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RESOLUTION AND FILE SIZE
There's A Cause And Effect Even Though They're Not Related
At this point of the discussion, let’s look at both resolution and file size however, in this case size refers to the file stored
on the hard drive and not output. The resolution of a file and the space it takes up on a drive aren’t related in this discussion
because the pixels in our theoretical file are identical (let’s say 1000x1000). Nevertheless, this 1000x1000-pixel file could have one,
three or four channels and therefore the size of the file will change, as the resolution will not. For example, a 1000x1000-pixel
grayscale file will be a third the physical size as a 1000x1000-pixel RGB file! That’s because the RGB file has three color channels;
one for each red, green and blue channel. A CMYK file will be one channel or a fourth larger than the RGB file. Knowing the pixel
dimension, allows one to calculate the actual physical storage size a file will be no matter the color mode and here is how:
Take the pixel dimensions and multiple them to get the file size. If we have a file that’s 1000x1000 pixels, we would multiply
1000x1000, which equal 1,000,000. This is the total number of pixels in our file. Multiply those figures by the number of color
channels. For an RGB file, that would be three. So therefore you would multiply 1,000,000 X3 or 3,000,000. Divide that by the unit
measure of bytes which is 1024. So that would be 3,000,000/1024= 2929. Divide once more by 1024 to get the number of megabytes. The
result is 2.86 MB.
Knowing the pixel dimensions provides just enough information to always figure out how much storage space a file should take without
taking into account any compression applied.
Caveat! Not all pixels are created equally! We’ve covered at some length how it’s important to deal with resolution at the pixel
level. Hopefully it makes a some sense. If not read this section again. Be aware that there are issues far more involved in the
quality of resulting images then simply matching the pixels to an intended output device. While it may seem obvious, the final
output quality will highly depend on the quality of the pixels in a file. Not all cameras or scanners that can create 1000x1200
pixel files equal in quality. There can be a vast differences between any device that creates pixels even if one device is capable
or producing far more pixels per inch than another. This is especially true for digital cameras. Too many digital camera buyers look
at the resolution a camera is capable of providing as the Holy Grail of quality. There are plenty of factors affecting the quality
of a file. The CCD and it’s noise level, the Analog to Digital converter, the optics of a lens, as well as the amount of compression
all work together to play a role in how well an image is captured and output.
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