Computer Graphics with Photoshop - Need help with polka dots..

Author

Need help with polka dots..

liaM

2007-10-04, 6:14 pm

I'm stumped by the following problem : the photo consists of a yellow
background to hundreds of green and blue polka dots ; how can I make all
of the green polka dots disappear into the yellow background (while
keeping the blue polka dots intact) ?

How to do this in one go, and not having to erase the dots one by one ?

PS. I use Photoshop 5

Tom Nelson

2007-10-04, 6:14 pm

I love this question! My answer works best if yellow, green and blue
are flat colors with hard edges.

1. Image>Mode>Lab color

2. Window>Channels to view the Channels palette. Drag the "a" channel
to the new-channel icon (page with a corner turned up). A new channel
"a copy" appears at the bottom of the stack and the image changes.
Green is dark gray, blue is light gray, yellow is in between.

3. Image>Adjustments>Levels. The histogram (the picture in the middle)
shows three spikes. Drag the left (black) triangle to the right past
the leftmost spike and the right (white) triangle to the left beyond
the middle spike. The channel shows white everywhere except the green
polka dots, which are black.

4. Click the label "Lab" at the top of the Channels palette. The
display shows your colored image again.

5. Image>Mode>RGB

6. Select>Load Selection>"a copy". Click the "invert" checkbox.
Marching ants surround the green polka dots.

7. The selection might be missing the edge of the polka dots.
Select>Modify>Expand and choose 1 or 2 pixels. The marching ants expand
a tiny bit.

8. With the Eyedropper tool, select the yellow background color.
Edit>Fill>Use: foreground color. The green dots become yellow.

9. Select>Deselect. Done!

Tom Nelson
Tom Nelson Photography

In article <4704d0cd$0$25944$ba4acef3@news.orange.fr>, liaM
<cuddly@mindless.com> wrote:

> I'm stumped by the following problem : the photo consists of a yellow
> background to hundreds of green and blue polka dots ; how can I make all
> of the green polka dots disappear into the yellow background (while
> keeping the blue polka dots intact) ?
>
> How to do this in one go, and not having to erase the dots one by one ?
>
> PS. I use Photoshop 5

liaM

2007-10-04, 6:14 pm

Hello Tom

Glad to meet a connaisseur who recognizes a good question, since I
formulated just so, fancifully, to catch the eye of an expert
connaisseur just like yourself !

Having culled the answers from 4 newsgroups, I find myself in even
more of a bind. My version of Photoshop 5 is in French and the words
don't match. I still have to find what a "channel" is. Secondly,
my formulation of the problem as involving polka dots was not as
appropriate as I thought to the real problem. I am a musician and I need
to erase fingerings and bow markings left on the score by another
musician, which make the music very hard to read. The markings are in a
slightly greenish tint.

Here is a link where a 100 KByte jpeg of the music can be loaded

http://cjoint.com/?kepInSOSUM

I'll greatly appreciate your thoughts on this problem. Meanwhile,
I'll start digging into my french photoshop book and see if I can
spot what a channel is. Does Photoshop version 5 have channels ;) ??

Tom Nelson wrote:[color=darkred]
> I love this question! My answer works best if yellow, green and blue
> are flat colors with hard edges.
>
> 1. Image>Mode>Lab color
>
> 2. Window>Channels to view the Channels palette. Drag the "a" channel
> to the new-channel icon (page with a corner turned up). A new channel
> "a copy" appears at the bottom of the stack and the image changes.
> Green is dark gray, blue is light gray, yellow is in between.
>
> 3. Image>Adjustments>Levels. The histogram (the picture in the middle)
> shows three spikes. Drag the left (black) triangle to the right past
> the leftmost spike and the right (white) triangle to the left beyond
> the middle spike. The channel shows white everywhere except the green
> polka dots, which are black.
>
> 4. Click the label "Lab" at the top of the Channels palette. The
> display shows your colored image again.
>
> 5. Image>Mode>RGB
>
> 6. Select>Load Selection>"a copy". Click the "invert" checkbox.
> Marching ants surround the green polka dots.
>
> 7. The selection might be missing the edge of the polka dots.
> Select>Modify>Expand and choose 1 or 2 pixels. The marching ants expand
> a tiny bit.
>
> 8. With the Eyedropper tool, select the yellow background color.
> Edit>Fill>Use: foreground color. The green dots become yellow.
>
> 9. Select>Deselect. Done!
>
> Tom Nelson
> Tom Nelson Photography
>
> In article <4704d0cd$0$25944$ba4acef3@news.orange.fr>, liaM
> <cuddly@mindless.com> wrote:
>

