Introduction: Sharp Low-noise Photography Using Multiple Photos

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This is a guide to using multiple shots and photoshop to avoid having to choose between motionblur (handshaking), or loads of noise when shooting badly lit subjects (high ISO sensitivity).
It's (propably) just a way to achieve "digital image stabilisation" using older cameras.
Any camera can be used, but high speed shooting will be preferable.

The image will also have to be cropped afterwards, so there's a slight loss of resolution (and you have to "reframe in photoshop afterwards).

We will be doing all the magic with a nice little feature in Photoshop CS3, under the "Load Images into Stack" script.

Step 1: About Low Quality Pictures

This section is for photography rookies. If you know about shutter speed and the "shaky hands motionblur"-syndrome, then just skip this step.

So, you propably used a camera more than once, and maybe you have noticed, that when outside in the sun, the pictures are most often crisp and sharp, without any ugly noise.

When shooting in low light however, like indoors, you have propably noticed that the picture tends to get blurry and maybe with visible noise. Alot of people tend to believe it is because their camera "sucks", but often, it is because they just do not know the reason why these artifacts occur.

First I will try to explain the blur.

When you take a picture, you expose the sensor in the camera, so that light reflected from the subject, can hit the sensor and be registered as an electrical impulse.
This happens over a period of time. A longer period of exposure lets more light hit the sensor, which gives brighter images.
Unfortunately, during this exposure time, the subject might move compared to the camera.
Logically this will place the object in a new spot on the picture taken.
The object will therefore appear on the final picture both where it was at the start of the exposure, but also where it was at the end.
It will also leave a trace of itself between the two points, and looks transparent because of whatever being behind the subject at the beginning of the exposure, is visible to the camera at the end of the exposure.

For more info on motion blur, see here

The "shaky hands syndrome" is a result of motionblur, but not where the subject moves.
You might think you can hold the camera completely still, but you still move your hands (and the rest of your body) a tiny bit. Might not seam as much, but it will be alot for the camera,
especially if you have zoomed in.
This small movement will create motionblur. Not because the subjects move, but because the camera moves. When you hold your camera "still" your muscles jitter, and your balance shifts slightly, moving the camera slightly in several directions.
This makes it occur as general blurring, like it was out of focus.

The longer exposure times you use, the worse it will get.

Outside in the sun the exposure time (shutter speed) might be 1/125-1/1000 of a second, making the motion blur way too insignificant to be visible.

Inside however, you might only get 1/30, or maybe 1/2 second exposure time. This leaves plenty of room for motion blurring.

Modern cameras on automatic will try to avoid the long shutter speed.
To compensate for the smaller amount of light gathered, it either opens the aperture more, which will let more light through the lens, or, when the aperture can not get any bigger, make the sensor more sensitive.

The image sensor builds up a small charge at each cell depending on the amount of light hitting them. More light, bigger charge, brighter pixel.
(each 4 cells represent a pixel, with each cell registering blue, red, or green light, with the last one being used differently depending on sensor design).

Only problem is that these sensors are not perfect.
Alot of things can increase or decrease the charge at each cell. Temperature, difference in sensitivity between pixels etc. can make a each cell give off a too high or too low charge. This appears as too bright or too dark pixels of different colors on the final image.
The more sensitive the sensor is, the more noise there will be on the final image.

More info on the subject here: http://en.wikipedia.org/wiki/Image_noise

Fortunately for us, the noise pattern changes each time you take a new picture.

Phew! that was alot of work. hope you understood it :) Else, add comment, and I'll try to rephrase something, or add a picture for explanation.

Step 2: Configuring the Camera

So, every time you take a picture, you get some noise.
When shooting dark scenes, and use a high ISO speed (sensor sensitivity) it is very visible,
while it is almost impossible to find on well lit bright pictures.

This noise does not look the same on each photo you take,
so by taking multiple photos, you can just find an average color for the same pixel on each image.
In that way you can get closer to the "actual" color.

