Histograms Part 6

Now that you are all experts on how to use histograms to evaluate exposure, here are instructions on how to access them on a Nikon D40 (I would guess that the D40x, D60, D3000 and maybe the D5000 are probably about the same.)

After you do this one time, the camera will remember your choices making it a lot easier every other time, so don't get overwhelmed. 

1. Start with a picture displayed on the LCD and press "ok" in the center of the thumb pad. 
2. Toggle down to "filter effects" and press "ok" again.
3. Toggle to "color balance" and press ok

Now you are looking at the three histograms you need to evaluate your exposure. They are being displayed as part of a gimmick-tool used to change the color balance in your picture - which you don't want to use - so be careful that you don't make any changes to the color balance by accidentally moving things around. (If you make a mistake, just press the play button to cancel as it indicates.)

After you've done this once, you won't have to do any toggling on the menus because the camera will remember your previous choices. So all you have to do is press "ok" three times in a row and you're there.

If you have another Nikon camera, there is an easier way (typically) to access the histograms. When you are looking at a picture on your LCD, just press the directional thumb pad on whatever axis you don't use to switch to a different picture. In other words, if you navigate through your images using left and right, you will use up and down to scroll through a few information pages associated with the currently displayed picture. And if you navigate using up and down, you will use left and right to see the information. Just go through those information pages until you see the three colored graphs.

If you have another brand of camera, I'm sorry to say I can't tell you how to access the histograms. But most cameras have them in there somewhere, so dust of your manual to find out how to get to them. 

Using histograms to evaluate exposure is a lot more useful on your camera when you can make an adjustment and take another shot than it would be later on your computer. 

Histograms Part 5

So now we get to it. It may seem obvious at this point what you can do with histograms (if so, great,) but just in case, I'm going to try to explain exactly how to use them.

When you look at a histogram (hopefully a three-color histogram,) you are looking for mountains of data spreading across the graph that don't bump up against the edges of the graph. If you do have a peak or a spike against an edge of the graph, you will be losing information in your file and consequently, texture and contrast in your image. Additionally, you don't want a large space between your data-graph and an edge (the right edge especially.) So here are some examples…

In one of my very first posts on exposure, I gave same ideas to help judge exposure based on what you can see on your camera's LCD. Those judgements are be based on visual cues which lead to an evaluation that is ultimately subjective. I'm going to use those same images, but this time evaluate them objectively using histograms. Here are the images with their corresponding histograms following each:

The above image is underexposed. Even though the graphs are not bumping up against the left edge very much, the fact that there is no information in the right quarter of any of the graphs tells us that this image is underexposed. Very badly underexposed images may have graphs that are more extreme than this, but those will be more obvious without a graph. This type of underexposure is where histograms are really valuable. If you see a graph like this, use exposure compensation to adjust your exposure.

This image is overexposed. You can see in the red channel, that the graph is running into the right edge - this is often the case in overexposed images of people since most skin (black, white or in between) will show up in the red channel. The overexposure of the red channel causes the neon look in the skin (notice the nose in particular.) If you see a graph like this, use exposure compensation to adjust your exposure.

This is properly exposed image. The graphs come right up to the right edge with out running into it. These are the types of graphs you should look for. Here are some other good looking histograms following their corresponding images:

This last one is a curveball - and an important lesson. The histograms are running into the right edge indicating that there is some overexposure. However, this is a properly exposed image of my daughter. What is overexposed is the snow. That is why there are patches of pure white in the snow where you can't see any texture. The only way to save the detail in the snow would be to underexpose my daughter. I didn't do that since, obviously, she is the most important part of the picture.

In many images, there will be decisions like this you will have to make. So don't just depend on histograms without thinking. If you can identify why your graphs are hitting the edges, and your ok with losing that information (like the snow,) then don't worry about it.

Read Part 6 next.

