White-Balance Chart in Canon

[Carroll]

I am not a pro photographer, but did have a 35 mm some time back. So I'm familiar with basic concepts like adjusting aperture or shutter speed, and I understand ISO better now that I’m using a digital camera.

I have a Canon Power Shot SX110. I see how I can change the WB settings with presets under AWB. When I take a series of pictures using different settings and then play them back using the Dist. Button to bring up the tech. information, I see Canon’s white-balance chart. I see that each image has a different chart, but I don’t know what I’m looking for in the chart.

When I compare only pictures that have good balance, I still don’t see a pattern to the charts. What can that chart tell me? Do I want a nice bell shape in the center? Do I want an equal amount of white to black throughout the graph? Or is there no template that works for all pictures?

Carroll

[Colin Southern]

Hi Carroll,

I'm not familiar with that particular model, but my guess is that what your seeing is the histogram, and not anything to do with white balance.

A histogram is simply a graph of how many pixels are recorded at each brightness level, which aids in judging how good the exposure was. An under-exposed shot will have the graph bunched up towards the left hand side of the graph whereas an over-exposed shot will have them bunched up towards the right, usually with a sharp spike right at the end.

As a rule of thumb (but there are exceptions) the ideal exposure is one that takes the histogram right up to the right hand side of the graph, but not beyond (as this uses the full range of sensor values - even if the image looks over-exposed on the built in screen) (you adjust the over-exposed look in post-processing later).

Hope this helps.

Cheers,

Colin - pbase.com/cjsouthern

[Carroll]

Thanks. Histogram is indeed what I was seeing. Armed with the right terminology, I found the Cambridge in Color tutorial on histograms.
The Canon guide book even has 'histogram' in the Index -- a terse paragraph with a simple "keep it in the center" message. It does point to an function on the camera called 'adjusting exposure compensation' which is a bar showing how much exposure you're getting by adjusting aperture and shutter speed as you prepare to shoot.
I have been doing that adjustment already to avoid wildly over/under exposures. Still the various histograms of my keepers are quite different from each other. In some I see a match between the outcome and bunching at one end or the other of the histogram. With others I don't see any correlation. The tutorials help with that issue since the averaging of the three colors' values is what the histogram shows.
So Canon's histogram tells me less than just looking at the picture. I doubt if I should spend more time on histograms than some other issues as I learn to take pictures.
Again, thanks,
Carroll

[Colin Southern]

Hi Carrol,

You're welcome.

Surprisingly, correct exposure in a digital envoronment can be quite complex - depending on the scene.

Sensors have a near linear response curve - which means when the charge on the sensor photosites are converted to digital (say for example a 12 bit A/D converter), 2048 of the possible 4096 levels are devoted to the brightest stop; of the remaining 2048 levels, 1024 of these are devother to the next brightest stop (and so on and so forth).

Therefore ...

If you under-expose a shot by a full two stops then you're throwing away a full 3/4 of available values that represent tone levels. In this scenario when you scale the remaining 1024 levels across the full range of tones you risk banding in the highlights - posterization of the shadows - and noise levels will be increased. A histogram lets you see in an instant how much a shot is under-exposed - and tells you how much EC you need to apply to get it spot on - so in that respect it's a valuable tool.

Over-exposure on the other hand is a different story - and in this respect the camera's highlight warning feature ("blinkies") give a better warning as to areas of blown highlights.

There are exceptions to the rule, but as a rule, an exposure that "looks about right on the screen" is almost never optimal - and only a histogram tells you the story of how much - so in that respects it's a very valuable tool.

What makes the whole thing complicated is that the correct exposure depends on the scene - a forrest scene with flat lighting needs to be handled completely differently to - say - one that includes a vehicle with specular highlights reflecting off a chrome bumper - which varies again to the required techniques for correctly captuing a sunrise or sunset.

In practice I use the histogram a lot - but in conjunction with the highlight alert feature AND a lightmeter for both incident AND reflected readings.

