Get a grip on the basics (more post-processing made easy)

Started Feb 20, 2004 | Discussions thread
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Gordon W
Gordon W Veteran Member • Posts: 3,839
Get a grip on the basics (more post-processing made easy)

Lots of folks have explained histograms here and on other web sites, but there still seem to be a lot of people who don't understand them, so I'm going to give it a try here of my own because being in control of how an image’s tones are distributed is the key to making post-processing easy. And it really is easy once you get a grip on the basics of what’s really in a digital image. Really!

And to control the tones of an image, the two most single powerful functions in Photoshop (or any image editor) are Levels and Curves (or whatever your editor calls them). If I could only keep two of the myriad commands in Photoshop, those two would be Levels and Curves. Hands down. No contest.

Why do I say this, you ask? Because an image is nothing more than shades of color (actually shades of gray, but I won't hit you with that yet) that ideally range between the two extreme points in any image, black and white, and with Levels and Curves you can basically control how these shades are distributed between those two extremes. For now we’ll work only with Levels since it shows the image’s histogram, a graph showing how the tones of an image are distributed.

To illustrate, below is a photo of my granddaughter Grace sent to me by her mother (my daughter) who uses a Fuji digicam. Notice how the image looks dark (no snide comments please, this can happen with any digicam ;-). Also notice how the tones of the image represented by the ‘mountains’ in the histogram beside it are all bunched to the left side toward that black triangle (the Black Point).

This histogram tells me that the brightest tone in this image is just a little brighter than middle gray (represented by that gray triangle, the Midtone Point). If this graph represented distribution of people on a boat, it would be capsizing.

Obviously, from looking at the subject of the image, it should have tones much brighter than midtones. In fact, in most cases your mind expects to see an image with tones that range from black thru midtones to white, even if the original subject didn’t have tones that were truly at those extremes.

So to brighten up those dingy tones, we tell the image editor that we want the rightside end of the ‘mountains’ to be white. To do this, we simply click and hold on the white triangle (the White Point) and drag it over to where the ‘mountains’ end, like this...

If you have the Preview option selected, you will see the image brighten up right before your eyes. Hit Enter or Return and you’ve just accomplished one of the most basic yet important post-processing operations in digital photography. Levels is invariably the first thing I check and correct with nearly all my digital images. If this isn’t right, nothing else can be.

If you look at the histogram again (by calling up Levels) it should now look like this...

Notice how the tones of the image now range between black and white and the image looks a WHOLE lot better.

However, it still has some problems when viewed on my calibrated monitor. It still looks a bit dark overall and the color balance is a bit reddish (the wall should be neutral not pink).

No problem. As seen below, you can brighten the midtones by simply clicking and dragging the Midtone Point to the left, which tells the editor you want those darker tones to be brightened to midtones. Color balance was adjusted by editing the levels of each R, G, and B channel individually, but that’s a topic for another time.

So, here you have the same black and white points as set originally, but the tones between them have been redistributed to give better color and shadow detail. In essence what we did was extend the dynamic range of the original image and then improve it.

If this hasn’t totally confused you and there’s enough interest in this topic, I’ll continue.

 Gordon W's gear list:Gordon W's gear list
Canon PowerShot S100 Panasonic FZ1000 Nikon Coolpix B700 Canon EOS 500D Canon EOS 60D +3 more
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