Histograms Part 4

Three Color Histograms
To really use histograms effectively when evaluating exposure, you need to use three-color-histograms. If you understand what I've explained in Part 1, Part 2, and Part 3, this isn't too complicated. We must simply realize that our cameras aren't recording different levels of grey, but actually different levels of red light, green light and blue light. So instead of thinking of brightness levels as the variation between black and white, we must think of them as the variations between dark red and light red, dark green and light green, and dark blue and light blue. If that doesn't make sense, come back a read this paragraph again after you read the rest of this post.

When we look at the three color histogram from the picture in Part 3, we see this:

from this picture

So what you are looking at in the graph above is the variation in brightness of red light, green light, and blue light in the picture. So that's how digital cameras work - they record the variation in red, green, and blue light and then overlay the three one-color images to produce color images. So when we take a picture, we need to make sure that all three graphs stay away from the edges.

Next time we will take all the theory and make it practical and usable.

Read Part 5 next.

Histograms Part 3

Read Part 1 and Part 2 first.

So today we actually get to it. Hopefully, after the last two posts, this principle has become clear: the sensor in a DSLR can only record a limited range of brightness levels in any given scene. Because of that, it would be nice to know how well we are utilizing the different brightness levels that our sensor is able to record. Our effectiveness in using our sensor in this way is all about proper exposure. And the best tool we have to know how well we have exposed a picture is a histogram. So here we go…

As I said in Part 1, a histogram is just a graph that plots data. In digital photography, the data that it plots has to do with brightness levels. The graph basically tells us how many pixels were recorded at each available brightness level. So here's what a histogram looks like:

What you are looking at is a graph with all the different brightness levels the camera could record across the bottom and the number of pixels recorded at each level up the side. Here is the image that this histogram came from:

In this image the available brightness levels are used quite well - this is a well exposed image. The hump on the left of the histogram represents most of the wood and hair while the hump on the right of the histogram represents most of the skin and dress. Here is a color-coded comparison of where the brightness levels are actually distributed:

So you can see the large blue hump represents lots of pixels in the image. Similarly, the green/yellow hump represents a lot of pixels too, but fewer than the blue hump. Obviously there aren't a lot of pixels in the red area, which is why that part of the graph is so low.

When you look at a histogram, a well exposed image will have most of the pixels distributed with the humps away from the edges. If there are humps in the graph up against either edge, you will be losing information. Consider these two pictures from  Part 1 with their corresponding histograms:

Notice how this histogram has a hump on the left representing the blackest parts of the pipe. A wide range of brightness levels that fell below the recordable range are getting assigned the lowest brightness levels. In other words, parts of the pipe that should have been recorded at levels like 0, -1, -2… were all recorded at level 1 since that is the darkest level available. The result is that there is no separation between what differences in brightness there were in real life. So instead of seeing texture in those very dark parts of the pipe, we just see black patches.

In this histogram, notice the spike on the very right edge. This spike represents every pixel in the sky of the image. Even though there were differences in the level of brightness in the sky in real life, they all fell above the range that was recorded and therefore were all assigned the highest brightness level. So in this image, let's say the brightest level is ten. The problem is that the sky has levels 11-15 in it. But since ten is the brightest level that can be recorded, all those pixels were recorded at ten. Again, because there is no difference in the recorded brightness level, there is no detail in that part of the picture.

Ok, so we covered a lot today and actually started talking about histograms. But there is still a lot to cover including how to use this information when you are taking pictures and the importance of three-color-histograms. Like I said in the beginning, this is a complicated subject, but a very, very valuable tool. I hope you stick with it. Let me know if you have questions so far.

Read Part 4 next.

Histograms Part 2

Read Histograms Part 1 first.

As I explained yesterday, our cameras' digital sensors can only record a limited range of brightness values at a given time. Anything that does not fit into that range will show up as either white, if it is brighter than the range, or black, if it is darker than the range. Here is an illustration that I hope will help you to understand this principle.

Imagine that you are working on a paint-by-number picture in gray-scale. You have eight shades from black to white to paint with. When you look at the picture you notice that there are sections numbered from one to ten. Now, you only have eight shades, so you can't paint all ten different shades that are in the picture. You have two choices.

