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New to Gimp Need Help Replacing Sky

Jul 8, 2013, 04:14
Post: #1
New to Gimp Need Help Replacing Sky
Hi everyone,

I am very new to GIMP and have been looking at a lot of You Tube Tutorials about GIMP and how the different tools work.

I just purchased a Canon SX50 and am currently using Picasa as my photo editing software, but some of my photo's have a washed out or sometimes white sky. I have taken some photo's of blue cloudy skies that I would like to use to replace skies in different photo's. All the You Tube videos showing how to do this leave out steps and some are just way to confusing. I have tried a couple of times, but it does not work. I really need some help please.

Thank you in advance
Lori

P.S. I have added 2 attachments, of the photo of the washed out sky and the photo of the sky I would to replace it with.


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Jul 8, 2013, 06:50
Post: #2
RE: New to Gimp Need Help Replacing Sky
Sky on the first layer.
Main image on the next layer above, add layer mask and alpha channel to this layer.
Use the erase tool to erase the sky, if you erase too much switch the foreground/background colors.
The trees will be very time consuming.
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Jul 8, 2013, 07:00
Post: #3
RE: New to Gimp Need Help Replacing Sky
In addition to Iwhistler's alpha channel/layer mask, you can add a Guassian blur(see Layer mask; step 4 below) to lessen how much you need to erase/clean up around trees.

I've had this problem too, look for "How to counter-act exposure washout" below my tutorial.
Layer Mask or Fuzzy Tool select way(alternately select by color tool)
Layer mask
(put the cloud layer on the top, lake image layer underneath)
1.Right-click cloud image and click on "Add layer mask"
settings: Selection
2. You will see two boxes on your "cloud" layer. Click the blank one on the right
3. Erase the sky area of the lake, while still on the cloud layer. don't worry about erasing part of the trees, as long as your on the mask(cloud layer) the lake layer will still be saved/untouched & we'll clean up the clouds in a bit.
4. Filter > Blur > Gaussian Blur Settings: 30 pixel both Width & Height
5. Erase any extra clouds over trees(if any) with a soft brush(Hardness 50 or below)

Fuzzy Select tool(magic wand)
http://docs.gimp.org/en/gimp-tool-fuzzy-select.html

1.Size the clouds layer to the upper right corner like I did in the "Layer mask" (upper-right corner)
2. Have lake image layer on top of clouds layer
3. Right-click lake layer & "add alphah channel"
4. With lake image layer selected, use the "Fuzzy Select Tool" Click on the sky, push delete.
5. Do any clean up(alt + erase) work on the lake layer. Then flatten the image (Image > Flatten Image) then save(File > export...')

counter-acting washed-out parts of image with camera

1 With the camera on a tripod, find the exposure setting on your camera. You'll take two pictures,
The first picture with normal exposure(0).
2 The Second picture on a lower exposure setting (until you can see the clouds, everything else will be darker, -1 to -9 or however low your camera goes, only until the clouds are more visible)
3. You'll put both images in Gimp together. Then just play around with the layer mode(near top of layers window) to get a composite picture(with both sky and lake visible)
If you can't get a good layer mode, try the "Fuzzy Select tool" on the lighter picture.

Hope this helps!


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Jul 8, 2013, 09:17 (This post was last modified: Jul 8, 2013 10:25 by rich2005.)
Post: #4
RE: New to Gimp Need Help Replacing Sky
This is the fringing that Ofnuts referred to: the blue around the trees.

Do not know the way he fixes it but I use this.

edit: - sorry. On the full image, this of course wrecks the lake - you need to make a selection of the skyline + trees first.
-------------------------
Colors -> Hue saturation. Look at whatever is in your image.
In this I started with the blue. Pulled the blue saturation right down.

like this comparison screenshot: http://i.imgur.com/FzAwuNJ.jpg

Still a little cyan around so as a completely separate operation, do not try all at once. Pull the cyan saturation down.

another comparison screenshot. http://i.imgur.com/YRp2roC.jpg

and you should see an improvement.
------------------------------------
Next is the layer mask, all sorts of ways, as above. There was a similar question here in the past. I made a short video of 2 ways to make a mask and a bit about 'touching up the defects ' right at the end.
A quick stab at your image and be prepared for a bit of pixel level painting in the layer mask.

LOL. I deleted the video from youtube so I had to re-uploaded.
http://youtu.be/0oWzfAlD5jM about 5 mins.

Might give you some ideas on how to proceed.

edit again: my stab at it, using the threshold tool to make a mask. But lots of faking around the treeline, still a few white pixels there. Very lucky that the reflection in the lake is not too far away from the new sky


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