You're Smarter Than Your Camera - ISO - How Can I be Sure That Image is Correctly Exposed!!!

May 15, 2015  •  Leave a Comment
You're Smarter Than Your Camera - ISO - How Can I be Sure That Image is Correctly Exposed!!!
Good morning and welcome to the 11th blog on 'You're Smarter Than Your Camera'.  We are continuing with ISO and more specifically how to determine if your image is correctly exposed.  Sometimes it is very hard to see how things look in the small LCD screen at the back of your camera.  In bright sunlight, you can hardly see that little image at all, so unless you plan on tethering a laptop or iPad to your camera (I thought we were trying to reduce the amount of kit we have to carry around :-)) and checking the exposure on that, it is time well spent to learn a little about the tools that your camera has to help with checking your image.

Enjoy and do try to get out and have a go with using these tools, they can be the difference between having an image you can use or nothing at all.

Enjoy your week.

Tracey
So What are the Options

I choose this week to get a little off track from ISO and tell you about these useful tools on your camera, because we are still covering this essential element of photography 'exposure'.  Remember from last week ISO is the third and final variable you have to correctly expose your image without additional tools such as filters or flashes.  It is the option that we adjust last and only, if aperture and shutter speed adjustments can't give us the exposure we want for our image.

There are a few tools that help decode the exposure of image you take other than just the image showing in your LCD screen.  The first one is to switch on highlights on the 'Display Mode' - this will result in flashing elements in your image on the LCD screen where the image has been overexposed.  See the two images below showing my LCD screen of an image I shot which was overexposed.  The image in the LCD screen flashes black and white to indicate that area that has been overexposed.
The Histogram

The histogram is very useful for understanding the exposure of your image. It is a graphical representation of your image.  There are actually two types of histogram - luminance and color.  Luminance is the one we are most interested in and represents the 'brightness' of your image.  The graph represents the entire 'tonal' range that your camera is able to capture from the whitest whites to the blackest blacks.  The left side represents blacks and the right the whites.  The range of the peak represents the number of pixels that contain those 'luminance' levels in your image.

Take a look at my images of my LCD screen below.  I started with an image that is way overexposed.  Notice the shape of the graph that represents the image - all of the peaks are located at the right hand side of the graph.  I then increased my shutter speed and thus reduced the exposure of the image and continued until my image was way underexposed.  Notice how the graph on the overexposed image is skewed all the way to the right and there is quite a bit of the image that is overexposed so much that it is 'blown out'.  This is the furthest to the right on the graph and represents that part of the image that cannot be recovered by any processing - i.e all the detail is lost.  This happens at the other end of the scale as well and has exactly the same effect in that the camera isn't able to determine any detail in the underexposed section of the image. 
Notice in this histogram above, there is a representation of many luminosity levels across the image, but in the histograms below, the image is very simple - just a sample piece of shade and the luminosity representation is very limited. 
Using this simple tool and having it display when you are previewing your images can quickly give you the information you need to decide if you have a correctly exposed image or if you need to retake your shot.
Your Challenge

Treat yourself to taking some images that you have been wanting to capture - spring flowers, events etc.  Use the histogram to determine if your exposure is correct. Try determining if you are capturing an image with a lot of different luminosity levels or just a few.     
Next Time

Thats it for this week...a short but sweet little ditty...next week we will get back to ISO and summarise the three elements that affect exposure as well as introduce the exposure trianble.  I will go deeper into image noise and when it occurs.  There are also different types of noise and some methods we can use during the digital processing to reduce the noise. So tune in to next week and get to grips with controlling noise in your images.

Until then, thanks for reading and enjoy your photography :-)
As always, I would love to hear any comments or questions you have.
Thanks again,
Tracey
 
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References
 
www.wikipedia.org
Complete Guide to Digitial Photography by Rick Sammon
www.cambridgeincolour.com
www.imagemaven.com
www.luminous-landscape.com
www.nikonusa.com 
www.digital-photography-school.com
www.photographylife.com
www.improvephotography.com
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