PDA

View Full Version : Alpha masking scans in Gimp and PS



Jaxilon
01-26-2011, 03:07 PM
I figured something out, oh, I don't know about a month ago, that I should have known about a year ago. I wouldn't say anything except it might help someone else coming along the same path.

If you use a scanner to import your drawings you always have that annoying white background that isn't much help. Personally, I like to strip all my lines off of that background and put them on their own transparent layer. This used to involve me trying to select all the white areas and delete them. That always left a bit of white fuzz around the actual pencil lines. I was left with having to delete by hand or use the grow tool and shave off portions of my sketch. Alas, what a noob!

'Color to Alpha' is your friend. Now it may have been explained at some point but I missed it until I stumbled upon it. By selecting "Colors>Color to Alpha..." you can strip out every bit of white that is left over from your scan. It's very clean and does a wonderful job especially if you have already tweaked the contrast of your image. If you had other colors you wanted to be rid as well, just select the proper color within the "Color to Alpha" pop-up and bang, you are done.

It makes me wonder what else I'm doing the hard way. Sheesh!!

jtougas
01-26-2011, 03:09 PM
Brilliant. :)

Jaxilon
01-26-2011, 03:10 PM
LOL, I feel like an idiot but oh well. If you can't laugh at yourself you deserve the ulcer coming your way.

Gidde
01-26-2011, 03:29 PM
if you don't want to actually delete the white, you can also just change that layer's mode to multiply, or grain merge will increase the contrast but still let you see through the scan. Thanks for posting; it took me awhile
to figure that out when i started as well, and i'm sure we're not the only ones :)

Ghostman
01-26-2011, 03:30 PM
Alternatively you could just set the layer blend mode to 'Multiply'.

EDIT: Ninja'd by Gidde!

Gidde
01-26-2011, 04:34 PM
Mwahahahahaha.

Hai-Etlik
01-27-2011, 03:00 AM
My preferred method is to use inverse of the image as a layer mask.

Jaxilon
01-27-2011, 03:20 AM
All this just goes to show, there is more than one way to skin a layer. :) da-da-dunt

ravells
01-27-2011, 05:51 AM
My preferred method is to use inverse of the image as a layer mask.

OMG that's genius!!! So simple and it never occurred to me and I've never seen it suggested anywhere in 9 years of using photoshop! Then all you need to do is merge the masked image with a transparent layer below to 'commit' the transparency.

I'm going to beat you with my rep stick till you die, Hai-Etlik!!!

Hai-Etlik
01-27-2011, 07:53 AM
OMG that's genius!!! So simple and it never occurred to me and I've never seen it suggested anywhere in 9 years of using photoshop! Then all you need to do is merge the masked image with a transparent layer below to 'commit' the transparency.

I like to leave it as a mask in case I wanted to say recolour or otherwise edit the lines. That's the primary reason I favour it over using multiply.

Gidde
01-27-2011, 09:55 AM
We should change the title of this thread to "how to make a scanned layer transparent" or something and move it to the tut section.

ravells
01-27-2011, 11:52 AM
Good idea, Gidde - done!

RobA
01-27-2011, 04:01 PM
My preferred method is to use inverse of the image as a layer mask.

That is also the easiest way to turn a B&W image into a mono-tint. After creating the layer mask flood fill the layer with a desired colour.

-Rob A>

Sarsaparilla
01-27-2011, 10:46 PM
I figured something out, oh, I don't know about a month ago, that I should have known about a year ago. I wouldn't say anything except it might help someone else coming along the same path.

I can tell you that I didn't know about this until I read your post and it has already helped me.

One further note: while experimenting with removing the background from color images, I discovered that the "Color to Alpha" filter was making the foreground partially transparent, which was not good for my purposes. After some experimentation and some googling, I discovered that the same filter can be applied with a brush for a more precise application. Select the paintbrush tool, and then from the Mode dropdown, choose "Color Erase."

It makes me wonder how many other features I'm overlooking.

RobA
01-27-2011, 10:56 PM
I can tell you that I didn't know about this until I read your post and it has already helped me.

One further note: while experimenting with removing the background from color images, I discovered that the "Color to Alpha" filter was making the foreground partially transparent, which was not good for my purposes. After some experimentation and some googling, I discovered that the same filter can be applied with a brush for a more precise application. Select the paintbrush tool, and then from the Mode dropdown, choose "Color Erase."

It makes me wonder how many other features I'm overlooking.

it doesn't actually make the foreground transparent, but it will make components that match transparent by the degree they match. So if you have a greyscale image then do a colour to transparent and pick white, they grey that has 50% white gets turned into black that is 50% transparent....

-Rob A>

Sarsaparilla
01-27-2011, 11:26 PM
To be more clear: in the specific case I was working with, the paper color was too similar to the parts I wanted to keep, and therefore it was making my image too transparent (and also altering the color balance.) But I bet that result is fairly common any time someone is working with an image that isn't completely black and white.

I tried masking with a selection before applying the filter, but the results weren't satisfactory. The paintbrush version seems to help.