You're Smarter Than Your Camera - ISO - The Exposure Triangle and Unwanted Noise!!!
Good morning and welcome to the 12th blog on 'You're Smarter Than Your Camera'. We are into our final week of ISO and I can't say that I'm sorry to see the end of this topic. It is the poor relative of aperture and shutter speed and really provides for very dry material...so goodbye and good riddance, but not just quite yet. Read on to find a neat summary of the three exposure variables as well as more detail about different types of noise and a couple of short suggestions as to how to reduce it.
Enjoy your week and as always...keep snapping :-)
The Exposure Triangle
Mastering the three elements of exposure is an essential part of understanding your manual camera and taking over control, it also allows you to intuitively use your camera and concentrate on making decisions on other finer elements provided by todays versatile cameras. Aperture, shutter speed and ISO become automatic in your mind and work beautifully together! I know I have gone on a bit about this topic but it is so worth it....and this is just about the last you will hear from me as we are now in the last week of the last variable.
I just wanted to share a great analogy with you - wish I'd thought of it myself, but alas it was on one of my favourite websites - www.cambridgeincolour.com. Try thinking of achieving the correct exposure as similar to collecting rain in a bucket. What are the variables under your control -
- the size of the bucket
- how long you leave it in the rain
- the amount of rain you actually want
The one out of your control is how long and how heavy is the rain and this is very similar to light - natural light anyway.
Take a look at the image below - it is the exposure triangle and show each of the variables and the image result affected by the variable. You can use any combination of the variables to achieve the same exposure, but, the clever bit is knowing which trade-off to make since each setting affects image properties.
If you still feel unfamiliar with this, keep going...it will suddenly click and you will feel like you did in math class when that rotten concept just wasn't going in...and then it did!!!
And onto noise, the digital equivalent of grain in images. Although most of the time it is not desirable, it can provide a vintage or retro look. There will always be some degree on noise in images, the important thing is to have a large signal to noise ratio so that the subject in the image is clearly displayed and the noise is almost invisible.
There are several types of noise created by digital cameras-
Random noise - this is caused by short exposures and high ISOs - the most common and is characterised by intensity and color fluctuations above and below the actual image intensity. The pattern of the noise changes even if the exposure conditions stay the same.
Fixed pattern noise - this usually appears during long exposures. It is characterised by 'hot pixels' which are where the pixel intensity far surpasses that of the ambient random fluctuations described by random noise. It is exacerbated by high temperatures and mostly doesn't change its distribution when the same conditions are repeated.
Banding noise - this type of noise is very camera dependent. It is introduced when the camera reads the image from the sensor. It is most visible at high ISO speeds and in the shadows or where the image has been excessively brightening i.e. perhaps the images was underexposed.
The image above was taken with ISO 200, but the one below, notice all the noise obscuring the detail of the image, it was taken with ISO 25,600. I took the images in good light so even with high ISO, the subject is still clearly recognisable and there are lots of processing options to improve this. During low light conditions, however, noise becomes visible with a much lower ISO - and of course it does depend upon the camera.
More About Noise!
It is interesting to note that with digital cameras noise is most noticeable in darker regions of a camera, but with film, the opposite is true. There are two variations of noise that occur frequently in digital cameras -
- Luminance - where the brightness of pixels is affected and the color is correct. Looks very similar to grain in film images.
- Chrominance - where the correct color is replaced by another. Often blotches of magenta or green occur.
If you are still keen to absorb some more noise information, this article continues with measuring noise statically and uses standard deviation to evaluate the extent of the noise - as usual...from my favourite website :-) - More noise info.
So What can We Do?
I'm not going to go into the detail of removing noise during processing but just to say that there are several programs that do a great job of subtracting the noise from the image without degrading the image. Programs such as Neat Image and Noise Ninja. To begin with you can always try playing with the settings in Photoshop to reduce the noise and the often you can trial these packages free for a period to see what they are capable of. I have tried Noise Ninja and really liked what it can do for the price.
Shoot your images in RAW format allows you to take more control over the editing of your images - more about this in another blog.
Bracketing is another technique that allows you to take several images of the same subject with varying exposures. You can then layer these during processing and eliminate noise - more about this technique in another blog as well.
Last chance to get out there and off auto and shoot with manual to get to grips with the 3 way wonder - aperture, shutter speed and ISO - go on....test the limits and i'd love to see what results you get!
Bye bye ISO and hello white balance and use of different coloured lights. Lets add a bit of color to our images...tune in May for more fun and photography tips.
Until then, thanks for reading and enjoy your photography :-)
As always, I would love to hear any comments or questions you have.