Adobe Photoshop 7 Basics

Adobe Photoshop 7 Color Basics I

Motivation: Demo Levels color correction features of Adobe PhotoShop 7

The next few tutorials will feature color corrections done with some of the pioneering Photoshop color adjustment tools. First we correct for under or over exposure.

The before image The after image

Adobe PhotoShop won an early reputation for superior digital darkroom editing by supporting the broadest range of print and web color models while also having some of the most versatile color correction tools available. Corel, Jasc and Ulead may beg to differ now; but this graphics editor remembers when Photoshop was the most versatile color correction program available.
There are three tools which users can rely on to do much of their color correction work in PhotoShop. The first is the Levels tool which allows for correcting a common error in digital photos - under or overexposure. The other two, Curves and HSL-Hue Saturation Lightness will be covered in the next tutorial. In our sample above we have a case of underexposure exagerating a cooling, bluish tint associated with an overcast day.

The trick in color corrections is to isolate the nature of the color problems on three dimensions. First is the picture underexposed (or too dark) or overexposed /too light? Second, has the image been color shifted - usually becoming too cool(bluish) or too warm(orangish). Third is the image too flat and mottled or greyish in tone;or is the image too contrasty or garish in colors ? The Levels (Image | Adjustments | Levels is the menu sequence) will be used to help make this assesement.

When we use Photoshop's Levels on our window image, its histogram shows that indeed the color spectrum has shifted slightly to the left (in a bad under exposure the histogram would literally climb the left wall). So the first correction we make is to balance the color spectrum helping to correct the underexposure. This involves sliding the white levels (the white triangle at the bottom right of the histogram) to the left - this shifts all the colors to a more even distribution and lightens the overall picture. Next we need to correct the bluish tinge to the photo.

With Levels command there is two ways to do so. First we can use the grey eyedropper (highlighted in the figure above) to select a color patch on the screen whose color should be neutral grey. This in fact is the "brow" of the face. As soon as we click the dropper on the brow the colors shift to a much warmer tone.

Try this with the other two droppers. The left icon is the black dropper. Use this to select a portion of the image that should be pure black. Watch how the color shifts as well as the image lightens or darkens. That is why I prefer to use the intensity sliders first. Because that isolates the correction for intensity alone - not making a color shift too. When using the eye droppers sometimes the colorshift over-corrects and then the color balance is way off.

Likewise, the rightmost dropper sets the white tone. It is useful to have three tone droppers because it is easier to find a patch where one of the three pure tones should appear. But the added power of the Levels tool is that it can make corrections for any of the specific color channels (and it switches color channels depending on which color mode users have chosen. Try switching to the CMYK print color mode - Image | Mode | CMYK. Then choose Levels and note that the color channels have switched from RGB to CYMK).

This means it is possible to also do very precise color shifts. This is the versatility of the Levels tool - users can correct for either the overall exposure using the RGB (or CYMK if you are using that color mode); or users can correct for a specific color only.Our original is slightly bluish so we switched to the B-Blue color channel in the Levels tool and adjusted to lower the blue/increase the yellow. In fact this was the final color correction we made in rendering the image very much closer to the original scene.