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Tutorial for Gimp - Layers and Selective Parts of Processing
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Jade O.

1064 posts
  [1 of 21]  Posted: Sat Jul 6, 2013, 10:21 (2179 days ago)
Modified: Mon Jul 8, 2013, 13:17 (2177 days ago)

Alberto deleted his previous tutorial, so here is an introduction for beginners.

Post questions at the end and either myself, or others, I'm sure, will do our best to answer them.
My techniques are self-taught so there may be better ways to do what I am showing you here.
The idea is to get newbies started working with GIMP.

Start by googling "GIMP" and download the file. It is a free download and very similar to Photoshop.
GIMP is constantly being updated so while what you get may look different, the way all versions work is pretty much the same.

You can do almost anything with GIMP but let's start with the very basics
-- how to selectively adjust parts of your image and how to work with layers.

Selective adjustment is valuable if you want to adjust parts of your image without changing the whole.
Layers is just like it sounds, you can layer one image on top of another.

Once you download GIMP you should end up with a desktop icon you can double click to open the program.

You should see a <Toolbox> window and a <GIMP> desktop working board window.
If you get the <GIMP> but not the <Toolbox> try clicking on <Tools> on the menu at the top of the GIMP window.


(And right off the top, click <Edit> and in the drop down menu that appears, note you can click <Undo> to undo whatever you just did that didn't work out.
Keep that in mind as you work through this -- it may come in handy.)

Then, click on <File><Open> to open an image.


An <Open Image> window should appear. Click through the menu to find your chosen image.
Here I clicked on <My Pictures><Panachallenge Images><Fort York 1.jpg> to get to my chosen image which I can see in the preview window.


Double click on the image to open it.


Congratulations! Take a break and grab a coffee!

Jade O.

1064 posts
  [2 of 21]  Posted: Sat Jul 6, 2013, 10:38 (2179 days ago)

O.k. Note how the cursor arrow in our last image is pointing to the lasoo tool known as <Free Select>.
Click on the tool and draw a rough circle around the girl's face.
Note the circle is very rough.
To make a smooth line AND to create a very soft edge (a gradient across the line)
note that BEFORE I started drawing, I clicked the <Feather edges> box and moved the slider <Radius> to 100%.


When the circle is completed (sometimes you have to click once or twice to make it join) note how my rough circle becomes smoother.

Now I go to the drop down menu at the top, and click on <Colours>
and choose <Brightness-Contrast>.


Adjust the sliders and ... magic!


Congratulations! Time for another coffee and to walk the dog!

Jade O.

1064 posts
  [3 of 21]  Posted: Sat Jul 6, 2013, 10:46 (2179 days ago)
Modified: Sat Jul 6, 2013, 18:57 (2179 days ago)

Now sometimes you want to work on a small area and be very precise.
Or your eyes just aren't what they used to be.

You can zoom in and zoom out without changing the image size
and move the close-up of your image around using four controls shown here in red.

Note by highlighting the % in blue using your cursor, you can type in any percentage you want.
Here I typed in "150%".

While we're at it let's lighten the inside of the hat to make it look like the sun is coming in.
I chose a close-up of the image because it makes it easier for me to draw with the free select tool closer to the edge of the hat without going over the edge
- I want to brighten the underside of the hat and not the background behind it.


Time for another coffee and to check to check the mail.

Jade O.

1064 posts
  [4 of 21]  Posted: Sat Jul 6, 2013, 11:01 (2179 days ago)
Modified: Sat Jul 6, 2013, 19:22 (2179 days ago)

O.k. after highlighting both girls faces using the free select tool and the brighness-contrast sliders
I now want to change the background.

For this we move into the exciting world of Layers.

First we open the Layers dialogue (Layers Window).
<Windows><Dockable Dialogues><Layers>


Note we have our image showing in the Layers Window (just one image right now).
(The first image is always called Background.)
Notice as well at the top of the GIMP window it reminds us there is just one layer open.

To open another, go to <File><Open as Layers>


Just like we did before, choose an image, in this case, Fort York 7.
I chose this one because I want to replace the condo towers and highway
behind the girls with the sky behind the soldiers.
Notice how the image (soldiers) is on top of the other image (girls) and you only see the top one
but the other one is still there in the background (see the Layers window for proof).


If you want more proof, move the slider in the layers window to fade the top image a bit.
Play around with clicking the <eye> in the Layers window on and off and notice the image you are working on is the one that is highlighted in the Layers window.
If you can't see what is happening when you are working, check to see you have highlighted the right image in the Layers window and the eye is turned on.


Time for another coffee and to feed the plants.

