Photoshop User - USA (2019-10)

> PHOTOSHOP USER

>^ OCTOBER 2019

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ANSWERS TO PHOTOSHOP AND GEAR-RELATED QUESTIONS

Sure! But before we get into the nitty-gritty details, let’s

explain in simple terms what we’re actually talking about.

Bit: A “bit” is the smallest unit of measure in computing.

Everything, truly everything, processed or recorded by com-

puter is actually nothing more than a series of zeros and

ones. Each zero or one is a “bit” of information.

Channel: Every digital image with which you work in

Photo shop has at least one color “channel.” Each color

channel stores information about the image pertaining

to that particular color. The vast majority of color images

processed in Photoshop contain three color channels, the

“RGB” channels. All of the colors in an image are expressed

as mixtures of red, green, and blue. You might, however,

work with images in color modes other than RGB. Grayscale

and Bitmap (true “black & white”) images have only one

color channel. CMYK images, usually prepared for com-

mercial printing, have four color channels (cyan, magenta,

yellow, and black). Each color in the image is recorded as

a mixture of those four colors. You might also come across

LAB, Multichannel, Duotone (or Tritone or Quadtone), and

Indexed Color images but these are extremely rare for most

Photoshop users.

Color Depth: The “color depth” of an image is deter-

mined by how much information is used to record the

color of an individual pixel. For 8-bit RGB color, each

pixel is defined by one of 256 specific values in each of the

three color channels. These values range from zero (none

of that color) to 255 (full intensity of that color). Since

each of the three channels can have any of 256 values, the

total number of possible colors in an 8-bit RGB image

is more than 16.7 million. That sounds like a lot, right?

Sure, until you consider an image in 16-bit color. Rather

than 256 possible values for each channel, the image

has 65,536 possible values. Per channel. For each pixel.

With 16 zeros and ones in each of the three color channels,

each pixel can be any of 281,474,976,710,656 individual

colors. Let’s round that down to more than 280 trillion

different colors.

Consider, if you will, a cloudless sky in an image. Blue

skies are rarely uniform in color; they’re typically a gradient

consisting of a number of different shades of blue. Only

some of those 16.7 million possible colors in an 8-bit RGB

image could be considered “blue.” That’s why a close

examination of a sky in some images reveals slight “jumps”

from one shade of blue to the neighboring shade of blue.

An image captured in and processed in 16-bit color won’t

show such abrupt color changes (called posterization).

There are downsides to 16-bit color; for example, the files

are much larger and certain file formats (JPEG in particular)

don’t support 16-bit color.

The bottom line: If your camera captures images in 16-bit

(or higher) color, keep the image in 16-bit color to avoid

posterization and other such problems. If you need a JPEG

copy of an image, stay in 16-bit color throughout the image

processing and save the original in PSD or TIFF format, then

use the Image>Duplicate command and save the copy as a

JPEG. (By the way, there’s rarely any advantage to switching

an image from 8-bit/channel to 16-bit/channel.) n

In the last issue of Photoshop User, you mentioned that you’d explain the advantages/disadvantages

of 8 Bit/Channel vs. 16 Bit/Channel color. Can you do that in this issue?—Nora

PETERBAUER

From the Help Desk