So... Find yourself a subject with the right lighting for this experiment. I just chose a bunch of books in my room, lit by 2 windows with an overcast sky outside, right after sundown.

If you have "exposure compensation" on your camera, and don't want to learn how to do this manually, just find the =!= and read on from there.

Make sure your camera is set to "green automatic". Frame your subject and take a shot.
Is the result blurry or noise? Good... Find the info for the newly taken picture on your camera. You need 2 numbers: shutter speed and sensitivity.

First number is often a fraction, like 1/30 or 1/2, or maybe just a whole number, like 1 or 2 (often displayed like 1" or 2") The other number can often be divided with 100 or 25.

Exposure time / shutter speed:

16" 8" 4" 2" 1" 1/2 1/4 1/8 1/16 1/30 1/60 1/125 1/250

ISO speed / sensor sensitivity:

100 200 400 800 1600 3200

Each of these numbers are "full steps". Your camera will step in either 1/2 steps or 1/3 steps.

The numbers can therefore also be for example:

Exposure time:

1,3" or 1,6" between 1" and 2" at 1/3 step, or 1,5" at 1/2 step

125 or 160 between 100 and 200, at 1/3, or 150 at 1/2 step

Now you know what settings will give the right exposure.

We will be combining 8 photos in this instructable, each with 1/8 the needed brightness.
As you have propably noticed, each step on the above scales are either half of, or double of the previous, depending on in which direction you're moving on the list above.
So, we need to step down (go to the right) 3 times. This can be done with either shutter speed, ISO sensitivity, or a combination.

Go for shutter speed as first priority.

Find the "manual" mode on the camera. Dial in the shutter speed and sensitivity found earlier.
Now, step these settings down 3 steps. That is pressing down 9 times if your camera uses 1/3 steps, and 6 times if it's 1/2 steps.

=!=The easy way

Find "exposure compensation" on your camera. If you don't know where to find it, look in the manual.
Set this to "-3 EV" this will take the picture 3 steps lower than what the camera otherwise would find suiting. Here you can not really control the settings, the camera will choose sensitivity and shutter speed.

Step 3: Taking the Pictures

Frame your subject, try to hold the camera as still as you can, and take more than 8 pictures.
Some of the pictures might have a little bit of motion blur, so it's nice to have a few to pick from.

Each picture should be kind of dark like the one below.

Take all the pictures in one run, else your second bunch of pictures might not align well enough with the first, and you'll have to cut alot off at the edges.

Step 4: Combining the Pictures in Photoshop

When you have taken all the pictures, fire up Photoshop, and choose File>Scripts>Load Files into Stack.

Step 5: Load the Pictures Into Photoshop

Press the "Browse..."-button, and find your pictures. Just select all of them if you have more than 8.
You can sort them afterwards.

And now for the small detail, that's gonna make sure that all these pictures align:
before pressing "OK" check the checkbox "Attempt to Automatically Align Source Images"

THEN press "OK" and wait for all the pictures to load in and align.

Step 6: Adjust Layers

Now that you have all the pictures loaded into one file, it's time to sort them.
Delete the most blurry ones untill you have 8 left.

Now, select the layer 2nd from the bottom, and change it from "Normal" to "Screen". This will add the value of each pixel to the value of the pixel on the layer below.

Do this for all the layers above that one.

Step 7: Done! and a Note on Another Method

Now you should have an image with low noise level, and a decent sharpness.
Collapse the layers, and/or crop the image to remove the blank areas that appeared along the edge as a result of the alignment.

... And there you go :) My example hasn't been cropped yet, so you can still see the blank areas.

Another way to do this is to just shoot all the photos with a high ISO sensitivity, combine them in photoshop with the same method, but instead of choosing "screen", use "Lighten" or "Lighter color".
I do not know what these do, but they seam to be the ones getting closest to taking the average color/brightness value of each pixel on each layer, which is the idea here.

EDIT

Instead, keep all layers at "normal" and just change the opacity of each layer to around 20% or something... That will get closer to the actual average.