Focus on Photos – ISO!

Wednesday, January 25, 2012

Hello everyone!  Beckie here again, bringing you a little bit o’ photography goodness today :)  I figure it’s time we tackle that photography topic that makes even seasoned photographers shake in their boots…er, I mean high heels…ISO!

A long, long time ago on the blog I did a very basic primer on photography and understanding how ISO, Shutter Speed, and aperture (that f number) work together to capture light to expose an image.  The basic idea is that you want to set those three variables in such a way that your camera meter reads “0″, or it’s perfectly centered between positive (too much light), and negative (not enough light).

ISO is something that many beginning photographers don’t like to utilize in high ranges because either a) they’ve tried a high ISO photo and it didn’t turn out well (lots of noise), or b) they’ve heard from people not to use higher ISOs because their photo will be noisy!  Well, let’s demystify and debunk some of that today!

What I’ve learned about ISO:

1.  It is true that as you increase ISO, you begin to add “noise” to a photo.  How much noise is added and when the noise is introduced (at what ISO range) is somewhat camera dependent.  However, there are things you can do to mitigate noise!

2.  Not all noise is bad.  Seriously.  It’s far better to CAPTURE the moment at a high ISO than to not capture the moment for fear of an imperfect image.  Heck, all the photos from my childhood are either orange, polariods, or glued down into an album that has a plastic cover stuck to it.  So really, put it into perspective – is a tiny bit of noise in an image going to ruin it for future generations?  um…nope.

3.  There are steps you can take to make the noise as minimal as possible.  Let’s look at some of them next!

But first…what is noise?

That, my friends, is noise.  This is a section of a really crappy photo, one shot at a pretty high ISO (ISO3200) that I under-exposed on purpose to exaggerate the noise. I also picked the worst part of the entire image to show you because you can see both types of noise…regular old noise (grainy chunky pixels that shouldn’t be there) and color noise  (colors that don’t belong there – the flecks of pinks, greens, reds, etc that you see around this sample).

Typically you’ll get regular old noise in whiter, lighter portions of an image with the addition of color noise in the darker, shadowed areas.  In this particular example, because it’s that bad, there’s also color noise over the white portion as well.

So…what can you do to prevent un-necessary noise??

NO MATTER WHAT, UNDER ANY CIRCUMSTANCES, SHOULD YOU UNDER-EXPOSE THE PHOTO.

That’s pretty much it :)

In fact, I’d go so far as to say that you actually should learn that you often have to over expose an image to capture it correctly. Slight over exposure is very easy to fix in editing software with simple sliders in  ACR, Lightroom, even Photoshop (here’s a post that covers basic adjustments in ACR).  And over exposing minimizes noise.

Another key reason why you need to over expose in many cases is that, well, the camera meter can be wrong. Well, it’s basically a computer so it’s never really wrong, but it can definitely tell you that something is “right” when it really isn’t.  There are two main reasons this happens:

1. Your metering mode.  I always shoot in spot meter mode because it takes a small, very specific portion of the image into consideration when it determines whether or not there is sufficient light.  Canon cameras use the area just around the center focal point and evaluate the light to give you a meter reading.   An alternative mode, called evaluative, considers a much larger area of the photo around that center focal point and gives you an “average” value for the entire area considered.  I typically photograph people – my kids – and I want their sweet little faces to be properly exposed.  Because of this, I want the camera to disregard everything around them and make sure the photo is exposed properly for their faces.  So I put the center focal point on their faces, adjust the ISO, aperture, and shutter speed until my meter says “0″, and then I shoot.

In evaluative mode, the area around that sweet little face is considered as well.  So if you have strong backlighting your meter will actually consider some of that brightness and determine that your average light value is higher than what it would get as spot metering on the face alone.  As a result the face will come out darker.  You can find many resources on-line to further (better?!) explain these modes, including your camera manual, but for now stick to spot or partial metering (partial metering is kind of in-between spot and evaluative).

2.  The color of your subject.  This one is really, really important so I’m illustrating it below.  Your camera is designed to give you a meter reading as if you are taking a photograph of middle gray (18% gray).  White reflects nearly 100% of light, black reflects nearly 0% of light, and middle gray is – you guessed it – in the middle.  But the world, fortunately, is not shades of gray.  Here’s a very common example/problem…WHITE.

In the series of photos below, I used spot metering and metered off the large white flower hanging down to your left.

In the far left image, my camera meter said I had the perfect amount of light to capture my image – assuming I was taking a photo of something 18% gray!  But I wasn’t…i was taking a photo of red and white flowers.

So – to prove my point – I changed my shutter speed, kept everything else the same, and took another photo when my meter was to the first dot past “0″.  This is called over exposing by 1/3 stop.  That image is brighter overall, and looks better than the one on the left.  I continued this, reducing my shutter speed to add 1/3 of a stop each time, until by the fourth photo I was one full stop over-exposed (according to my meter!).

The FOURTH shot is the best!  Want to know why?

This screen shot says it all.  My histogram shows that very little data in the image is blown (hitting up against the right wall of the histogram), and the portion that is blown is highlighted in bright red in the image itself.  It’s all stuff I don’t care about!  the back lighting in the window, the bright parts of the reflection on the floor…I’m far more satisfied having the flowers nice and bright even though some of the other portions of the image are blown.

Even if this post wasn’t about shooting at high ISO, it’s really important to know that a good SOOC (straight out of camera) image looks more like the photo on the right than the one on the left.  I could scrap this photo as-is without having to do a single thing to it!  Heck, if I really loved it (which I don’t, LOL), I could print it for my wall and hang it up.  Learning to master white balance and exposure in camera, without relying on editing, is the single most important thing for a photographer to accomplish :)

ok – so now we’re ready to tie this back in to ISO…

Here’s a close-up of the noise from the first and fourth images from the exposure sample above:

The general brightness is just much better in the image on the right, but if you look more closely you can see a few other differences.  The image on the left has color  noise on the bottom portion of the white flower while the image on the right doesn’t.  Also, the noise is much heavier, almost “bigger” looking in the neutral space behind the flowers in the image on the left.  The +1 stop photo has much finer, smaller noise.  And keep in mind – ALL of these images were shot with ISO3200, a relatively high ISO setting!

So – wrapping this up (you’re quite a trooper if you’re still with me, LOL!)…

1. PROPERLY expose your photos.  That sometimes means “overexposing”.

2.  Do not sharpen images with noise – it makes it SIGNIFICANTLY worse. I usually fix noise and then do some sharpening if it’s necessary, but they two kind of counter-act each other to watch closely as you make adjustments.

3.  Learn to use noise reduction in your editing software.  ACR has it, as does LR.  I regularly use the noise sliders in LR to reduce noise.  It’s so powerful, in fact, that it can virtually eliminate the noise altogether.   Here’s a before and after with noise reduction applied:

{After settings in the LightRoom noise reduction panel:  Color +18, Luminance +28).

4.  and final…do your own ISO test so that you know how high  you can go with your ISO with confidence.  Do a test just like I did here!

That’s all I have for you today!  Please don’t hesitate to ask questions or to share your own experiences in the comments section!

Join SP tomorrow for the launch of Project SCRAP 2012! Yay!

BeckiePhotography, Uncategorized 8 Comments