1. You can use your darkest shade as #1 and let anything marked with #8, #9 or #10 all be filled in with your lightest shade.
2. You can use your lightest shade as #10 and let anything marked with #1, #2 or #3 all be filled in with your darkest shade.

Either way, you are going to lose some detail that is supposed to be in your picture. Either the three lightest shades will all be one shade, or the three darkest shades will all be one shade. Look and see . . .

Here is your paint by number picture:

If you had ten shades, it would look like this:

But since you have only eight, you must choose one of the following options:

In the first option, the lighter sky shades are combined so you can't distinguish between the sky, clouds and birds. In the second option, the darker shades are combined so the middle of the flower runs together.

I simplified this picture from yesterday to illustrate this point in a real image:

If my D40 sensor could have recorded more levels, there could have been more detail in the pipe. But anything darker than "1" was all recorded as "1."

I hope this is helping you understand a little bit more about how your camera is working. Please let me know if you have any questions. Ultimately, this knowledge will enable you to judge your exposure much more quickly and accurately. Read Part 3 next.

Histograms Part 1

With this post, I'm in danger of covering a subject that is overly complicated and beyond what photomoms want to know. But I'm going to give it a try anyway, so let me know what you think. Hopefully I can explain it simply enough to be practical and useful.

Introduction
Histograms are graphs that plot data. When used in digital photography these graphs can provide valuable feedback regarding exposure. This feedback is particularly useful because it is objective. It takes a little effort to understand histograms, but once you do, they are quick and easy.

Important Background Information
The sensor in your camera can only record a certain range of brightness values at a given time. That means that if there is too much contrast in a scene, your camera cannot record it all.

It may help to think about your sensor as the paddle in pong. You can move it back and forth from right to left in order to capture a different range of the brightness spectrum, but the paddle can't cover it all. Thankfully, most scenes don't have a "full spectrum" of brightness in this sense, but often the variation in brightness is greater than our sensors can record. Consider these two examples:

In this image I slid my pong-paddle-sensor toward the brighter side of the spectrum so that I could capture my wife and daughter at the other end of this pipe. In doing this, I sacrificed a lot in the darker part of the spectrum. As a result, much of the pipe appears as solid black with no texture.

In this image I sacrificed some of the brighter part of the spectrum so that my daughter wouldn't be too dark. The result is that the sky is pure white without any detail.

If you understand this principle, you are on your way to understanding histograms and using them to your advantage. Read Part 2 next..

White Balance and Mood

If you don't know what white balance is, read here.

White balance is typically used to make the colors in your pictures look accurate.  The goal is to make white things look white and all the other colors look like they do in real life.  However, white balance can also be used to change the mood of your pictures.  Changing the white balance can make pictures seem warmer or cooler (some may say harsher.)

Most of your camera's white balance settings change how blue or orange your image appears.  (The fluorescent setting does not fit in this category since fluorescent lights are greener than other light sources.)  Because of this, intentionally using a WB setting that is not the most accurate can make your picture seem warmer or cooler than it actually was in real life.  Consider the following pictures:

This shot was taken on a gloomy, overcast day.  And it looks like it because the WB was set for cloudy.

This shot was taken a moment later with the WB set to shade.

Notice how much warmer this image looks.  It may not be reality, but it's a nicer picture to look at.  Try experimenting with your WB settings so you know what they do to your pictures.  Then when you want to make a slight color adjustment to you pictures, you can use your WB to do it.

What is White Balance

I covered this topic for point and shoot cameras and the theory is not any different on DSLRs.  But I want to cover it again in case anybody skipped it thinking it was specific instruction for P&S cameras.

White Balance is a function on digital cameras that allows you to influence the color balance of your images. The point is to make colors in your picture look like they do in real life. It's called white balance because it can help make your whites look white, but it really affects the hue of all the colors.

The reason White Balance is important is that different light sources (incandescent light bulbs, fluorescent light bulbs, the sun . . .) produce different colors of light. Our eyes are used to these differences and our brains make adjustments so we can still tell something is white when it has orange light on it. The problem is that when we take a picture under one kind of light and then look at it outside of its context, the colors will look wrong.