Hope this helps,

Cheers,

Colin - pbase.com/cjsouthern

[David]

Hi Carroll - I'm going to back Colin's advice re histograms. They are one of the most important innovations associated with digital photography. The more you get into digital the more you will use them and rely on them to improve exposure and post-processing. I have to say that very often when I shoot with my Canon, I look at the histogram first before checking the scene! However, I do appreciate that it may take time to twig the usefulness of histograms. People like me, who have been using graphs and "grams" in their work, can see the benefits right away, but if you've been using film only then histograms can seem of little benefit.

Your initial post concerned the white balance settings and you commented that you could see differences in what we now know as the histograms, but you did not know what you should have been looking for. The ability to manipulate white balance is another of the great innovations associated with digital. White balance is to do with how colours look under different coloured light (e.g. natural daylight versus tungsten lamp). As far as exposure and histograms are concerned, if you shoot a scene under say tungsten white balance and then under say cloudy white balance, the detailed shape of histogram will change, but the general outline will be much the same. There is not that much you can read into those small changes and I doubt that you should worry about these detailed changes at this point. I suggest that you stick to AWB for the time being.

I hope these points help and Happy Shooting.

Cheers

David

[Carroll]

Hi, David,
A further tour of the tutorials has left me with little doubt that the Histograms do hold the key to the big picture. I will have to understand things like color, however, before I'll get what the Histogram is saying about it. The Green Red Blue scheme and all of its ramifications, for example, are new to me. I always knew there is more than one way to play with color. But what happened to the 'blue and yellow make green' scheme I grew up with? Neither Additive nor Subtractive fits the rainbow I thought I understood. Do people look at a melon and see how much low, mid and high red is in it? the blues? along with hue and saturation?That's what I want to do.

Looking in the tutorials I was inspired to look in Corel Paint where there are tools for manipulating the color channels, et.al. Since I can view what Canon says about a picture side-by-side with what Corel Paint says about the same picture, and how it looks on a Histogram after it's been edited, it should be fun leaning some of the technical stuff about taking pictures.
Carroll

[Colin Southern]

"I will have to understand things like color, however, before I'll get what the Histogram is saying about it."

If you're a glutten for punishment, the industry standard reference for understanding colour from camera to print and everything in between is Real World Color Management by Fraser, Murphy, and Bunting. It's heavy going in places, but frankly, there's no substitute - nothing else even comes close. Available through amazon.com if this helps.

Cheers,

Colin - pbase.com/cjsouthern

[Carroll]

I'll keep the reference of Fraser on hand, and my ears tuned in for it in my quest. My actual gluttony is cyclic, so I tend toward shortcuts -- mastering just enough for now to let me work the camera and have some fun.

I'm also realizing that I need to start paying attention to the what I see in the world. Looking at the TV is a challenge to analyze the different photographic aspects of the changing picture. It's a right-brain thing to see the world, but left brain to translate that into camera think.

I was definitely in the wilderness clicking between my camera and my little user guide that came with it, not knowing white balance from histograms. Then I found this web site and the big picture came into view. The tutorials are not only good, but also stake out the boundaries of where to start. Suddenly I realized how the camera's settings relate to computer software tools, and how the software lets me experiment with the principles, something I can't do with the camera

I really appreciate everyone's help.
Carroll

[Colin Southern]

"The tutorials are not only good, but also stake out the boundaries of where to start."

I agree whole-heartedly. I think our esteemed leader Sean has a great combination of technical excellence combined with the ability to explain complex topics in a relatively clear and straight-forward manner - it reminds me of the style of the late Bruce Fraser.

Sean - if you're listening ...

... it might be time to start thinking about expanding on your tutorials and putting them altogether in a book! ("The Sean T. McHugh Master Guide to Digital Photography" - "Tips, Traps, Technologies, and Techniques for Photographers at All Levels").

Cheers,

Colin - pbase.com/cjsouthern

[d3debian]

Oke, is Sean the one responsible for the tutorials.
They are fantastic and i was in doubt to ask the creator to write a book.
I did not because i was afraid his answer will be " read the tutorials online or print them on paper yourself".

Now Colin write about the tutorials in a book i want to support his idea.

I 've read much websites and fora about photography and none of them are that helpfull and explain that clear as cambridgeincolour.

So if, in future time, a cambridgeincolour book get produced, put my name on the orderlist, somewhere on top.