GoofyNewfie wrote:
DPI (Dots Per Inch) and PPI (Pixels Per Inch) are two different things.
Not that you have to do it, but you can't even set DPI in Photoshop, only PPI.
You two responders should do yourself a favor and read something about the subject here:
http://www.uglyhedgehog.com/t-147932-1.htmlYour math is right for this rough guide but the unit you used is incorrect.
BTW (By The Way) A lot of inkjet printers typically print at 1440 DPI and higher.
Well Goofy,
This subject has been argued 'till the cows come home, and nothing is going to resolve the argument.
You are correct in your statement,
"DPI (Dots Per Inch) and PPI (Pixels Per Inch) are two different things."Technically they are different values and identifiers.
A Pixel is a tiny light sensitive transistor that converts Photon energy into electrical energy. AKA Picture Element.
A Dot is a spot of ink squirted onto a sheet of paper.
PPI refers to how many photosensitive transistors can fit onto a specific sized photosensitive chip. If your photosensitive chip is 1 inch long and the transistors are small enough to fit 300 lengthwise into the chip you will have 300 PPI.
DPI refers to how many ink dots you can cram into 1 inch of paper, and still render details. In days of old, newspapers would print photographs using dots of ink, and we could count the dots that made up the rendering of the image.
The same holds true today in giant highway advertising signs. Sitting in your car, driving down the freeway at 65 MPH, you can see the contents of the sign clearly.
If you stopped and climbed up to the base of the sign you could not clearly see the contents of the sigh for all the dots making up the content. The farther you get away from the sign, the more the dots blend into a nice rendering of the advertisement.
What this all boils down to, PPI can be used to gauge the resolution of a device to capture an image electronically, digital camera to computer. DPI can be used to gauge the resolution of an image to a printer. Fortunately, technology has evolved to the point where the transistors on the photosensitive chip are close enough to the ink jets of inkjet printers to be equal. Our modern consumer printers perform the required calculations to convert the PPI values to DPI values to obtain the best quality printed document within the standards of current resolutions.
When it comes down to providing image products in the 'Real World', we must supply the imagery products in the format and resolution values the customer requires. If the customer wants DPI because his professional level printers require that value, we must provide DPI in the image product. Failure to do that and the customer will most likely say, "Very nice picture, but we cannot use your content."
Another area of contention is images on the WWW.
If you take an image straight out of the camera, save that image as a .jpg @ 300PPI/DPI, then go back to the camera image and save this image as a .jpg @ 72PPI/DPI with a modified file-name. Now, using your computer navigation tool read the file details for file-size on both image file-names you will see the 300DPI is much larger than the 72DPI file.
This may not be important if you only send pictures in e-mail, or upload to web servers in New York, and all your visitors/contacts live in New York with 100Mbaud internet connections. If you expect people in the rural countryside, who still have dial-up internet accounts, to view your web pages, or read your e-mail, they will delete your ultra slow content.
There are people in other parts of this world who pay for internet service by the bandwidth. The larger the image file in Mbytes the greater the bandwidth, and the more cost to that user.
Facebook is another good resource for viewing images uploaded in high resolution. Facebook re-sizes and resets the resolution according to internet standards because its content is available world wide. If you upload a high resolution image to FB, the rendered image may look poor on all monitors because FB uses a computer to automatically convert your high res picture to internet standards without regard to rendering quality.
If, on the other hand, you take the time and effort to re-size your image to what FB wants, and to 72DPI, FB will render your image to the highest level quality your computer can display.
A case in point in the medium we are now using. When we post an image to this forum, the server downsizes the image resolution to the WWW standards for rendering on a common computer system (your home computer). The server may also re-size the image to fit into the page format. The image thumbnails appear almost instantly when we open a post.
On the other hand, when we post an image and tick the "Store Original" box, this places a link in the post to download the original image file in its native size and resolution. Notice how long it takes to render that image on your computer. The higher the bandwidth of your internet service the faster the image will render on your monitor.
In the USA, most ISPs charge for the bandwidth service provided (5Mbaud - 100Mbaud), not for the bandwidth consumed.
So, once again it depends upon the end use of the images, as to how we save each image. In the early 1980s the internet industry agreed that a picture saved at 72DPI was the lowest resolution that could produce a high quality rendering on a CRT monitor. That value has not been revoked.
Michael G