Rod Clabaugh wrote:
Being somewhat new to photography I have a question. When it comes to taking photos how can you tell if a picture is under or overexposed? Isn’t a little subjective? I find the task of photo editing daunting because I’m not sure if I should change a picture or not. It really handcuffs me sometimes because I don’t want to ruin a photo.
First of all... it's up to you how your images look. There is a lot of subjectivity involved. Do what you like. There isn't a strict standard.
Your image appears slightly over-exposed.... But that may be exactly what you wanted, in order to "capture" the "feel and impressions" of a cat basking on a sunny windowsill.
For example, I deliberately over-exposed the following image A LOT to blow out an ugly background, reduce detail on the strongly sunlit flower and draw attention to the tiny subject:
That's what's known as a "high key" treatment of an image. VERY high key, in the above example.
The opposite is a "low key" look.... where the image is weighted toward the dark tonalities:
A silhouette can be an extreme example of a low key image.
A scene may exceed the dynamic range of your camera... so learn to look for situations where lighting is more favorable or control the light with modifiers. That may mean shooting on an overcast day or in the shade or even indoors. Here I used very favorable ambient "North light" from a window (left) and used fill flash (right) to balance overall illumination.
There are many things you can use to control light: reflectors to bounce light where you need it, flags to block it, diffusion panels to soften it, etc.
It also is possible to "compress" the dynamic range through various methods such as multi-exposures or multi-processed images. Here's a shot where my subject was shaded and the background was brightly lit. With a moving subject there was no way to do multiple exposures. It's also not possible to use a graduated neutral density filter (neither a "real" one on the lens or "virtual" filter in software). So instead I double-processed the image: One version was optimized for the indoor subject and color of the light in the shade, while the other version of the image was tweaked to recover some of the blown out background and color balanced for sunlight. Next I combined these two into a single image. I didn't want a "high dynamic range" image. Those can look other-worldly and interesting for some subjects, but here I was striving for a more natural and realistic look (image saturation is slightly boosted due to the method of printing that was going to be used, in this case). Lefthand image is the indoor/subject version, center is the outdoor/background version, and on the right is the result after I combined the "correct" portions from each of those into a single image:
All the above was a "judgment call" by me. I saw the scene, of course, and had some idea how I wanted to render it in a final image. Our eyes can handle a much wider dynamic range than any camera. The above is probably not "true to life", not exactly as we'd see it. I think the finished image is more how our brains interpret all the information our eyes gather.... "Compressing" the dynamic range, in this case to fit what's possible with the camera and the printing process. Notice that the background in the finished image is slightly lightened... once I put the two images together (using layers & masks in Photoshop), I felt that I'd overdone it a little... and made another judgment call to lighten it slightly.
Two additional, important things to consider....
First, is your computer monitor calibrated? Most computer monitors are overly bright for photo post-processing, causing us to make our image too dark. They also usually don't render all that accurate color, causing us to make incorrect adjustments. What looks fine on an uncalibrated monitor might look awful when it's viewed on a different monitor. You need to be able to trust that your computer monitor is showing your images as accurately as possible, both in terms of exposure and in color rendition. There are devices such as Datacolor Spyder, X-Rite ColorMunki and similar used to test a monitor's brightness and color rendition, then help you adjust brightness and create a color profile that's applied to make it as correct as possible. (Note: Ambient light conditions also have to be considered. The lighting around your monitor workspace has to be consistent, too, or it will cause incorrect adjustments.)
It is possible to calibrate "by eye"... but it's a trial and error method that usually ends up wasting a whole lot of printer ink and paper. Invest in a calibration device. Monitor brightness and color change over time, so re-calibration is needed periodically. For example, when I first got my current computer monitor, I found that I had to turn the brightness way down to "20" (not sure if this is a percentage or what).... Now after some years using it, that setting is correct for photo editing at "50". The monitor has changed brightness over the years and gradually needed it's brightness set higher to maintain the same actual level of brightness. If I weren't regularly testing it with my Spyder, I wouldn't know that or be able to set it accurately.
And, another thing, no computer monitor has the same dynamic range as a print. Monitors simply cannot display pure black or pure white. Often if I make a print from an image I discover a lot of shadow AND highlight detail I didn't know was there, because viewing it on screen will never display the full range. This is because a computer monitor is a transmissive display... it's a screen that's lit from behind. A print, on the other hand, is reflective. Light falls onto it and is reflected back to our eyes. The dynamic range is different in a print than it is on-screen. As a result, you might want to adjust images differently depending upon how they'll be used.... If for online display, it may need one rendition. If intended for printing, something different will probably be needed. Much image editing software can have "ICC profiles" loaded to be able to "soft proof" image with an on-screen display that tries to emulate how it will print... but those are never 100% accurate. It can only come with experience, learning to anticipate how things will look in print, versus how they look on screen.
Finally, I really like your cat photo (and tried to stick with that "theme" in my response). I like the slight over-exposure in your image. One thing that bothers me a little about it is that the cat's eye is slightly out of focus. It doesn't spoil the overall feel and effect of the image, but I think would have improved it if the cat's eye had been sharper. A slightly smaller lens aperture or a different point of focus could have changed that. For example, below is a test shot I did with my 135mm f/2 lens when I first got it, to see how shallow depth of field it could render at close distances (with the help of my very patient cat)...
Above image is also a pretty good example of back lighting and some "rim" lighting. (The only light source was a window behind and sligthly to the left of the cat.)