photokaboom

Learn Photography

Photoshop Elements >

Bit Depth: 8 versus 16

Don't Read This?

Photoshop Elements has limited functionality with 16-bit files.

Therefore, you may not need to read much further.

Just make sure—when you're processing a raw file—that 8-Bits/Channel is selected in the bottom of the Adobe Raw Converter.

q

You can select 16-Bits/Channel.

However, there's little you can do with the 16-bit file in Photoshop Elements.

Try it.

Then, go to Image > Mode > 8-Bits/Channel to convert the 16-bit file to 8 bits.

What's a Bit?

When you press the shutter release, photons are collected by photosites on the sensor.

The photons are converted into electrons by the analog-to-digital converter.

The strength of the electrons is measured as voltage.

This voltage becomes a level between 1 and 8—for each red, green, and blue channel in a JPEG file.

The 8 possible voltage levels of each color channel are called bits.

Bits

JPEG files have 8 bits of data for each of the three colors, red, green, and blue.

So JPEG files are called 8-bit files.

Think of bits as being shades of each color.

Each color has 8 shades.

Color Bits (Shades of the Color)
Red 8
Green 8
Blue 8

Each color's 8 shades make other more colors when combined with the other two colors.

Multiply 8 x 8 x 8.

There are 512 combinations—512 colors.

But . . .

. . . bits can be on or off (0 or 1).

Therefore, each color has 256 shades of the color, not just 8.

Color Bits Shades of the Color
Red 8 256
Green 8 256
Blue 8 256

Here's the math.

There are 8 bits.

Each bit has 2 positions, on or off.

So, the two values involved in the calculation are 8 and 2.

Multiply eight twos . . .

2 x 2 x 2 x 2 x 2 x 2 x 2 x 2

. . . to get 256.

Or, 28.

Again, there are:

• 256 shades of red.

• 256 shades of green.

• 256 shades of blue.

How many combinations of these shades are there?

Multiply 256 x 256 x 256.

There are up to 16.7 million colors in a JPEG file.

Now you know why JPEG files are 8-bit files.

What About 16-bit Files?

Raw files may be up to 16-bit files.

There are 16 bits for each color.

Color Bits (Shades of the Color)
Red 16
Green 16
Blue 16

Each of the those bits has two positions, on or off.

A JPEG has 256 shades of each color.

A 16-bit file has 65,536.

Exposure Bits Shades of the Color
Red 16 65,536
Green 16 65,536
Blue 16 65,536

Here's the math.

There are 16 bits.

Each bit has 2 positions, on or off.

So, the two values involved in the calculation are 16 and 2.

Multiply sixteen twos . . .

2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x

2 x 2 x 2 x 2 x 2 x 2 x 2 x 2

. . . to get 65,536.

Or, 216.

Each color has 65,536 shades.

How many combinations of these shades are there?

Multiply 65,536 x 65,536 x 65,536.

There are up to 281 trillion colors in a 16-bit file.

That's a wow, but only for an instant.

The Number of Colors

Isn't Important

We can't see the 16.7 million colors in a JPEG file, let alone the 281 trillion colors in a 16-bit file.

There are two advantages.

Advantage #1

Editing degrades photographs.

With a huge file, we don't have to worry that editing will damage the photograph.

Advantage #2

All digital files have:

• Huge amounts of data in the highlights.

• Little data in the shadows.

A JPEG file is sparse in the shadows.

A 16-bit file is far more robust in the shadows.

Example: JPEG File (8-bit)

Let's say you photographed your best friend's wedding.

You shot JPEGs.

To keep the numbers small, we'll also pretend the couple are leprechauns who wore green clothing.

Now we only have to consider the green channel.

The best shot of the couple is too dark.

The flash didn't go off.

Argh!

Let's say a well-exposed photograph has 100% of the available data: 256 shades of green.

The underexposed photograph of the couple has, say, only 50%: 128 shades of green.

Color Bits % Shades of Green
Well exposed 8 100 256
Underexposed 8 50 128

JPEG File

Here's the histogram.

q

There's not much there.

The data is in the bright-shadows range.

When you edit the underexposed photograph, you're going to spread this limited amount of data:

• Into the shadows.

• Into the highlights.

Below, the Levels sliders were moved in to try to make the photograph look well-exposed.

q

Here's the histogram of the edited photograph.

q

The limited amount of data was spread thinly.

There are gaps on the histogram where there's no data.

The gaps create banding, abdrupt tonal and color transitions.

Instead on a smooth gradation from medium-green to dark-green, there are bands of greens.

Example: Raw File (16-bit)

A week later, you photograph another wedding.

The flash misfires again.

Drat!

But, you shot 16-bit raw files.

The underexposed photograph has less data.

But, there's still a lot of data there because the 16-bit file is so huge.

Color Bits % Shades of Green
Well exposed 16 100 65,536
Underexposed 16 50 32,768

16-bit File

When you edit the underexposed photograph, you'll spread the data into the shadows and highlights.

But, it won't be spread thinly.

There's enough data to fill in the gaps.

You've got 32,768 shades of green.

That's like having a 5-gallon tub of editing paint.

In contrast, the above JPEG file is like having a baby-food jar of editing paint.

More

Go to Raw v. JPEG.

The above information is covered more extensively.

There's also an in-depth discussion of why digital files have less information in the shadows than in the highlights.