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Digital Data Terms

This section has two parts.

Pixels, Bits, & Bit Depth

Pixels

The term pixel is from picture element.

When photons are collected by the millions of photosites on your camera's sensor, pixels are created.

These pixels are the small squares that make up your photographs.

Most people can skip the next section about bits and bit depth.

Bits & Bit Depth

Each pixel is made up of data called bits.

A pixel in a JPEG file has 8 bits of data for each of the three colors, red, green, and blue.

Color	Bits
Red	8 bits
Green	8 bits
Blue	8 bits

Each of those bits has two possibilities—it can be either on or off.

With 8 bits, and with each bit being either on or off, there are 256 combinations for each color.

Here's the math.

Take the number of bits, 8, to the power of the number of possibilities for each bit, 2, to get 256 possible combinations (8²).

Color	Bits	Each Bit	Total Possible Combinations
Red	8 bits	Can Be On or Off	256
Green	8 bits	Can Be On or Off	256
Blue	8 bits	Can Be On or Off	256

Now, if we combine the three colors, there are 16,777,216 possible colors for each pixel.

Here's the math.

256 x 256 x 256 = 16,777,216

Take the number of possible combinations for each color channel, 256, and multiply them together.

So, there are 16.7 million possible colors in a JPEG with a bit depth of 8 per color, or a bit depth of 24 for the entire file.

Advantage of 12-Bit Raw Files

Raw files generally have a bit depth of 12 per color channel, for a total bit depth of 36 for a file.

Each color channel has 4,096 possible combinations—compared to the 256 of a JPEG color channel.

Take the number of possible combinations for each color channel, 4,096, and multiply them together.

4,096 x 4,096 x 4,096 = 68,719,476,736

There are 68 billion possible colors in a raw file with a bit depth of 12 per color channel, or a bit depth of 36 for the entire file.

With all of that data, you can do extensive editing without the loss of quality that would occur when editing a JPEG file.

Whenever you edit, some of the data is degraded.

With more data, a raw file will have a far smaller percentage of degradation that a JPEG file.

For more about Raw files, go to Raw v. JPEG.

Bytes, Kilobytes, & Megabytes

Definitions

Bytes, kilobytes, and megabytes are measurements of the size of photography files.

A byte is the smallest unit of measurement.

There are a thousand bytes in one kilobyte.

In turn, there are a thousand kilobytes in one megabyte.

That's 1,000 x 1,000 = 1,000,000.

Because a kilobyte has a thousand bytes, multiplying it by a thousand equals 1,000,000 bytes.

One Kilobyte	One Megabyte
1,000 bytes	1,000,000 Bytes

You may encounter slightly different amounts.

Sometimes, the following figures are used instead of a 1,000 and 1,000,000.

One Kilobyte	One Megabyte
1,024 bytes	Bytes Bytes

These numbers are actually more accurate.

Processing Speed of Different Sized Files

The size of a file affects how fast various operations can be performed.

Saving

Large files require more time to be saved to your memory card after you press the shutter release.

This can be an issue if you're taking many photographs in quick succession.

Many cameras have a burst mode to facilitate this activity.

Editing

Large files also take longer to process when editing.

However, because you have more to work with, the final photograph may be of higher quality.

Uploading & Downloading

The speed of uploading and downloading files, the sending and receiving of files, depends in part on the size of the files.

If you're e-mailing files, your e-mail program will reduce the size of large files.

Megapixels & Pixel Dimensions

Megapixels

Megapixel is the measure of the devices that collect the photons, to make pixels, on the camera sensor.

One megapixel is one million of these devices.

So, one megapixel will produce one million pixels.

A twelve megapixel camera will produce twelve million pixels, for example.

Pixel Dimensions

The twelve million pixels are arranged in a rectangular array called the pixel dimensions.

Size of the Photosites

Is a twelve megapixel point-and-shoot camera making a photograph that has the same quality as a twelve megapixel digital SLR?

No.

The two cameras have the same number of megapixels, but more data is collected by the digital SLR.

That's because the photosites on the sensor of a digital SLR are larger.

They gather more photons, making for pixels with less noise in relation to image data.

Go to Are More Megapixels Better?.