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

Started Feb 20, 2004 | Discussions thread
Maria Sanderson Junior Member • Posts: 35
Thank you...Grazie...Meci

I love simple explanations! That's a keeper!

Thanks again.
maria

Gordon W wrote:

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.

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