Use the Gradient Tool on a second layer layer, and then blend them together with the opacity slider. Set the Gradient Tool to either a straight or a Radial blend, and set the color to white.
I do this for some vingettes also - set the Gradient Tool to black or white as desired, use a Radial Gradient.
First, make a selection with the Marquee Tool and Feather the edge at 250 pixels, Invert the selection, and then use the Gradient Tool to darken the edges or lighten the edges depending on whether the Gradient Tool is using black or white ink.
I don't have photoshop but in the GIMP I'd try creating a layer filled with solid white on top of the image, then editing the mask of that layer and using a gradient fill to make the mask change gradually and smoothly from opaque to transparent (i.e. full white to transparent). I'm sure you can do the same in photoshop I just don't know what the various tools so I can't give a more detailed explanation.
Here is Photoshop speak for what dancorder is saying.
Add a layer filled with white.
Then go the Layer Mask->Reveal All (or some such, I don't remember the exact names) so the layer mask shows up.
Then select the new layer's mask channel.
Fill it with the gradient of your choice.
Once you've got it where you want it, you can flatten the image.
Wow, thanks everyone for the rapid responses I'll give these methods a go, you'd think, or at least I thought there would be a simple tool that just says, OK you want to fade this image to white, tell me in which direction and at what rate and I'll do it for you, rather than having to mess around with layers.
It is just that you have so much more control of any editing done on a Layer that we all tend to do it that way as it is non-destructive.
Using the Gradient Tool on the background layer ( ie: without layers) will work to create a gradient of black or white, but does not allow blending modes, and can't be reversed.
Comments
I do this for some vingettes also - set the Gradient Tool to black or white as desired, use a Radial Gradient.
First, make a selection with the Marquee Tool and Feather the edge at 250 pixels, Invert the selection, and then use the Gradient Tool to darken the edges or lighten the edges depending on whether the Gradient Tool is using black or white ink.
Moderator of the Technique Forum and Finishing School on Dgrin
Edit: Pathfinder beat me to it
Add a layer filled with white.
Then go the Layer Mask->Reveal All (or some such, I don't remember the exact names) so the layer mask shows up.
Then select the new layer's mask channel.
Fill it with the gradient of your choice.
Once you've got it where you want it, you can flatten the image.
Charlie
It is just that you have so much more control of any editing done on a Layer that we all tend to do it that way as it is non-destructive.
Using the Gradient Tool on the background layer ( ie: without layers) will work to create a gradient of black or white, but does not allow blending modes, and can't be reversed.
Moderator of the Technique Forum and Finishing School on Dgrin