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Photoshop Tutorial: More luminosity

By: ledirlo

I'll say it again: luminosity is the key to making good pictures; for those who don't know , PHOTOgraphy means "light-print".Photo means light (photon), when your eyes see an object , it doesn't see the object but the light it reflects, absorbs, and/or emits.The intensity of light , it's tint, falloff , difuse map are what make your brain recognize an object.Therefore, everything you do when you retouch a photo is to alter the caracteristics of its light; a good , simple example is when you enhance a landscape : you'll use curves, hue, etc, that all are commands that alter the luminosity.Since 99% of you work on RGB monitors, photo retouching consists in altering the value of each red, green and blue pixel in a picture, modyfying the light it emits.

I just wrote this part because most people don't think of that and therefore dont understand the way photoshop works, and wonder why I emphasize so much on luminosity.Now I'll share some luminosity correction tips so you can practice :

1: bad exposition

You just shot a pic , and the fact is that the exposition is bad: some parts are visible, some are too dark.uneven luminosity.Here's a pic of my nephew Lucas:


O
bviously the background on the left is too dark, so let's try this :

D uplicate the layer, (ctrl+j), invert the luminosity of the duplicate (ctrl+i), put it in soft light mode, and give it a 9.0 gaussian blur:hooray the dark part is now visible !



The problem is that it also altered the luminosity of the kid, therefore just duplicate the soft light layer for safety, turn it off, and erase the part of the visible one that overlaps Lucas with a large soft brush to get rid of the luminosity settings the layer contains , and so you restore his original luminosity


Y
ou can see the shape of the layer in the layer palette: that's a way to correct bad exposition , and even a pic's luminosity in a non destructive way.

2: Low contrast

If you shoot a pic and it has a low contrast, it means that his alpha channel, or luminosity values are too modrate, low, even; in other words, the black point and light point are not visible enough: I lowered the contrast on the pic of Lucas to make an example


Y
ou have two very good ways to fix it:

A: create a luminosity map:

Duplicate the layer, desaturate it (ctrl+shift+U), put it in luminosity mode, and press ctrl+L


Y
ou can fix the saturation by adding a little, and it's done!


Just compare with pic 4 to see if you like it.

B:Jerry's trick:

Jerry717 taught me and a few others that were on the discussion board this trick; it's a very good example as it is efficient, easy, and practicing it will make you understand the whole luminosity thing.

Take pic#4, create a curves adjustment layer over it; double click the eyedropper on the right


An
d fill in the rgb values with "250" : this prevents the picture to contain a white point that would contain extreme, non printable color values.Press enter, and , again with the same eyedropper, click on the bright part of Lucas' t-shirt.

Now double click on the left eyedropper (set black point), and enter "3" as rgb values for r, g, and b.press enter and click in the darkest zone in the left side upper part of the pic .

Now do the same with the center eyedropper (set gray point), enter "128" as rgb values: this makes your pic have the right, neutral color values.then click the eyedropper where the arrow points at in pic 8


Th
is sets the gray point of the picture , and makes it get rid of the opposite color that it contains.Try it everywhere on the pic to understand what I mean.

Now just press enter to get out of the curves layer, duplicate the layer and do this :put the adjustment layer in luminosity mode, duplicate it, and put the copy in color mode.This lets you tweak each different settings aprt from the others.Otherwise if you like the original result, just put your adjustment layer in normal mode...the result I have is this one



The great thing about jerry's trick is that it also prepares the pic for printing, since it implies good black point and light point values, both for the eye and the printer.Thank you Jerry !!!!

Photoshop CS added a "shadow/highlight" command that basically does the same, but it doesn't explain you how it works....I prefer the old way.

You could have tried the second trick "luminosity layer" with an overlay layer instead.....just try some more, using opposite values, deasturated layers so you understand precisely how this works.

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