> PHOTOSHOP USER>^ MARCH 2020[ 120 ]
ANSWERS TO PHOTOSHOP AND GEAR-RELATED QUESTIONS
First, not all image pixels are square; some are rectangu-
lar. (Rectangular pixels are used for some video formats,
including D1/DV, HDV 1080/DVCPRO HD, and Anamor-
phic 2:1 projects.) But square or rectangular, image pixels
are arranged in a raster, a grid in which each pixel perfectly
aligns with those above, below, and to the left and right.
You can see this in Photoshop when you zoom way in on
an image.
Because each pixel used to represent a curve or diagonal
line has sharp corners rather than rounded or angled edges,
the screen shows a stair-step pattern where you would
hope to see a curve or line with well-defined, smooth
edges. You might also see a series of lighter colored pixels
along a curve in an image. That anti-aliasing helps fool the
eye into seeing a smooth curve when not zoomed in.
When the image displays a distinct stair-step pattern
along curves, you can use the industry-standard term
“jaggies.” (For example, “That low-res image has a bad
case of the jaggies.”) In addition to jaggies, low-resolution
images will have substantially less fine detail. In a photo
that measures 5760x3840 pixels (if the camera was prop-
erly focused when the image was captured), there’s likely
lots of detail (unless, of course, the subject of the image
was itself very smooth). If that image is downsized to 10%
of its size (576x384 pixels), perhaps for use in a presenta-
tion or for a thumbnail on a webpage, there’ll be much less
fine detail and a greater chance of jaggies.If you need a small image for a thumbnail or other pur-
pose, there’s not much you can do about the lack of detail.
In such cases, though, it’s unlikely that the viewer will
zoom in or enlarge the image, so the lack of detail won’t
be particularly bothersome.
When printing an image, the number of pixels is
extremely important, as are the corners of those pixels. Say,
for example, that you’re printing an image at 8x10". If the
image measures 800x1000 pixels, the image’s print resolu-
tion is 100 pixels per inch (abbreviated ppi). In other words,
each of the image pixels will be reproduced by the printing
device at a size of 1/100" square. That may not seem very
large but, in terms of a printed image, it certainly can be
(depending on the quality of your printer). For instance, in a
portrait, the eyelashes may lack definition or in a landscape,
the branches of distant trees may not be distinguishable.
If the same 8x10" image measures 2400x3000 pixels,
the print resolution is 300 ppi and each image pixel is
reproduced as a square measuring 1/300" per side. Those
substantially smaller printed pixels can reproduce much
more fine detail.
So, once more back to the “squareness” of pixels. The
larger the image pixel (1/100" square vs. 1/300" square), the
more likely you are to see those pesky corners poking out
along curved or diagonal lines. When anti-aliasing is used to
help hide those corners, the edge or line becomes less distinct,
“softer” to the eye, and fine detail is lost in the image. nWhy is it important to understand that image pixels are square?—RasmusPETERBAUER
From the Help Desk