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"How to" eraser tool ?

Aug 3, 2011, 05:35
Post: #1
"How to" eraser tool ?
Greetings,
I have an image of clouds against (multi)blue sky.
And i would like to remove the blue sky, and show just the clouds.
I clicked on Eraser, then selected a brush.
But no eraser circle appeared.
Pls, how can i use the eraser tool?
Thanks...vmars316


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Aug 3, 2011, 06:48 (This post was last modified: Aug 3, 2011 06:52 by ofnuts.)
Post: #2
RE: "How to" eraser tool ?
That's the way to use it. Make sure you have a layer selected in the Layers dialog.

By the way, there are two much faster ways than using the eraser Tools for this.

Low tech, little control on result, but damn fast:
- Use the color picker to set the foreground color. Use "sample average" with a wide area. Pick the blue in the sky
- Colors/Color to alpha
- Click on the color selector, then, in the color dialog, in the color picker, and pick your foreground color from its display in the Toolbox
- OK, done.

Higher tech, still quick, with a lot more control on the final result: open the Channels view: you'll notice that the Red channel is about black where you have blue, and whitish in the clouds. We are going to use that to make the image transparent in the blue. So:

- In the Channels dialog right-click the Red channel and "Duplicate channel".
- Layer/Transparency/Add layer mask, and initialize with the channel you just created.
- Start the Levels tools (will act on layer mask). Use the "logarithmic" scale (icon at top right)
- In the "Input levels", drag the left handle to the beginning of the histogram (insures that we have some fully transparent pixels), around 64. You can make the clouds look sharper by going further (80-85)
- Drag the right handle down (insures that some of the clouds is fully opaque). A value of 200 looks good.
- You can adjust the progression of the transparency by moving the middle handle.
- OK when happy with results
- Layer/Mask/Apply layer mask

If you are grafting the clouds in some other image, this procedure is better used after inserting the layer in the target image, so that you can see the final effect while playing with the levels.

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Aug 3, 2011, 20:27 (This post was last modified: Aug 3, 2011 20:29 by vmars316.)
Post: #3
RE: "How to" eraser tool ?
I tried your first solution, but no go.
I get lost if names you give don't jive EXACTLY with actual label names.

It took me a half hour to find the 'channels view'
Eventually, i fired up my 'agent ransack' searcher
and searched 'C:\Program Files (x86)\GIMP-2.0\share\gimp\2.0\help\en'
for *.* 'channel view', and found 87 *.html files where it is mentioned,
and 47 *.html when searching for 'channels view'

Anyways, i need to back up a bit and ask:
"Once i have selected a TOOL, say colorPicker"
and i want to disable colorPicker,
how can i get back to 'Point Tool'??".
Like when i first start gimp, all is new, and no tools are selected
and just the Point Tool is active.

Anyways,
(huge request)
could someone turn attached 'gimpLeftBottom-01.gif'
into a transparent gif, with no blue left, and only cloud showing.
And show me how it is done.
Or maybe there is a YouTube showing 'how to do'?

Thanks...vmars


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Aug 3, 2011, 20:59
Post: #4
RE: "How to" eraser tool ?
Channels view: in the main image window menu bar: Windows/Dockable dialogs/Channels. And if you google for "gimp channels" the first link is: http://docs.gimp.org/en/gimp-channel-dialog.html

Word of advice: don't use GIF. PNG supports transparency a lot better than GIF. See http://gimpforums.com/thread-pros-and-co...ge-formats

You've got all the necessary instructions above. Just do your part of the work. Given your current skill level, use the first technique.

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Aug 4, 2011, 00:16
Post: #5
RE: "How to" eraser tool ?
(Aug 3, 2011 20:59)ofnuts Wrote:  You've got all the necessary instructions above. Just do your part of the work. Given your current skill level, use the first technique.

Ah, I see what's going on:
1)
When I select Eraser, then move it over image,
I can see the WhitePointer and a small White rectangularBox.
But the PaintBrushCircle is so faint that I didn't see it.
It is too faint for me to work with comfortably.
?? Is there a way to make the circle line thicker ??
2)
?? How can i switch back to the PointerTool, from the currentTool ??

Thanks...vmars
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Aug 4, 2011, 00:41 (This post was last modified: Aug 4, 2011 00:42 by ofnuts.)
Post: #6
RE: "How to" eraser tool ?
1) Menu "Edit/Preferences" > "Image Windows" tab, "Mouse pointer' section: you can define if you see the mouse pointer and/or the brush outline for the paint tools. You can have both. But there is no way to make the line more visible (but if you also have the pointer then it's easy to find).

2) There is no "Pointer tool". There is a "Pointer dialog" that shows information about the pixel under the pointer, whatever the current tool. If you want a tool that won't mess the image, use the "Measure tool" (Compass icon).

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Aug 4, 2011, 04:49
Post: #7
RE: "How to" eraser tool ?
(Aug 4, 2011 00:41)ofnuts Wrote:  1) Menu "Edit/Preferences" > "Image Windows" tab, "Mouse pointer'
2) "Measure tool" (Compass icon).

Ok,Thanks
both are helpful.
I am getting the hang of it, see attach.
...vmars316


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Aug 4, 2011, 07:12
Post: #8
RE: "How to" eraser tool ?
This won't give good results when you import it elsewhere because it lacks progressive transparency. Try this (used the 2nd technique above):

[attachment=588]

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