liaM

2007-10-04, 10:14 pm

Finally understood "channels" = "calques" in French (in english, vellum,
paper semi transparent)

Followed your instructions and learned a whole lot about Photoshop..
especially that there is a lot more to learn and learn by doing.

Thanks.

All things not being equal, I've chosen the following routine for
cleaning up the greenish pencil marks on the music.
(1) work with contrast and range of greys to turn all that is
not black-black in to white.
(2) use the eraser to eliminate the remaining smudges.

Best regards.

KatWoman

2007-10-04, 10:14 pm

"liaM" <cuddly@mindless.com> wrote in message
news:47056692$0$25947$ba4acef3@news.orange.fr...
> Finally understood "channels" = "calques" in French (in english, vellum,
> paper semi transparent)
>
> Followed your instructions and learned a whole lot about Photoshop..
> especially that there is a lot more to learn and learn by doing.
>
> Thanks.
>
> All things not being equal, I've chosen the following routine for
> cleaning up the greenish pencil marks on the music.
> (1) work with contrast and range of greys to turn all that is
> not black-black in to white.
> (2) use the eraser to eliminate the remaining smudges.
>
> Best regards.

yes and that image is not of polka dots
or yellow green and blue

these are polka dots
http://www.wholesalequiltbatting.co.../polka_dots.jpg

music notes on yellowed paper with pencil writing and some smudges is the
correct description of what you posted

liaM

2007-10-04, 10:14 pm

KatWoman wrote:
> "liaM" <cuddly@mindless.com> wrote in message
> news:47056692$0$25947$ba4acef3@news.orange.fr...
>
>
> yes and that image is not of polka dots

note : a polka is a musical piece used to make dots dance :=)

> or yellow green and blue
>
> these are polka dots
> http://www.wholesalequiltbatting.co.../polka_dots.jpg
>
> music notes on yellowed paper with pencil writing and some smudges is the
> correct description of what you posted
>

well.. yeah. But Tom Nelson liked the polka so I have no regrets !

Joe

2007-10-08, 6:14 am

liaM <cuddly@mindless.com> wrote:

<snip>
>
> note : a polka is a musical piece used to make dots dance :=)

I was about to kill file you because your top-posting on other message,
[color=darkred]

And I am glad to see the sample message else I just can't be able to
picture what type of problem you have at your end, and by looking at the
image I can't image why you find an easier way to make thing more
complicate.

- Instead of asking for problem with the Yellow & Green etc.. *WHY* don't
you just pay attention to the SOLID CLEAN BLACK by selecting the BLACK then
discard other colors?

There are several ways so pick one depending on how well you know the
command, and using any combination below.

- Level, adjusting the BLACK = darker and lighter colors = lighter

- Dodge/Burn, you can use dodge/burn to remove the lighter colors

- Color Range, may not work well *but* you can try with FEATHER option which
may smooth the edge.

Also, try the Feather at MENU and feather using Shift-F6 (with combination
of anti-alias) as it may give different result

- Channel, you can use Channel (combination with Level and Dodge/Burn etc.)

But the main thing that you DO NOT want to work on the more difficult part
but learn to find the simplest/easiest part/way to solve the problem. And
BLACK is a good color.