If you've never adjusted the white balance (WB) on your camera, it is probably set to auto.  In auto mode, your camera will do a fine job guessing at what kind of light is illuminating your scene most of the time, but sometimes it needs help. If you notice that the colors in your picture are "off" you can help your camera by telling it what kind of light there is.

Here are examples of what WB can do. Notice how the colors are different in each image. FYI, the cloudy setting produced the most accurate colors . . . and it was cloudy when I took the picture.

Info Display on a D40

If you are using a Nikon D40, this should be helpful.  When you press the info button (see two options below) your D40 displays a bunch of information on the LCD screen on the back of the camera.  If you've been following our blog for a while, much of that information may now be relevant to you in a way that it wasn't before.  So when using this information screen here are two things you should know:

• You can change the way the information is displayed between what Nikon calls "Classic," "Graphic," or "Wallpaper."  I would probably call them "useful," "confusing," and "ridiculous," but that's just my opinion and you are free to form your own.  I use the "Classic" view because it is the plainest and makes the most sense to me.  When I press the info button I can see all the settings that I'm regularly interested in.  If you want to see what the different display modes look like press the menu button, go to the "SETUP MENU" (the wrench), and select "Info Display Format."  Then you have two choices which lead to the three selections listed above.  The two choices apply to different shooting modes, but I can't imagine why you would want your information to be displayed differently in different modes.  So I suggest figuring out which display option you like the best and setting it in both places.
• While you have the information screen displayed, you can press the info button on the back (don't ask me why it doesn't work with the info button on the top,) and have direct access to adjusting many of the settings that are displayed on the screen.  Use the directional pad to pick an option and press OK to make changes.  Interestingly, when you enter this adjustment mode, the display assumes the "Classic" view no matter what you have set.  This is a great way to access relevant setting quickly.  You can change the following settings:
• Image Quality
• Image Size
• White Balance
• ISO
• Shooting Mode
• Focus Mode
• AF-area mode
• Metering
• Flash Compensation
• Exposure Compensation
• Flash Mode

How to Control the Flash

When using an on-camera-flash, we rarely achieve even exposure.  Typically one part of the picture is way too bright, or most of the picture is way too dark.  This is because that little flash doesn't light up the whole scene evenly, but instead gives us a spotlight effect like this:

I love this picture, but not because of it's photographic excellence.

One of the important components that contributes to using your on-camera-flash effectively is understanding how to control its power.  If you know how to do this, you can essentially turn your flash up and down to better balance its brightness with other light sources in your picture.

So here's how on the Nikon D40.  (If you are in green-auto mode, forget about it.  You can't control anything.  Switch to P to control your flash . . . but remember, your flash isn't going to pop up unless you push the button.)  Assuming you have popped up your flash you need to hold down the flash release button and the exposure compensation button while winding the command dial.  I've indicated these controls in order in the following images.

As you wind, you will see a number changing in the view finder and a corresponding number changing on the LCD screen.  As with exposure compensation, you will see a 0 change to things like +.3 , +.7 , +1 . . . or -.3 , .-7 , -1 . . . The negative numbers decrease the flash output and the positive numbers increase it.  Remember to change it back when you are done.

Application
So what's the use?  First we must consider when our on-camera-flash is useful in the first place.  It's always there as a last resort as in the picture above, but its real usefulness comes when a small portion of your image needs more light to even out the exposure.  Here's an example:

Elizabeth's face is too dark for the rest of the picture because she is in the shade and the background is in the sun.  I can't very easily darken the background, but I can use the flash to brighten her face.  So I popped up the flash and got this:

Not exactly what I want, so I employed the technique I just described and dialed the flash power down to -1.  I got this:

And this at -2:

The best option would probably be between these two (maybe -1.3 or -1.7,) but hopefully you get the point.  This example shows both a good example of when your flash is useful and also how to use it effectively.

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Expanding the Menu

If you tried to follow along with our Auto-ISO post last week and had some trouble, this might help.

The Nikon D40 has an option in one part of the menu that lets you choose how much you see in another part.  If you are never going to use all the options in the menu this could be a good thing, but if you are trying to set the ISO to auto you will have a problem.

