Computer Graphics with Photoshop

Author

Masking away noise

Léon Obers

2007-06-18, 6:15 pm

Hello,

Editing high ISO digital camera images typically darken areas do contain
more noise than midrange en light areas.

I want to have noise reduction only at more dark areas.
(Smooth and gentle into no noise reduction at more light areas).

Can somebody give a step by step work around how to mask dark areas and
only give noise reduction to the images in dark areas.

Thinking to a workaround maybe using two layers. Background layer give
full noise reduction (e.g. Noise Ninja plugin). Between top layer and
background a mask that shows the dark background region to the top.

I am not experienced enough to have it done in the right way. So please,
a simple step by step explanation.

--
L.O.

Sir F. A. Rien

2007-06-18, 6:15 pm

Léon Obers <mail.to.me@invalid.invalid> found these unused words:

>
>Hello,
>
>Editing high ISO digital camera images typically darken areas do contain
>more noise than midrange en light areas.
>
>I want to have noise reduction only at more dark areas.
>(Smooth and gentle into no noise reduction at more light areas).
>
>Can somebody give a step by step work around how to mask dark areas and
>only give noise reduction to the images in dark areas.
>
>Thinking to a workaround maybe using two layers. Background layer give
>full noise reduction (e.g. Noise Ninja plugin). Between top layer and
>background a mask that shows the dark background region to the top.
>
>I am not experienced enough to have it done in the right way. So please,
>a simple step by step explanation.

Haven't done this as I generally don't use high ISO 'ratings'.

That said, why not select the dark areas, copy and paste to a new layer,
then apply NN to that layer with different settings from the more 'exposed'
layer's portions?

Infinitech

2007-06-18, 6:15 pm

Léon Obers wrote:
> Hello,
>
> Editing high ISO digital camera images typically darken areas do
> contain more noise than midrange en light areas.
>
> I want to have noise reduction only at more dark areas.
> (Smooth and gentle into no noise reduction at more light areas).
>
> Can somebody give a step by step work around how to mask dark areas
> and only give noise reduction to the images in dark areas.
>
> Thinking to a workaround maybe using two layers. Background layer give
> full noise reduction (e.g. Noise Ninja plugin). Between top layer and
> background a mask that shows the dark background region to the top.
>
> I am not experienced enough to have it done in the right way. So
> please, a simple step by step explanation.

you can select with any tool you want the dark areas,
select with a quite wide feather setting
(you don't have to select them precisely)
copy and paste the selection in a new layer,
turn the new layer into "color" mode, apply
1/ anti noise filter if you have PS CS or
2/ just a gaussian blur filter for older PSs,
you can also apply the filter only in a
single channel (red one), and then you
can set opacity of the new layer
to the amount that fit your needs
This is one of the many many ways to do...
If you want to know how
1/select a channel
2/copy and paste a selection
3/select an area
4/change blending modes
etc
etc
all, absolutely all, is written in the help menu :-)
HTH
--
Infinitech

ronviers@gmail.com

2007-06-18, 6:15 pm

Hi L.O.

One way is to add a threshold layer, Layer>New Adjustment
Layer>Threshold, to make your value selections. You can double click
on the threshold layer icon to make new selections. Then use the add
noise filter, Filter>Noise>Add Noise, to increase the noise in the
selected regions.

Good luck,
Ron

Léon Obers

2007-06-20, 6:14 am

Léon Obers wrote:

> Editing high ISO digital camera images typically darken areas do contain
> more noise than midrange en light areas.
>
> I want to have noise reduction only at more dark areas.
> (Smooth and gentle into no noise reduction at more light areas).

Thanks to everybody in giving a suggestion for noise reduction to
particular dark areas. Reading and learning, this is what I finaly found
out myself for more noise reduction in dark areas, less in midrange and
highlight areas.

- image --> select all (Ctrl+A) --> copy the image (Ctrl+C)
- go to the channels section --> create new Alpha channel
- paste the image to the Alpha channel (Ctrl+V)
- invert Alpha channel (Ctrl+I)
- gaussian blur Alpha channel between about 2 to 5 pixels
- curve Alpha channel change whitepoint --> input/output --> 240/255
(or more difference to have maximum noise reduction for more
light "blacks" and dark grays in final image)
+ possible change blackpoint to your liking
(for no noise reduction at all in higlight areas in final image,
e.g. input/output --> 40/0)
- load channel as a selection
- delete Alpha channel (not needed anymore selection is made)
- go to layers section --> copy background layer
- noise reduction (e.g. Neat Image plugin) to background copy
- deselect selection (Ctrl D)
- change opacity background copy to your liking
(for less noise reduction in comparison with background image)
- flatten image

I made an action out of it to have more fast and automatic noise
reduction to many images. The last "flatten" function you can disable
for manual change of opacity for individual image likings before final
result.

--
Vr.groet - regards, Léon Obers