...up until now, you get the point. It will probably include 5 or 6 individual photos taken from those eras.

The hard part, however, is the transition gradient they must have:
a full b/w to full color transition from the back of the cover to the front.

(In other words: How in God's name do I go about creating a black and white-to-color transition across these pictures??)

Any help would be greatly appreciated.

fetus

This is a fun problem, and here's what I did...

First put all of your pictures together in the way you want them. You know, make a montage or whatever they call it. Don't worry about them being in color, just make them blend the way you want them to.

After all of that is done, merge all of those layers together.

Now go into Quick Mask mode. (Press Q)

Now select the gradient tool and make a white to black gradient from the left to the right.

Now go back to regular mode. (Press Q again)

Go to Image > Adjust > Desaturate. (Or press Shift + CTRL + U)

That should give you the effect you are looking for. You may need to play with the gradient some to get the progression from black to color the way you want it. But that gives you the general idea. Good luck!

I'll add in another method... If I had to do such a thing, I'd probably do what Deker would do, line up all the pictures at full color. and then merge them together.

I would then ctrl-click the merged layer, go to edit>copy, open a new document, and edit>paste the merged graphics into it. Then I would change this graphic's mode to grayscale. Why would I do this? Changing a graphic to grayscale results in a different graysccale look than desaturating in a rgb-mode graphic. Desaturation can sometimes make colors look the same, washing out some of the detail. Going into grayscale mode for some reason uses a different scheme to change the rgb colors into a black and white form. The desaturated colors are more defined for some reason.

I would then convert this graphic back into rgb mode and drag it back into the other color document. Place it directly above the other, merged full color graphic, and add a layer mask. Use the gradient fill-tool to fade the b&w pic across the color one.

Not much more different or difficult, but Photoshop has strange color differences you may or may not like, depending on your own personal tastes.

Thanks a lot for your help, guys. I appreciate it.

mrbogus, I do have one more question for you: do you forsee any problems w/ your rgb/grayscale tecnique if I had to submit the finished product as cmyk? would cmyk have more distinct color variations, or would it roughly produce the same look as rgb?

thanks for your help, I'll make sure to be in touch to show you the finished product.

Oh. I totally forgot about the CMYK part of your job. If you don't want to leave CMYK color space, don't change anything to RGB, just keep the original as a CMYK picture. Do all the steps I said, just replace any time I mention RGB with CMYK, and the effect would be the same, except in CMYK color-space, of course.