To see all your options in the Custom Settings Menu, follow these steps:

1. Press "Menu" on the back of the camera
2. Navigate to the "Setup Menu" (the wrench) 
3. Select "CSM/Setup menu" and change it to "full."

This will expand the options you can see in the CSM menu.  And now you will be able to see "10 ISO auto."

Auto ISO

ISO is an extremely valuable tool in digital photography.  It's great to be able to adjust the sensitivity of your sensor as the lighting conditions change without having to change an entire roll of film.  But as convenient as it is (especially compared to film,) it would be great if it could be something we never had to think about. That's where the auto ISO setting comes in.

This subject is a little complicated.  To fully appreciate what auto ISO does, you have to understand the advantages and disadvantages of changing ISO as well as the affect shutter speed has on your images.  If this is beyond you right now, keep reading and just use the settings I recommend.  Even if you don't understand it all yet, it will help you get better pictures consistently.  For background, read What is ISO and ISO and Digital Noise as well as How to Choose a Shutter Speed Part One and Two.

Recent Nikon cameras (I don't know for sure about Canon) have an "auto" setting for ISO that allows you to set a range for your ISO and then never think about it again.  That's too strong.  With auto ISO you hardly ever have to think about your ISO setting.  When turned on, auto ISO works by starting at whatever ISO you have set and gradually bumping it up if there isn't enough light in the scene you are photographing.  Additionally, you can set a maximum so that your camera won't take your ISO higher than you are comfortable.

Here is how to set it on a Nikon D40:

1. Push the "MENU" button on the back, navigate to the "Custom Settings Menu" (the pencil), then select "10 ISO auto."  Select "On" and push "OK."
2. Then select "10 ISO auto" again.  This time select "Max. sensitivity" and choose the highest ISO that doesn't produce enough noise to bother you.  (Read ISO and Digital Noise if you need help deciding.  I would choose 800 on the D40.)
3. Then select "10 ISO auto" again.  This time select "Min. shutter speed" and choose the minimum shutter speed that would produce sharp images with your lens.  (Read How to Choose a Shutter Speed Part One and Two if you need help deciding.  I would choose 1/30s or 1/60s depending on the lens.  Choose 1/60s if you have a VR telephoto lens and don't want to ever change your ISO again.)
4. Push the "MENU" button on the back, navigate to the "Shooting Menu" (the camera), then select "ISO sensitivity."  Choose the lowest number there is (200 on the D40, 100 on some other cameras.)  Ignore the "Auto" in this menu - it's not the same thing.

Here's what will happen: your camera will shoot at it's "base ISO" (which you set in step 4) most of the time.  When it's too dark and your shutter speed starts to slow down, it won't go slower than whatever you set in step 3.  Instead, your camera will increase your ISO, but it won't go past the maximum you set in step 2.  This is great because it allows the camera to make the decision you would make without you having to do anything.  You have enough freedom to limit the camera's choices, but you also get to take advantage of your camera's intelligence.

If you can't see "10 ISO auto," read Expanding the Menu.
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How to Focus Your Camera Part Two

The last thing people want to have to do when taking pictures is fiddle with the settings in between each shot.  Therefore, when it comes to focusing, I recommend setting your camera to the options that will be most useful most of the time.  (Read Part One to find out what I think those options are.)

Unfortunately, even the best settings won't work all the time.  If you set your focusing system the way I recommend, there is (at least) one situation that will turn out badly: when your subject is moving quickly toward or away from your camera.  When your camera focuses, it focuses at a certain distance.  If the distance between your camera and your subject changes between the time you focus and the time you take the picture, your subject will be out of focus.

Let me explain this with an example.  In the picture above, my daughter was swinging and so the distance between her and the camera was constantly changing.  With my normal settings I was getting pictures out of focus because as I would push the button, the focus would lock when it got half way down and then the image would be captured when the button was depressed all the way.  She was swinging quickly enough that there was enough time between focusing and capturing the image for the distance to change.

