Helicon Filter Help

How to reduce noise selectively

Selective noise reduction is a very powerful feature of Helicon Filter. You can clean noise in some areas and keep details in other areas using such tools as Noise Equalizer, Color Ranges and Reduce noise brush.

As an example we will use a crop from the image that was made with ISO 100 and exposure of 1/320 s (download original image here).

Even with low ISO and short exposure the image demonstrates a quite noticeable noise on the sky.

It gets even worse after we apply some auto contrast and sharpening:

The image above will be our starting point for noise reduction.

Step 1. Open the source image

You can download original image (4Mp, 851K), open it with the usual Open Dialog (menu->File->Open) and apply Auto contrast and Sharpening (threshold=0).

If you would like to experiment with this sample crop, I would suggest you to copy the image from this page and paste it into Helicon Filter with Ctrl-V shortcut.

Step 2. Switch to the Noise tab and apply default settings

Once you've opened the image, switch to the Noise tab and set Enable noise reduction check box.

Default noise reduction is applied to the image and now the result looks like this:

As you can see, the noise on the sky is almost deleted completely . But the texture of the mountains and trees were also affected.

Step 3. Turn on a noise map

It is hight time now to use advanced tools of noise reduction.

Please enable double window mode from the toolbar () of menu (menu->View->Frames->Double).

And enable the noise map by pressing on the appropriate button on the right.

The red color on the noise reduction map shows us that the program will apply noise reduction to all parts of the image. We will try to make the reduction more selective.

Step 4. Use noise equalizer for selective noise reduction

As we would like to clean noise only on the sky, we need to tell the program to process only blue areas and ignore others.

To make this, please turn on the Equalizer and "draw" the following curve:

The curve tells the program to use high (+100%) noise reduction in the blue areas and use low (-100%) noise reduction in all other areas.

Now let's look at the noise map:

The results are much better now. Red color marks the areas where noise should be reduced. We can see only small red spots on the mountain.

Now turn off a noise map, switch to the Save tab to check if you are satisfied with the final image.

For simple cases like this, Equalizer and the Noise map are quick and efficient tools for selective noise reduction. If you would like to get to know about other tools, keep reading this tutorial.

Step 5. Use color ranges for selective noise reduction

Sometimes you need to clean light-blue areas and keep dark-blue areas intact. In such case you cannot use Equalizer as it does not differentiate between dark and light colors. Still Helicon Filter provides you with a necessary tool which is called Color Ranges .

With Color ranges tool you can adjust noise reduction level for each color tint.

To see the effect of Color ranges tool please enable Noise map.

Now, click on the blue sky with the left mouse button. You will see a small popup menu:

Increase noise reduction for the sky and repeat this operation several times. Each command increases the noise reduction level by 50%.

Now, click on the mountain where the details should be preserved. Repeat "Decrease noise reduction" command until the noise map will look like this:

Step 6. Save the resulting image.

If you are contented with your result, switch to Save tab and save the result onto a disk.

	Original image with Auto contrast and Sharpening applied


	The image after selective noise reduction. No noise on the sky, details and textures on the mountain preserved.

If you open the original image later the program will "recall" all parameters that were applied last time. So you will be able to continue editing the original image.

If you have any suggestions for changes to Helicon Filter or to the help and tutorials, please contact us at filter@helicon.com.ua