Any idea for improving this

Message-ID:<eb0ac767-b728-485f-9fc8-2ae8e6a92d4d@r38g2000yqn.googlegroups.com>
Subject:

Any idea for improving this ?

Date:Sat, 22 Aug 2009 13:07:03 +0100


http://upload.wikimedia.org/wikipedia/commons/6/6e/Pieter_Bruegel_I-Fall_of_rebel_Angels_IMG_1444.JPG

Imho, there is a bit too much "noise", and it is slightly
unsharp ... ? but i would like to make the best of it.

Any suggestions ?

thx,

L

Message-ID:<j7Vjm.322$FV4.296@nwrddc01.gnilink.net>
Subject:

Re: Any idea for improving this ?

Date:Sat, 22 Aug 2009 17:35:27 +0100

lisztfr wrote:
> http://upload.wikimedia.org/wikipedia/commons/6/6e/Pieter_Bruegel_I-Fall_of_rebel_Angels_IMG_1444.JPG
> 
> Imho, there is a bit too much "noise", and it is slightly
> unsharp ... ? but i would like to make the best of it.
> 
> Any suggestions ?

The picture is pretty noisy. I can improve it some, but nowhere to near 
perfection. Here's the basic approach:

1. Selectively apply Gaussian blurring to reduce noise but avoid 
softening edges that are part of the picture.

2. Limit the blurring effect of step 1 to only darker parts of the 
picture, which has the most severe noise problems.

Here're the detailed steps I tried in an experiment:

1. Name layer for the original picture "Original".

2. Duplicate the "Original" layer; name the copy "Overlay". ("Overlay" 
should be above "Original").

(Steps 3 - 12 below apply selective sharpening to a copy of the picture)

3. Make "Overlay" the active layer.

4. Add a layer mask to "Overlay". Use "grayscale copy of layer" for the 
mask.

5. Select the layer mask of "Overlay" for editing. (In the rest of the 
steps here, "the layer mask" refers to that of the "Overlay" layer.)

6. Apply edge detection to the layer mask. (Filters->Edge 
Detect->Edge...; Algorithm = Sobel, Amount = 1.5, "Smear")

7. Apply thresholding to the layer mask. (Colors->Threshold...; 
threshold = 204, meaning pixel values below 204 becomes 0)

8. Apply Gaussian blurring to the layer mask. (Filters->Blur->Gaussian 
Blur...; Horiz. & vert. blur radius = 3.0 px, method = RLE)

9. Invert the layer mask. (Colors->Invert)

10. Select the image (not the layer mask) of "Overlay" layer for editing.

11. Apply Gaussian blur to the "Overlay" image. (Filters->Blur->Gaussian 
Blur...; Horiz. & vert. blur radius = 3.0 px, method = RLE)

12. Apply the layer mask of the "Overlay" layer. (Layer->Mask->Apply 
Layer Mask...)

(Steps 13 - 16 limit the blurring effect only to the darker parts of the 
picture, which can benefit from it.)

13. Add a layer mask to "Overlay". Use "grayscale copy of layer" for the 
mask.

14. Select the layer mask for editing.

15. Invert the layer mask.

16. Use the curve tool to exaggerate the contrast in of layer mask. 
(Colors->Curves...; add control points at (3/8, 1/8) and (6/8, 7/8) for 
the purpose.)

17. Flatten the picture, if desired.

Message-ID:<gtbkm.487$FV4.117@nwrddc01.gnilink.net>
Subject:

Re: Any idea for improving this ?

Date:Sun, 23 Aug 2009 14:27:40 +0100

nesredep egrob wrote:
> On Sat, 22 Aug 2009 16:35:27 GMT, Ricky Rudolph <a@b.c> wrote:
> 
> I have also had a look at that - I do not get 
> 
> "16. Use the curve tool to exaggerate the contrast in of layer mask. 
> (Colors->Curves...; add control points at (3/8, 1/8) and (6/8, 7/8) for 
> the purpose.)"
> 
> Have you got the time to elaborate on this for a newbie, please

The curve tool (found at Colors->Curves...) allows you to remap pixel 
values based on a function defined by a curve. The tool's dialog window 
has a grid that looks somewhat like graph paper. Neither of the vertical 
nor the horizontal axes are labeled. The grid lines are spaced apart by 
about 1/8 of the scale.

When I wrote (3/8, 1/8) and (6/8, 7/8), I was referring to two locations 
on the grid. I was referring to their locations in terms of the coarse 
grid lines. (3/8, 1/8) is my way of say "3/8 of the way from the left 
and 1/8 of the way from the bottom". Likewise (6/8, 7/8) means "6/8 of 
the way from the left and 7/8 of the way from the bottom".

The actual coordinates of these two points on the grid are something 
like (96, 32) and (191, 223) respectively, but I usually just manipulate 
the curve by sight and think in terms of the grid lines.

When you add the above two control points to the curve, you'll define a 
curve of a sigmoid shape (See 
http://en.wikipedia.org/wiki/Sigmoid_function). A curve like that has 
the effect of exaggerating contrast: in the steep rising region of the 
curve, pixel values that were originally close together will be remapped 
to new values that are farther apart.

You can apply the curve tool to either the image in a layer or its layer 
mask. In the step 16 which you asked about, the curve tool is applied to 
the layer mask.