Grey sky to blue: best approach?

[terrypin]

A while ago I had some great help here on turning a blue sky to grey. Now I'm trying the more familiar reverse,

I'm doing it on this Google Earth Street View image:
https://dl.dropboxusercontent.com/u/401 ... mVan-1.jpg

This is my first attempt:
https://dl.dropboxusercontent.com/u/401 ... luesky.jpg

I made it by selecting the sky, lightening it and then using the air brush with a blue chosen from memory (and a second time with a slightly darker blue). Apart from setting opacity at 40% I made no other changes to what was already there:
https://dl.dropboxusercontent.com/u/401 ... ttings.jpg

What method do the experts use please? Simplicity over high realism would be my priority, but it would be good to have both! Is there perhaps a well endorsed script?

--
Terry, East Grinstead, UK

[photodrawken]

Hi Terry,
Unless you're an excellent artist, I would not attempt to paint clouds and sky.

My first thought was to just replace the sky:
1. Promote the background to a normal layer.
2. Select the sky.
3. Delete the sky.
4. Paste a new sky as a new layer, moving it below the former background layer.
Of course, the lighting of the scene does not match the new sky, so I boosted the clarity, vibrancy and contrast so it would look more like a sunny day:

Uploaded with ImageShack.us

If you want to retain the original sky:
1. Select the sky.
2. Apply an Adjust...Color...Channel Mixer, boosting the blue:

Uploaded with ImageShack.us
3. Apply an Adjust...Brightness and Contrast, adjusting both the Blue channel and the RGB:

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to get this:

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Edit:
I think I overdid it with the Levels adjustment for the Blue channel -- that sky looks much too "sweet".

[terrypin]

Thanks a bunch, Ken, that first method is brilliant - embarrassed I didn't think of it myself!

I used the sky from a photo I took in same area at similar time of day:


As this will only be seen for about 6 seconds as part of a DVD, I'm happy with its quality.

--
Terry, East Grinstead, UK

[photodrawken]

I realize this is absolutely of no help for your current project, but in case anyone reading this thread is wondering about creating a cloudy sky, I thought I'd share this result:

Uploaded with ImageShack.us

I used and old (and somewhat rare) version of Kai's Power Tools -- KPT6 (yes, "6"), from the days when it was distributed by MetaCreations. Its "SkyEffects" is a plugin that allows you to build up your own cloudy sky, with beaucoup options. Although it can't create puffy cumulus clouds or mare's tails, it does an otherwise excellent job of creating a believable cloudy sky.