So here is the solution:
When your subject is moving toward or away from your camera (more quickly than walking), set your "Focus Mode" to "Continuous-servo AF" (AF-C).  To do this push the "MENU" button on the back, navigate to the "Custom Settings Menu" (the pencil), then select "02 Focus mode," and highlight "Continuous-servo AF."  In this mode, your camera will continue focusing right up until you take the picture no matter how long you hold the button half-way down.
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How to Focus Your Camera Part One

I talked yesterday about focusing on your subject's eyes when photographing people, so today I want to make sure everyone knows how to dictate where your camera/lens focuses.  (I'll be describing how the Nikon D40 works, but what I say will apply to all current Nikon cameras using the same terms and options.  Other camera brands will undoubtedly have the same features, but possibly with different names.)

Camera Set Up
The first step is making sure your camera is set up correctly to allow you to control the focus.  Here are the steps needed to accomplish this on the D40:

1. Your camera will make all the focusing decisions in AUTO mode, so first put your camera in program mode by winding the dial on top to "P".
2. Change the "AF-area mode" to "Single area." Do this by pushing the "MENU" button on the back, navigate to the "Custom Settings Menu" (the pencil), then select "03 AF-area mode," and make sure "Single area" is highlighted.
3. Start with the "Focus mode" in "Single-servo AF."  Follow the steps above, but select "02 Focus Mode," and choose "Single-servo AF."

Once you have set your camera to these settings, it will focus on one of the three sets of brackets that you see when you peer through the view finder.  As you look through the view finder, you can select which set of brackets is active using the directional pad that encircles the OK button on the back of your camera.  When you push the directional pad, one of the brackets will momentarily light up in red to indicate you have selected that one.

Controlling the Focus

When composing your picture, line up the selected brackets with what you want in focus.  If you want to be able to change the composition (which might take your object of focus out of the brackets,) but still stay focused on the same point, just push your shutter release button half way down and hold it there - this will lock the focus.  Then recompose and push the shutter release the rest of the way down to capture the image.

This may sound complicated, but you will get the hang of it quickly.  Once you understand this, you will probably leave your camera set this way 90% of the time (we'll talk soon about the other 10%), so don't worry about remembering all the menu options.  Just set it and be done with it.  If you have any trouble, or if your camera doesn't have the same menu options contact me or leave a comment.

Read How to Focus Your Camera Part Two next

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How to Choose an ISO

Read background on ISO here and here.

As I've said before, your camera will preform best at its lowest ISO.  Therefore, it is best to set your camera to the lowest ISO setting you can under the conditions you are photographing.  However, there are times when it is valuable, or even essential, to increase your ISO in order to capture a descent image.  Consider this situation . . .

I took this picture at ISO 200 with a shutter speed of 1/2.5 and aperture of f/5.

If you look closely you can see that the picture is blurry because the shutter speed is too slow (see How to choose a Shutter Speed for more on this.)

If I kept all the other settings the same and increased my shutter speed, it would produce a darker image, which is not what I wanted.  Another option (in theory) would be to increase the shutter speed (letting less light in) and make the aperture wider (letting more light in) to produce the same exposure with a faster shutter speed.  Unfortunately, in this situation, the aperture was already as wide as it could go.  Another option is to increase the ISO, making the sensor more sensitive meaning that less light is required to produce an equally bright image.  Doing this would allow for a faster shutter speed (to eliminate the blur) without making the picture darker.

So I took this picture at ISO 400, shutter speed 1/4 and aperture f/5.

Still Blurry.  Still need a faster shutter speed.  Now ISO 800, shutter speed 1/10 and aperture f/5.

Better, but still a little blurry.  Finally, ISO 1600, shutter speed 1/20 and aperture f/5.

This one is less blurry, but now digital noise is starting to degrade the quality of the image.
So what's the lesson here?  There aren't any settings that would have been quite perfect in this situation.  It's just too dark to get a great image - the real answer would be to use a flash or a different lens.  But hopefully you can see when and why you might increase your ISO to get proper exposure.  You can see in these examples both the benefit of being able to increase your ISO and the cost of doing so.