On 10/24/2012 09:03 AM, wallisonline wrote:
> Hi All,
> I am a complete n00b so apologies for the question... 
> I have myself a picture of my kitcar which I am looking to change the colour 
> of however I want to preview a selection of colours using GIMP to see how 
> they look on the car.
> Can anyone point me in the direction of a tutorial of how to "overlay" 
> different colours on the car or advise how I go about doing this? I am not 
> sure how to go about selecting just the body of the car so that I can overlay 
> different colours.
> I would prefer to not have to hand paint each colour over the body of the car 
> if it can be helped!


What you want to do is create a layer mask that isolates the painted
part of the car from the rest of the image.  What a mask does, is
similar to a stencil:  Where the mask is white, the layer's content
is visible in the finished image(s).  Where the mask is black, the
layer is transparent and the one(s) below it are visible in the
finished image(s).

I am sure there are good tutorials for beginners out there, but I
was not able to find one easily, so I will just describe the process
and hope for the best...

First you will need to open your source image in the GIMP, find the
Layers dialog, and duplicate your base layer (original) twice, so
that your working image becomes a stack of three copies of the same

Save the new image in .xcf format, and do Control-s on your keyboard
after every major step of the process below, to save your work in
case you are interrupted and/or "just in case."

Select the middle layer (left click with mouse on the thumbnail in
the Layers dialog), and drag and drop white (or any color) from the
color selector tool to the main image window.  This will change the
middle layer to one solid color.  Eventually, all your different
colors will go here.

Select the top layer, right click the thumbnail in the Layers dialog
and select Add Layer Mask from the menu.  Accept the default White
mask, which leaves the layer fully visible.

Now comes the painting.  Click once on the layer mask thumbnail in
the Layers dialog to make sure it is selected, then in the main
toolbox, select the paint brush tool and make sure the foreground
color in the color picker is black.

In the main image window, start painting over the painted parts of
the car with black.  Since you are paining on the layer's mask, and
making the parts you paint transparent, your result will look like
you are paining the car white.  That's the layer below showing
through.  In the process of paining the car, you will learn a bit
about how important it is to "zoom in close" for detail work, and
you will probably want to start by outlining the car with a small
brush.  If you hold down the shift key and click on the image, you
will draw a straight line from wherever you last applied 'paint' to
wherever you click with the mouse:  Play "connect the dots" wherever
possible to make the painting go faster.

Remember that you can tweak and fine tune your layer mask by paining
with white to "bring back" parts were the black "goes over the line."

Once all the painted parts of the car are one flat white outline,
you can start changing colors.

Select the base layer in the Layers dialog, and in the image window
do Colors > Desaturate.  You will not see a change in the image
window yet, because the two layers above your base layer are
blocking your view.

In the Layers dialog, select the second layer - the one with the
mask - and use the drop down menu at the top of the dialog to change
its mode to Color.  Your black and white car will now be
visible in the main image window.

Time to start changing paint colors:  Leave the second image layer
selected, open the color selector, and pick a color, any color.
Drag and drop this into the main image window to replace the white
in the second layer and viola, a colored car.  If the outline is not
perfect enough, go back to the layer mask and paint on it with black
and/or white to correct errors.

You can play with the Opacity slider control in the Layers dialog to
make the colored layer's effect stronger or weaker.  You can use the
"Colors > Hue / Saturation" tool's Hue slider to tweak the color of
your coloring layer, or drag and drop from  the color selector tool
to get brand new ones.

When you get a color you like, here's one good way to save it:

On your keyboard do Control-Alt-C.  This will copy the visible image
to your clipboard, including the effects from all layers.  Do
Control-V to paste this copy into your image as a new floating
layer, and click the New Layer button at the bottom of the Layers
dialog to anchor it as a new normal layer.

Drag and drop your new layer from the Layers dialog to the main
toolbox and viola, it opens as a new image.  Save this image in any
convenient format and close it.  Back in your Layers dialog, left
click the eyeball icon next to the new layer to turn it off, making
the layer invisible, and continue on to create your next color.

Repeat as needed.



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