The Professional Photoshop Book - Volume 7 2015

Pro tricks for mastering colour

The Professional Photoshop Book 25

ALL CHANNELS

PREVIEW

HISTOGRAM CHANGES

LEVELS VERSUS CURVES

IMAGE DATA

This expansion to the histogram panel lets you

view the standard RGB histogram so you get an

overview of the distribution of dark, mid and light

tones in your image, but extends that to the Red,

Green and Blue colour channels in your image so

that you can view each one individually. This is an

excellent way to get a full-channel drill-down of

your image for channel mixing or colour grading.

With the All Channels histogram open, you can

click on the individual Red, Green and Blue

channels to view additional information on each

of the colour channels.

When you make an adjustment to colour in

Photoshop, using Levels or Curves for example,

you can preview what those changes will look like

on the histogram. With the histogram panel open,

go to your adjustment of choice and make sure

that Preview is ticked. Now when you make

changes, you’ll see how they’ll affect the

histogram, giving you complete control. It’s worth

noting that this works via Image>Adjustments

only, not on adjustment layers.

The basic difference between Levels and Curves is that Levels allows you to correct the overall tonal

balance of an image, broken down into shadows, midtones and highlights, while Curves allows you to

adjust individual points in an image’s tonal range. Many Photoshop users favour one or the other for

adjusting images, but the truth is that they both have a place in your image-editing workflow. Both of

them offer you the option to save presets so that you can apply the same adjustments to multiple

images or image assets, and both allow you to drill down into colour channels to make individual

adjustments. Where they differ is that generally, Levels is used to make tonal adjustments to the

image as a whole, and while Curves can do this, it also allows you to make adjustments to individual

tones and colours within the image without altering other parts of it.

On the left of the histogram there’s some

mathematical data. ‘Mean’ represents the overall

intensity value. ‘Std Dev’ stands for Standard

Deviation and shows you how widely the intensity

values vary – a high number means a lot, a low

number means a little. ‘Median’ represents the

middle value. ‘Pixels’ shows you how many pixels

were used to calculate the data. Then on the right

• Brighten or darken an entire image


• Adjust colours across an image


• Boost contrast across an image


• Brighten or darken individual
  colour channels


• Adjust tonal range across an entire image
  
  
  • Adjust individual points within tonal range
  
  
  • Adjust colours and tones
  
  
  • Add contrast to midtones
  
  
  • Change the values of black and white
  
  
  • Adjust highlights, midtones and shadows
    individually across colour channels
  
  
  
  

WHAT’S THE DIFFERENCE BETWEEN THESE TWO COLOUR TOOLS

AND HOW CAN YOU MAKE THE BEST USE OF THEM?

ADVANTAGES

OF LEVELS

ADVANTAGES

OF CURVES

hand side, ‘Levels’ shows the intensity level of the

area under the cursor when you mouse over the

histogram, ‘Count’ shows the total number of pixels

that correspond to that intensity value, ‘Cumulative’

shows the number of pixels at or below that level,

and ‘Cache’ shows the image cache level, which

governs how quickly Photoshop samples and reads

the data – the higher the better!

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