Monday, February 18, 2019

Histograms and your shot (part 2)

Photos of a male American goldfinch; overexposed, properly exposed, and underexposed.
This shot of an American goldfinch was taken last year when I went on a camping trip with my students that were involved in my photo club.  All three images come from the same RAW file; I processed each one so that the relative exposures were different.  Each image has its associated histogram with it.  The far left image is underexposed by a stop, so half as much light as is required.  The center image represents a proper exposure and the far right an overexposure, again by one stop (double the light).

As was mentioned earlier, the key to working with histograms is to pay attention to trends and not to get bogged down with the details.  Notice the dark values for all three histograms (A, C, and F).  There are a lot of darker values for the underexposed shot than for the overexposed one.  The properly exposed image has some dark values, but they do not represent the majority of the scene.  If the image was naturally dark with some bright areas it would be different, as you would expect to see a greater number of darker values.

The light values for all three histograms (B, E, and G) show a similar, although reversed, trend.  There are very few light values in the underexposed shot, and way too many in the overexposed one.  The properly exposed image has some brighter values, but really not too many.  If this was an image with a lot of whites in it, such as a snow scene, I would expect there to be many bright values.  However, in an average scene, there should not be such a pile up in that corner of the histogram.

The central histogram is properly exposed.  Notice that there are few dark and light values and that the central portion of the histogram contains the bulk of the pixels.  If you see bars of a histogram being shoved to one side or the other, especially with there being a flat, empty area on the other side, your image is very likely improperly exposed.  How do you go about correcting this?  That we will leave for another time.

Sunday, February 17, 2019

Histograms and your shot.

Gouldian Finch at the Vancouver Conservatory
I have taken my photography club from school to the Vancouver Conservatory every year.  It is inexpensive and fun, not to mention an education in photographing members of the feathered fellowship.  They have quite a few species of exotic birds there (see link below).  They are well looked after and modestly used to a human presence.  It makes the business of photographing them a little easier.  After all, it is easier to take pics of something not desperately trying to get away from you.  I have seen many people use their cell phones to capture some pretty good images.

The strange little graph in the right upper corner is a histogram.  Chances are you have seen them before, probably in association with pictures on your camera.  Histograms are an empirical way to examine light information on an image.  The histogram here is a gray scale image combining all the coloured information together of the bird photo.  It would be exactly the same if we converted the coloured image to a black and white (gray scale) one.  The left side of the histogram shows the darker shades while the right side shows the whiter shades.  The values progress from completely black on the far left to completely white on the far right.

A histogram is made of 256 little bars.  Each bar represents a shade of gray.  It starts from 0 at the right for white and 255 at the left for black.  Each bar in between those two extremes would be a number; the darker the shade of a pixel the higher its associated number.  The height of each bar tells you how many pixels in the image are made of that particular shade of gray.  You can't really see the bars, and you don't need to.  The trick with histograms is not to get worked up by the insane amount of data, but rather to see the trends within the data. 

There are primarily three trends which you should know.  The overexposed trend, the underexposed trend, and the properly exposed trend.  Each of these is unique in its own right, kind of how a fingerprint is unique for each finger for the whole human population.  Still though there is a certain way that those bars form.  Once you know what you are looking for, the rest is relatively easy.  The great thing about interpreting histograms is that they can help you improve your shots.  A lot.

My next blog will be on the three trends.  It will also be on this same birding blog.

Birds at the conservatory:

Friday, February 15, 2019

Turkey vulture

The turkey vulture
The iconic vulture is a bird which feeds primarily on carrion - the flesh of dead animals.  That may seem a little nebulous, as most predators will kill something first then eat that which has just expired.  Turkey vultures then are opportunistic carnivores that actually don't kill to eat.  Rather, they enjoy the bounty of something that has died on its own or been killed by something else.   The distinction is important because of the reputation they have been branded with over the centuries.  Quite frankly, it is unfair.

The roll vultures play in nature is actually very important.  They go about their business and clean up the mess left behind.  They are nature's way of not letting good food go to waste.  What they don't get will be taken by others, such as all dogs and their relatives on land (coyotes, jackals, and so on), by fish and their relatives in water, many invertebrates, and ultimately by bacteria, protists, and fungi in all environments.  We call this group the scavengers and decomposers.  If it was not for these important niches of organisms the world would be filled with the remains of dead things. 

Consider the image of a skeleton of some long gone creature and a vulture sitting on a branch nearby.  Another popular meme is the cowboy dying of thirst, crawling on the desert, and vultures soaring overhead.  It does impart a certain dose of the heebeegeebees in one's mind, I suppose primarily because they would not be kind enough to wait until death had fully set in.  Being opportunistic, they would much rather be at the party first.  No sense showing up after all the good parts are gone.

We associate vultures with death, and all associated icons receive similar disdain.  Whether it be Scrooge and the Ghost of Christmas Future, the Spectre of Death, or even the ever eerie headstone with your name on it, they all speak of a foreboding finality.  I think that our view of death is not a global phenomenon, but very much a western understanding; death is something to be terrified of.  I recall a scene in "The Lord of the Rings" where Gandalf and Pippin are awaiting their demise.  The wizard helps Pip's fear regarding what they imagine is inevitable.  Scary and uncertain, but also bringing about a welcome peace filled with wonder, the concept of death is given a very different view.

If people saw death in this way, the vulture may be viewed in a totally different light.  They may be looked at the same way we see doves.  Not harbingers of death, but bringers of new life and peace.  I guess it is all in the way you look at things.