Michael,
Please do not use the term resolution when describing pixel
dimensions. Call it actual pixels. Everyone assumes that resolution
is the density of pixels (PPI) within an image and they already have
to understand what it is you're describing to understand that what
you mean by resolution isn't what they are used to seeing.
Larry
>Some of you are still getting confused between PPI and the actual
>pixel resolution in a given image.
>1. Pixel resolution is how many pixels are in your total image from
>side to side, top to bottom. If you don't know your camera's
>resolution, look in your camera manual, or check out the data in
>your RAW or Jpeg file. Mine is 4080x4080 pixels. Meaning my file has
>4080 pixels from side to side, and also 4080 pixels from top to
>bottom. It is a square sensor. Your sensors, unlike mine, are
>rectangle, so your resolution may look something like 3000x4500
>pixels. Meaning that your file is (in landscape mode) 4500 pixels
>from side to side, and 3000 pixels top to bottom. If you multipy the
>two (4500x3000) it will indicate the exact mega pixels your sensor
>can create (mega meaning one million). So if this is your
>resolution, you have a 13.5 mega pixel camera. Mine (4080x4080) is
>16+ mega pixels.
>
>2. PPI (pixels per inch) simply indicates how many of these pixels
>YOU assign per inch in your image file. Most cameras default to 72
>pixels per inch (ppi) when uploaded to your computer. You can change
>this default in your RAW processor to whatever you want. The more
>pixels you assign per inch, the smaller (in inches) your image will be.
>
>Here's how to figure out ppi and inches in your desired print size -
>Take your camera's resolution, and divide it by a pixel number to
>determine it's size in inches, OR...divide your resolution by inches
>to determine what your ppi will be.
>Examples - If I assign 72 pixels per inch (4080 divided by 72), my
>image will be 56.67 inches long. If I assign 360 pixels per inch
>(4080 divided by 360), my image will be 11.33 inches wide.
>Or, say, if I specifically want a 24" print, I would divide my
>resolution by 24 (4080 divided by24), which would yield 170 ppi for
>my print. Of course, PS, LR, etc will do all this for you, but the
>purpose here is to understand WHAT is going on. Note - In NONE of
>these examples have I altered my file in any way - I have not added
>nor deleted a single pixel. In each case I worked solely with the
>original 4080 pixels. My original resolution remains intact.
>You run into problems when you start arbitrarily adding or deleting
>pixels. Avoid this whenever you can. Remember, if your original
>resolution remains between 180-480 ppi (and I've gone as low as 150
>PPI) for your desired print size or web size, DO NOT alter the
>resolution. Send it to the printer as is. In other words, DO NOT
>interpolate or resample if your ppi remains between 180-480 for your
>chosen print/web size. In today's world, with larger sensors, you
>will most likely have to resample when web posting, as most files
>are simply too large to begin with.
>
>3. Now here's the final kicker - your Epson printer defaults to a
>360 ppi file for printing. Other brands default to 300 ppi for
>printing. This means that NO MATTER what your file's ppi is set to
>when you send it to your Epson or other brand printer, your printer
>will add or delete pixels to come up with either 360 or 300 ppi
>depending on your brand of printer. So if your file's ppi is bewteen
>180-480, again send it as is, and let the printer do the
>interpolating for you. Epsons do a great job here.
>
>Final word - DON'T get your file's ppi confused with the ink dots
>per inch (dpi) that your printer lays down - normally you would set
>your printer's dpi to 1440 for fine detail. For glossy paper, you
>could even use the 2880 dpi setting, although there is debate has to
>how much this actually improves the final image quality, AND it does
>increase your printing time. Printer dpi's (720, 1440, 2880) refers
>to how many dots or squirts of ink your printer will lay down in
>each linear inch of printing. THIS IS NOT THE SAME THING AS YOUR FILE'S PPI!!!
>Hope this helps, and I hope I'm on track here.
>Michael H. Cothran
******************************
Larry Berman
412-401-8100
Art Show Imaging and Jury Services:
http://BermanGraphics.com
******************************
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