Extraction Tutorial

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• Publié par: Awlau
• Nombre de lectures: 25
• Langue: English

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Extraction Tutorial
By Hummie


Everyone wants to know how to extract images! The uses are many, from extracting an
element from a scanned-in image (or photograph) for make digital scrapbooking
elements, to extracting people from backgrounds for layouts.

This tutorial is a basic extraction tutorial. To extract very fine items (ie. hair) would be
difficult with this tutorial.

If designing a digital
scrapbooking element, it is
important to place the
element on a 12 x 12 page
(the standard for
digiscrappers) and resize it
to be an appropriate,
realistic size.

The fundamental plan is to
delete all of the
background around an
element.

This is easier done if the background is all black or all white. My scanner has a white
background on the door. However, as can be seen by this example, the element cast a
blue shadow onto the background. This might have been easier to extract had I placed a
black piece of paper over the clip before closing the scanner door.

There are many tools and methods to delete backgrounds. Use your knowledge and
utilize them all, even if I do
not highlight them in this
tutorial.

Remember that selection tools
can be utilized to select the
area to be deleted and
thereafter hit the delete key on
the keyboard.

A good erasure tool to begin
with is the magic eraser.
Continually click on the
background to make it
disappear.
There are two settings on
the magic erasure which
are important.

The tolerance will effect
how large of an area is
deleted. In the
beginning, a larger
tolerance (approximately
30) is beneficial.

As the remaining areas to
be extracted are smaller
and closer to the element, a smaller tolerance (approximately 10) is beneficial.

It is important that the contiguous box be checked so that the magic eraser only erases the
parts of the background that are touching and not any areas of the same color within the
element.


There are several tests
that are helpful to learn
and to utilize often while
extracting.

The first test is to
activate the move tool so
that the bounding box
can be seen. Note that
my bounding box is
close to the element now,
which indicates that the
areas furthest from the
element have been
satisfactorily erased. (compare with first image above).












Zoom in (control +) to begin
using the standard brush eraser
tool. Use the bracket keys on
the keyboard ([ and ] ) to make
the brush larger and smaller to
erase larger areas or to fit into
tight areas.

Remember that there are
different uses for hard or soft
brushes.









To erase straight lines, you can
change the erasure brush to
“block” or make a rectangular
selection along the edge and hit
the delete key on the keyboard.




















I have finished erasing around the clip.

It appears to be a clean extraction, but it is
not! It is time to learn another way to test
the extraction.

















Hold down the control key and
click on the layer in the layer’s
palette to create a selection of the
layer.

In my sample, you can see many
marching ants in areas surround
the clip. Grab the eraser tool and
drag over these messies. Hold
down the control key and click
on the layer again. There should
be less straggling marching ants
than before. Continue erasing
and selecting the area until all the stray pixels have been deleted. Zoom in to look at
areas closer, especially around the element.





There! Now it is a clean extract!
Think again! It is time to run
another test.

Create a new layer and fill it
with black (or other colors as
needed, something that contrasts
the color of what you are
erasing).

More messies! Grab that eraser!
Zoom in really close to the
element and skim around it
looking for messies to erase.





In this sample, you can see the
marching ants around the
element; however, there remains
messies outside of the selection.

Why? These messies are so
faint and opaque that the
selection is not picking them up.

It is important to scan the entire
image zoomed in very carefully.
















Of course, using the erasure to delete these faint
messies is an option; however, there is a quicker
way.

Under the Select drop down menu, choose Inverse.

This will in effect now select all of the area outside
of the element, rather than inside the element.

Hit the delete key!














When you are satisfied
that the element is
extracted, click on the
eye to make the
background layers
invisible and use the crop
tool to cut the file down
close to the element
before saving as a .png.












There are two techniques for more advanced
extractions.

In my example, it was quite difficult to decide which
part of the metal should be deleted and which should be
kept. There is a method to compare the original scan
with the extracted image and put back in areas that
should not have been deleted.

Copy both the original scanned image and the extracted
image.

Leave the original extracted layer as invisible for safe
keeping. You may choose to use it as is later.

Place the copy of the original layer over the copy of the
extracted layer. With the copy of the original layer as
the active layer, hold down the control key and hit the
“G” key on the keyboard. This will in effect create a
mask. Only the outline of the extracted layer will be
visible on the layer above it.

Toggle the original layer on and off to see which areas have been erased that might need
to be included again.

With the copy of the extracted layer as the active layer, use the brush tool (any color) to
draw over the areas that should be added in (you can see I have added some red from my
brush to the metal area in my sample…look close!). If you add back in too much, switch
to the erasure tool to delete the area once again.



The best way to remove
jaggies is to soften them
with a blur filter.

If the above mask
method was used, you
may need to merge the
two layers before
applying the filter.

Hold down the control
key and click on the
layer in the layer’s palette to obtain marching ants around the element.

Under the Select drop down menu, choose Modify, and then choose contract. A popup
box will appear. For small elements such as mine, choose 1 and hit “OK.”

Important! Invert the selection.

After inverting the
selection, the small 1
pixel area on the outside
of the element is within
the selection.

Under the Filter drop
down menu, choose blur,
and then Gaussian Blur.

In the popup box, move
the slider and observe
how the edges of the
element smooth. Choose
a setting and click “OK.”
I used a radius of 1, but
this might vary
depending on the size of
the element.