The Textbook of Digital Photography - PhotoCourse

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http://www.photocourse.com/itext/pixels/pixels.pdf

http://www.photocourse.com/itext/pixelresolution/

image sensors—image size...

When capturing an image, the number of pixels used to capture it (sometimes

referred to as resolution or pixel count) has a big effect on how large it can be

displayed on the screen or printed. At any given size, more pixels add detail

and sharpen edges. Because numbers matter so much, the best approach is to

shoot using the largest available size. You can always make an image smaller

in a photo-editing program, but you can never make it larger while retaining

the original quality.

The pixel size of a digital image is specified in one of two ways—by its dimen-

sions in pixels or by the total number of pixels it contains. For example, the

same image can be said to have 4368 × 2912 pixels (where “×” is pronounced

“by” as in “4368 by 2912), or to contain 12.7 million pixels (4368 multiplied

by 2912). Since the term “megapixel” is used to indicate 1 million pixels, an

image with 12 million pixels can also be referred to as a 12 megapixel image.

Calculating image sizes

expressed as

dimensions in pixels

(4368 × 2912) or by

the total number of

pixels (12,719,616).

Click for a PDF

Pixels and Curves

read Part 1 on pixels

and image sizes.

Click to explore how

more pixels give

sharper images.

No matter how many pixels an image has, when you enlarge it enough, it

begins to loose sharpness and eventually the pixels begin to show—an effect

called pixelization. This is not unlike traditional silver-based prints where

grain begins to show when prints are enlarged past a certain point. The more

pixels an image has, the larger it can be displayed or printed before pixel-

ization occurs. However, with even inexpensive cameras capturing 6 and 8

megapixel images, most images will never bump up against this limit even

when enlarged to 8 x 10 inches.

Another advantage of larger images is seen when editing. Not only can you

crop them more, changes to such aspects as color balance, hue, saturation,

Square pixels are

arranged in patterns to

form curved lines and

edges in a photo. The

more pixels used, the

smoother these curves

will be. Here the same

red ball is represented

by 4, 12, and then 24

square pixels. As more

pixels are added, edges

become more refined

and the shape becomes

more like the original.

imAge sensors—imAge size