Removing Noise

Removing Noise

Image editors may feature a number of algorithms which can add or remove noise in an image. JPEG artifacts can be removed; dust and scratches can be removed and an image can be de-speckled. Noise removal merely estimates the state of the scene without the noise and is not a substitute for obtaining a “cleaner” image. Excessive noise reduction leads to a loss of detail, and its application is hence subject to a trade-off between the undesirability of the noise itself and that of the reduction artifacts.

Noise tends to invade images when pictures are taken in low light settings. A new picture can be given an ‘antiquated’ effect by adding uniform monochrome noise.

Here is an example to clear the concept:

 I have taken an image of a great monument of India – The TajMahal. First of all, you have to make one duplicate layer using Layer menu bar – Choose Layer > Duplicate Layer.  Now you change the general effect modes for the layers from Normal to Color.  As we are about to filter color noise, only color changes will affect the general effect of the layers. Make sure the upper layer is selected.

Now comes the most important part of it. Click Filter  > Blur > Gaussian Blur to blur this layer. Set a medium value for Radius. The higher the value, the stronger the noise filtering, and the duller the colors become. The lower the value, the more natural the color effect looks, and the smaller the degree of noise filtering. The value is also affected by the size of the photo and the extent of visible noise. A value of 5 to 10 is usually enough. You can specify higher values if the noise is more obstinate, but for weaker effects, even a value under 5 can be enough. You can see the result on the original picture if Preview is selected.

Most of the time, the procedure makes colors duller, but you can help this by slightly increasing saturation - Click Image > Adjustments > Hue > Saturation.

 Now, you can easily spot the result of filtering now.