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How To Knock Out the White from an Artwork



There are several methods for this, each suited to different purpose.

Here I shall outline briefly each, starting with the one I use most myself- the Extract Filter.

1) The Extract Filter


This filter is designed to help you select otherwise tricky to select imagery- tree branches, hair, smoke, etc.
There are plenty of other guides around if you'd like to learn the conventional methods of using it.
The following though exploits a kind of bug in the filter that lets you to easily convert any white value in a pixel to a proportional value of transparency. [more...]

To save you the trouble of doing any drawing I'll be using this image to demonstrate the technique:

screen grab of before

It's not essential but for best results your drawing should be scanned at a good resolution and greyscale.

1) First- Save, then, If your drawing is the Background layer, double click it and give it a name to make it an ordinary layer.
The drawing should have no holes or gaps around the edge, bits of it that are already transparent will mess up this technique.
Now go Filter > Extract... and make sure you are using the Edge Highlighter Tool (at the top of the Extract tools palette, top left).
With a largish brush size, paint green selection colour all over drawing except for a few pixels at the top left corner of the image.
This is essential, and note that we are assuming here that there is no drawing in this area of your image, it is likely white space anyway.

screen grab of extract, green shown

2) Just check the check box for Force Foreground and leave the other settings alone.
Click once within the Colour rectangle to open the colour picker and choose the colour of your drawing.

screen grab of extract, colour 100k shown

If you drew it in pure black then choose the same colour from the Colour Picker.
If you drew it in red marker pen (why would you do that?!) then choose that colour.

You can use the Eyedropper Tool from the Extract tools palette to sample from a good thick area of colour within your drawing if you want to do it that way.
Disconcertingly, you do this by sampling from the image in the Extract panel, which has the green all over it!
It can be really useful though if your drawing is done in pencil, which is never really pure grey or black unless you convert it to be so.

3) Now you're ready to go- click OK.

You should find your drawing looks faint and all that was white is now Photoshop's transparency chequerboard pattern, or whatever layer shows through under the drawing.

Troubleshooting:


Against white, this transparent drawing should look the same as it used to.
If you feel you've lost something in the process then duplicate your new semi-transparent drawing layer and play with the duplicate's transparency slider or erase parts of it to suit.
You can merge the duplicate layer down when you're done.
If only a quarter of your drawing's been done or some other weirdness is going on then something's gone terribly wrong somewhere.
You shouldn't have to use Extract more than once on your image with this technique so Revert To Saved, review this guide carefully and start again from step one.

Remember-
if your drawing is on white in pure CMYK black (100%k and nothing else) then selecting Photoshop's default pure screen black won't give you good results, and vice versa.
See these screen shots for a demo:

screen grab image after extraction 100k screen grab image after extraction normal black
test: ignore this box


More to come...



2) Multiply


Not much of a trick this one.
Just alter the blending mode of the layer containing your drawing to "Multiply" and bang- the white is gone!
The drawback of this method, and those like it, is that the white pixels are really still there. [more...]
You'll still have to resort to more involved methods like advanced channel magic and Select > Colour Range... if you want to make selections (subjects I'll explore below).


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