Jade O.

1064 posts
  [5 of 21]  Posted: Sat Jul 6, 2013, 11:09 (2179 days ago)
Modified: Sun Jul 7, 2013, 07:28 (2179 days ago)

Now let's use our free select tool to highlight the part we want to cut out.
How do we get the girls back on top so we can see what we are working on?
Well we can do a number of things, move the slider on the soldiers image to zero,
or click off the eye beside the soldiers image, both in the Layers window.
Or we can use the up -down arrows in the Layers window to move the girls' image on top.
Just make sure you have highlighted the image you want to work on by clicking once on the name of the image in the Layers window to highlight it.
(Click twice on the name in the Layers window if you want to change the name of the image in the Layers window.]

Note also, though not shown in a screenshot, this time we want a sharp edge to make a clean cut to remove the condo towers and highway.
We don't want a gradual (gradient/fuzzy) transition like we did lightening around the girls faces when we chose 100% Feather Edge for that.
So BEFORE we draw the line between tent and highway with the Free Select (lasso tool), we clicked off the Feather Edge box or moved the slider to zero to make a sharp edge and a clean cut.


Now <Edit> and <Cut>.
Notice the Layers window in the screenshot above.
The "eye" in the "Fort York 7" layer is turned off which makes it is invisible so we can see the "Background" layer lying below it which is the one we want to work on.
The image layer named "Fort York 7" is highlighted but we want to cut on the image layer named "Background".
So in the Layers window BEFORE we cut, we highlight "Background" by clicking once on the image layer name "Background" as shown in the screenshot below.


Notice after we cut the condo towers are gone but the background is white, not blue sky.
To get rid of the white we first need to clear an alpha channel. (alpha is transparent)
<Colours><Colour to alpha>
That grey checkerboard is GIMP's way of showing a transparent surface with no layer turned on below it.


So in the Layers window, click on the eyes to make both <eyes> visible (both layers turned on)
and/ use the up and down arrows in the Layers window to make sure the right layer is on top
and you have the finished image!


Now we need to <flatten> the image to meld the Layers into one.


Now save (but change the filename by typing over the name of the image in the save window so you don't
write over and replace your original image when you save your new creation.)


And you're done!

Time to relax but....no more coffee!


1528 posts
  [6 of 21]  Posted: Sat Jul 6, 2013, 21:00 (2179 days ago)

Wow Jade O!

What a great service you have offered to Panachallenge! I think I'll make this a sticky so it won't fall down in the threads!


613 posts
  [7 of 21]  Posted: Sun Jul 7, 2013, 06:27 (2179 days ago)

 mrsawyer wrote:
Wow Jade O!

What a great service you have offered to Panachallenge! I think I'll make this a sticky so it won't fall down in the threads!

thanks to mrsawyer I was wondering how I was going to retain easy access to a BRILLIANT work by JadeO

Jade O.

1064 posts
  [8 of 21]  Posted: Sun Jul 7, 2013, 06:53 (2179 days ago)
Modified: Sun Jul 7, 2013, 06:53 (2179 days ago)

Thanks. I hope this helps someone.

What I would ask is that anyone let me know if it worked for them and if there is any part of the explanation which confused you.
If I worded something in a confusing way for you, it would probably be confusing for someone else so the best thank you I could get is
1) people letting me know this helped and 2) how to make the explanation even clearer.

I wanted to post this because the learning curve for anyone new in post processing is steep
and there are a million GIMP tutuorials on the web but finding one for the basics like this isn't always easy.


12 posts
  [9 of 21]  Posted: Mon Jul 22, 2013, 03:19 (2164 days ago)

I have been playing with Gimp trying to follow the instructions, I have come up against a problem where the second picture doesnt cover the entire first picture. What next?

Jade O.

1064 posts
  [10 of 21]  Posted: Mon Jul 22, 2013, 09:54 (2163 days ago)
Modified: Mon Jul 22, 2013, 10:04 (2163 days ago)

Layer>Scale Layer

to change the size (vertical and horizontal dimensions) of a layer.

(This has nothing to do with the "zoom-in" and "zoom-out" feature shown above in the screen shots where the percentage is shown inside the red circle. Zooming in and out does not change the actual size in kilobytes of the image nor the relationship in dimensions of one layer to another.)

You can check the drop down menu under the headings of <Layer> or <Image> and you will find various ways to change the size of your layers/images. You can scale upsize or downsize. And you use "Fit Canvass to Layers" in the appropriate circumstances to expand or shrink your working area.

If it is still unclear then it's not you it's my explanation and others will have the same problem, so let me know and I can post a screen shot.

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