Re: [Gimp-user] First time user

[Steve Kinney <admin pilobilus net>]

On 04/13/2016 06:35 PM, apeterl808 yahoo com wrote:
> Hi everyone,
> First time user here! I’m trying to take an object (like a car and not the picture) and place it in a new 
> background. Any help would be appreciated!

Hey Peter!

The GIMP User list usually replies to questions like yours right
away, sorry about the lag.  It is a Big Question though.

In broad terms, you will open the image with the background you want
in the GIMP, add the image with the car (or etc.) that you want over
that background on a layer above the desired background, and remove
everything but the car (or etc.) from the top layer.

It's a Big Question because there are /many/ ways to remove the
unwanted part of a layer in an image while leaving the part you want
to keep intact.  The more complicated the outline of the part you
want to keep, the more it pays to use specialized tools and
techniques to accurately (or at least "convincingly") remove the
background.  Cars are usually fairly simple shapes with nice sharp
edges, and the "one best" way to remove content from an image layer
in the GIMP is usually by using a layer mask, so I will present that
method.

The tools and controls you will need include the image canvas, where
the image you are working on is displayed; the toolbox, for
selecting different tools to use on the image, i.e. tools for
selecting parts of the image, tools for painting on the image with a
brush, etc; and the Layers dialog dock.  These are indicated by
numbers 1 (Toolbox), 3 (Canvas) and 4 (Docks window with the Layers
dialog selected) in the picture on this manual page:

https://docs.gimp.org/2.8/en/gimp-concepts-main-windows.html

or https://tinyurl.com/gozowlm

It will also be MOST helpful to review section 4 of the online GIMP
manual, Common Tasks, before diving in:  If you open some random
image in the GIMP and do the things described (especially the
techniques that actually change the appearance of an image), you
will start to pick up the basics right away.

Section 6 of the online manual, Files, is also very important for
understanding how the GIMP saves images in its own XCF format, and
exports images into formats like JPG, PNG, GIF, etc.

https://docs.gimp.org/2.8/en/gimp-images-out.html#gimp-using-fileformats

or https://tinyurl.com/hyq2f8o

Now then:

Open the image file that will be the background of your finished
product in the GIMP.  Then drag and drop the image file with the car
from your file system browser (probably Windows Explorer) to the
image canvas (the background image).  The image with the car will
appear to replace all or part of the background, but look at the
Layers dock:  It now shows two layers.  The bottom layer is the
background image, the top layer is the image with the car.

If necessary, you can change the size of the car relative to the
background image by doing Layers > Scale Layer.  You can either
select this from the menu at the top of the image canvas window, or
right-click on the canvas and select it from the menu that opens on
the spot.

Play around with the Scale Layer commands in the window that pops
up.  As with text editors and similar tools, Control-z is your
friend:  It will undo the last thing you did.  Do Control-z again,
and the previous action will be undone, etc.  When the car is about
the right size for your finished image, proceed to the next step.

In the online GIMP manual, a tool called Intelligent Scissors is
described here:

https://docs.gimp.org/2.8/en/gimp-tutorial-quickie-separate.html

or https://tinyurl.com/z4gmvu4

Give it a try.  If the car in the source image has strong color
and/or brightness contrast with its original background, you may be
able to select it very accurately with the Intelligent Scissors
tool.  Once it is selected, issue the command Select > Invert, to
turn the selection inside out:  Now, everything /but/ the car is
selected.  Do Edit > Delete, or Control-x on your keyboard.  Look
over the results:  With luck, you will have accurately removed the
background around the car.

If so, you can turn off your selection (Select > Select None), turn
on the Move tool (the Toolbox button with a four pointed arrow
icon), then click and drag the car to position it where you want it
on the background, and you are more or less done.

If the car's outline has not been accurately enough selected, do
Control-z or Edit > Undo to bring back the deleted background from
your car layer.

You can either do Select > None and try again with the same tool, or
leave the selection outline in place and use it as a "pretty close"
staring point for making a very precise layer mask.

Add a layer mask to the car layer:  In the Layers dialog,
right-click the top thumbnail (the layer with the car), and select
Add Layer Mask from the menu that opens.  Accept the default (full
opacity).  Left click on the new rectangle that will appear to the
right of the top layer in the Layers dialog, to assure that the mask
is selected.

Back in the Toolbox, find the Color selector (a black rectangle over
a white rectangle), and drag and drop black onto the image canvas.
This will fill the layer mask with black in the area around the car
(still selected), making that part of the layer transparent.  The
result will look the same as deleting the non-car part of the layer,
but there's a big difference:  You can bring back as much or as
little of the "deleted" layer as needed, by painting on the layer
with the Brush tool.

Turn off your selection by doing Select > None in the main menu.
Then, select the Paint tool in the Toolbox (its icon looks like a
paintbrush), click the white rectangle in the color selector to
paint with white, and check out what happens when you click and drag
to "paint" on the edge of the car:  Its original background comes
back, right where you painted the mask white.  Back in the color
selector, set the color to black, and undo your last action by
painting with black in the same area you painted with white.
Congratulations, you are now using "expert" techniques!

To get really precise, you will need to zoom in close on the parts
of the image that need work.  Try this:  Hold down the Alt key on
your keyboard, and scroll up and down with your mouse wheel.  Zoom
in, zoom out.  Any time you are having problems with fine details in
an image, you can always blow them way up.  Note that the zoom
function more or less tracks on where the mouse pointer is on the
canvas when zooming in and out.

It will also be helpful to change brush shapes as required:  The
stock ones include hard and soft edged circles of various sizes.
Select the one you need in the Brushes dialog dock, which in the
manual image mentioned above is the left-most tab in the dock area
numbered 5.

At any time, you can save your work in progress by doing File > Save
or Control-s.  This will save your image as an XCF file, the GIMP's
native format, with all layers, masks, selections, etc. intact for
later modification if needed.  "Save early, save often."

When you are done tweaking on your image, save it one last time then
Export it:  That's File > Export or Control-e on your keyboard.
Type a name for the file, and give it the right extension for the
file format you want:  PNG is usually a good choice, although JPG
provides more compression (smaller file size), etc. as per the Files
in the GIMP online help docs.  The GIMP will recognize the file type
you want by the extension you typed, and present the relevant
options - defaults are usually good.

Hoping this intro was worth the wait,

Steve

:o)