|
MEET THE PIXEL
Pixels Are the Building Blocks Of Images
In order to begin with resolution by starting with the pixel.
The pixel is the fundamental building block of digital files. Digital cameras and scanners create pixels. The pixel is
the smallest element of our files. If you can visualize that a digital image is nothing more than a mosaic of pixels
(Picture Elements) that run the length and width of a file, you will soon be on the road to understanding resolution.
As elementary as this may seem,
Figure 1
shows an enlarged view of a file from a digital capture at 1600%. You can easily see the individual pixels that make up the
image as seen in the normal view in
Figure 2.
The file seen here is 1600x2000 pixels. The width is 1600 and the height is 2000-all pixels. This the only information
we need to define the resolution.
One concept to keep in mind is that a digital image like the one shown in
Figure 1 and
2
really has no size but rather a volume that occupies on the hard drive. For example, we know two specifications
about this file. First, we know it contains 1600x2000 pixels.. We can also see that this color file requires
9 MB of space on the hard drive (the file is in a TIFF format. |
 |
Figure 1
(enlarge view)
Figure 2
(enlarge view) |
At this point, the file has no determined physical size. It only fills a certain volume of storage space. Obviously at some
point we need to view or print this image using the pixels running both dimensions of the file. For discussing resolution, we
need to talk about dividing these pixels into a unit of measurement. One common unit of measure in this country is the inch.
Therefore we will use pixels per inch or PPI. Pixels per centimeter, pixels per foot or any other method of measure could be
used. PPI is the method you should use when describing the resolution of a digital file. However it’s common for people to use
DPI. Semantically this is incorrect. Dots Per Inch is a method of describing output resolution because printers and monitors
create dots. Digital cameras and scanners create pixels. What we can tell you is that a pixel becomes a dot when it’s output.
For example, let’s say we have a printer that is capable of laying down 300 DPI and we send that printer a scan that has 300
pixels from end to end. The resulting print will be one inch in size because for every pixel one dot will be created. Therefore
each dot is 1/300th of an inch in size. Take 300 pixels, output a dot 1/300th of an inch and you get an image from the printer
that is one inch in size. At this point, it might seem strange as to why you should work at pixel level. With the pixel density
(the total number of pixels that run both dimensions of your file), it’s easy to figure out how large a file can be printed by
also knowing the output resolution of your printer.
Let us look at one other example to drive this home. Let’s assume an RGB is 4000x5000 pixels. As already mentioned, this RGB file
takes up a certain MB of storage space on a hard drive.. The file has yet to be output so it has no physical size outside of the
computer. This file needs to be output to both a film recorder and a dye sublimation printer.
The film recorder allows us to output this file at 1000 dpi. Each dot is quite small at a resolution of 1/1000 of an inch. Thus
we could say this is a very high-resolution output device; at least compared to the dye sublimation printer which has an output
resolution of 300 dpi. The math for the film recorder is quite simple: divide the output resolution (1000 dpi) by the total
number of pixels in the file (4000x5000). In this example, the output will produce a 4x5 piece of film. If we take the identical
4000x5000 pixel file and output that to the dye sub, the resulting print is 13.3 by16.5 inches. In both cases, the file didn’t
change in any way! We simply divided the total number of pixels in our file in two different manners. A pixel was used to produce
a dot that was 1/1000 of an inch on the film recorder. A pixel was used to produce a dot that was 1/300th of an inch on the printer.
Have the identical pixels within our files changed? No, the dots made from each pixel in the file were different in size.
That 1000x2000-pixel file can allow you to create an output that uses dots that are 1/300 of an inch, 1/1000 of an inch or for
that matter any size. There is no reason you could not search for a printer that creates one dot per inch. That 1000x2000 pixel
file would create a huge print and it would look quite course up close. From a proper viewing distance, it may look good. The
output device will take the pixels in your file and that device will determine how many dots per inch are created which affect
the size of each dot. Thus, the size of the final output from a digital file in length and height will now be established. The
same file may be handled quite differently when sent to a different device.
Let’s take a look at another output device. A monitor is an output device much like a printer but the output resolution is usually
72 dpi. What if we have a file that is 216 pixels along one axis. If our monitor is displaying 72 pixels per inch, that file would
show up in Photoshop at three inches (216/72=3) in the 100% view. That’s because that no matter what your image resolution is
Photoshop maps each pixel to a monitor dot. Therefore, the numbers of the resolution will always be accurate. However, as far as
the monitor real estate goes the image may appear all over the place if it is a high resolution image.
|
Order History
![](javascript:NewWindow("figures_pic.asp?photo=irvor_figure1.jpg&figuretext=A+section+of+the+image+is+shown+in+an+enlarged+view%2E+The+magnification+is+1600%25+and+the+pixels%2C+or+building+blocks%2C+are+quite+visible%2E");)
![](javascript:NewWindow("figures_pic.asp?photo=irvor_figure2.jpg&figuretext=Here%27s+the+same+image+as+shown+in+Figure+1%2E+This+time+it%27s+viewed+at+100%25+and+the+pixels+aren%27t+as+noticeable%2E");)
Top