Smoothing image noise in layers
Image noise can compromise the level of detail in your digital photos, so reducing this noise can greatly enhance your final image or print. The problem is that most techniques to reduce or remove noise usually end up softening the image as well.
Disturbance signals
Photos shot at dusk are often covered in bright disturbance pixels. They demand a long exposure period or high ISO values to ensure they are sufficiently exposed. Because of this the latent electrical voltage on the sensor is intensified in such a way that the signal is evaluated as image information. This can be annoying as these bright dots cover all the details that disappear in the glare and can no longer be differentiated. At an ISO sensitivity of 1,600, for example, the appearance of digital noise cannot be avoided.
Solutions
Where the picture signal input is too weak the normal sensor signals will appear, especially when its sensitivity is increased.
It is possible to avoid the problem by using a flash. But many photographers prefer natural remainder light, even if there is only very little of it. Our tips will give you the advantage of both: take your image with the available light and avoid image noise. However, this digital trick only works with static photographs such as still life images, landscapes or architectural images. For moving images you need to use corrective filters as an alternative. This kind of application does, however, give a certain level of soft focus that can cause many fine details to be lost.
Initial material
Perfect results can only be achieved with this method if it contains the relevant initial material. Instead of one photo with digital noise, it requires several examples with noise that are then combined. The idea behind it is simple: the disturbance pixels are distributed randomly on each picture, but the image and its outlines remain the same. By combining them, each individual picture contributes its perfect detail and the noise averages out and is cancelled. The more photos that are combined, the more the desired information is added disturbances reduced.
In a pile of pictures the noise can disappear in the average image.
In order for the trick to work the images must be as similar as possible. Even small discrepancies can reduce the focus in the combined photo, as the individual contours are no longer overlapping one another. This makes it very difficult to carry out the process without a tripod. The reward for this hard work, however, is images that are exposed deep into the background, that do not require a bright flash and show no disturbance.
Uniting all the layers
This is done using a tripod and taking a series of around ten photos that are sufficiently exposed because of slow shutter speeds or a high sensitivity setting. We recommend using a remote shutter release so that no shocks occur. You are, however, not so much at risk with a combined rangefinder camera as you are with a reflex camera as there is no mirror to swing back when the picture is taken.
On the smooth area of an evening sky, for example, the colourful noise would certainly be visible. These images, which are failures individually, can now be processed by an image processing programme that can work with layers - for example Photoshop, The Gimp or Paintshop Pro.
Each photo was given its own layer in Photoshop.
All the photos are combined in a single file. As this file can be made up of several layers, the photos can be stacked within it. You first select one with the keys CTRL and a CTRL and C copies it. You then add the photos with CTRL and v to any other image that forms the lowest layer. As you can see in the screenshot, the copy should appear as a new addition in the layer pallet. You copy the other photos into the initial image in the same way so that they are all on top of one another like a thick sandwich.
Precise stacking
When so many photos are stacked on top of one another, it is always possible that a less focused image will sneak its way in. However, there is a simple trick to help you locate it easily. This guarantees that only photos with an exact fit can be stacked to ensure you achieve a perfect result. Here's how it's done:
The layer characteristic 'difference' uncovers differentials. If the image
stays black then the images have identical coverage.
First, click away all the eye symbols from the layer pallet so that all the photos are visible down to the bottom one. This level serves as a reference for the others. You give the images above it the characteristic 'difference' and then make them visible again with the eye symbol. In this mode, only those pixels are shown that do not align in colour and position. In the best case, both layers are basically identical and the picture stays black. Then you can make the layer invisible again and go one layer up. Here too, you activate the eye and give it the characteristic 'difference'.
Removing white contours
You can shift the images so that contours overlap each other once more.
In the event that a photo shows differences as white contours then you can try to remove them by shifting the image. In order to do this you take the movement tool and place it several pixels away until the white edges disappear. As the mouse does not work finely enough for this you control the movement with the four arrow keys that move the layer one pixel at a time. If it cannot be corrected, then you should delete it.
At last - no more noise
If all layers are located correctly you can give back the characteristic 'normal'. The coverage regulator is responsible for the rest of the work; it is located next to the characteristics menu. Each layer is given a different value, in decreasing order. The lowest layer is left on the setting '100 %'. After this, you divide 100 by the layer number. That means the second layer above it is given the coverage 100/2, i.e. 50 per cent, the third 100/3, i.e. 33 per cent. Carry on like this up to the top layer.
Finally, you can combine all the layers with one another. In Photoshop, for example, you select the menu item 'layer - reduce to background layer'. You do need to jump between layers a lot with this technique but the results make it worthwhile.
With varying coverage each photo plays its part in putting digital noise in relation.
In this kind of combined package the digital noise disappears almost completely. Apart from the optical improvements it also increases the range of possibilities for the photographer. Demanding images can be taken without a flash, even in difficult lighting conditions - even beyond the range of the flash, without bright reflections and with the best possible shading.