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Hi guy's. Looking for some help here please. Not about glass but digital for a change.... Could somebody please tell me the difference between DPI and PPI and how it works to achieve a crisper finish at a large size in Photoshop. I don't do a lot of digital work but always wondered how these differences work. I recently made this design for a company in Connecticut, they asked me to make it at 10ftx8ft which I did at 72 dpi working at full size. I know of other designers working at 400 dpi at quarter size and probably other calculations. My computer started slowing down at 200meg file sizes adding effects and fades took a while but I got to the end ok. I have made designs in the past at 4ftx4ft working at 100dpi and the edges are very clean but I know there is a formula for ppi which would probably work out better.
It maybe time I guess to upgrade my 2 year old computer as processing power and other parts are probably way more advanced now and make processing power quicker. This is the design which is being used for a backdrop at a Cigar show in Vegas next week.
Thanks
Dave
Dave, I'm not the expert here, but I'll chip in with my crude 2c as no one else has replied yet...
PPI is the picture resolution of a bitmap file in a photo editing program like adobe photoshop, corel photopaint and others.
It's for pixels (a pixel is a PICture ELement) per inch, of file size.
Suppose your file was a picture one inch square, with detail or resolution of 25 ppi, there would be 25 x 25 = 625 bits of data for the computer to memorise the location of, if it was saved as a Tiff file for instance.
That's where vector files (corel draw cdr, adobe illustrator ai & eps) are useful, as the file crudely consists of the mathematical formula for the outline, plus a formula for the colours of the fill or contents. It can be infinitely enlarged with no loss of clarity, and the filesize is small but accurate. (That's as long as bitmap files or effects aren't embedded in the vector file- that increases the file size).
Back to PPI- most monitors display pictures at a resolution of 72 ppi- that looks good on screen, but can be fuzzy if printed out at that size & resolution.
With digital files, they're going to be output on a machine that is capable of spitting out so many drops per inch of cartridge travel, so you can get 200 or 350 or 600 or 1200 dpi pictures. You'll be flatoout telling the difference between the upper levels with the naked eye- frequently even 300 dpi is clear enough for most purposes.
You can have a file of 72 ppi resolution, [which contains 1/4 as much data as one of 144 ppi (as it's 1/2 length x 1/2 width)], but you can still print it at 600 dpi- that'll kind of give you a fuzzy picture, with very nice gradual tone variations. It'll look 'clean' and not so fuzzy.
I've found that to do nice clear pictures to be enlarged to billboard size like 8ft x 16 ft. and which have to be tiled (printed in 2 overlapping strips), that it's been good to design the file at 300ppi, but at 1/4 of life size, i.e. half the length & half the width.
The printer then rips that to print at fullsize, and at 1/4 of that resolution, i.e. 75ppi- but they'll print it at 600 dpi, and it'll be really nice.
Even finally saved as a jpg, the file will then compress down quite a bit, and be OK. I've had files of 500 meg per half, or per tiled strip, and then when all layers are merged and the file saved as a jpg, it can become about 64 meg. It'll still reopen as a 500 meg file though.
However, if you can do the file in say corel draw, or flexi, or illy, and add photo elements & textures underneath the text & vectors, you'll keep clarity high, and file size low in comparison with making it all a bitmap or picture file.
As for any formulae you ask about- I don't know any, except that 1/4 size, at 300 ppi has been good for me as a designsize if doing it in photoshop Your 10 x 8 ft pic at 72 PPI should have been fine.
It's all a matter of juggliing computer capacity, your time & expereince & the software you have, and knowing the final intended output viewing distance & purpose & priinter specifications, plus the client's budget.
You always need to design with the intended finished article in mind. You won't be successful of you designed a digital file at 72 ppi to go on a 1 x 2 ft door magnet, then the client decided to get it enlarged to an 8 x 4 ft shop sign- it'll blow up inexcusably fuzzily, as that size & resulting resolution was not reckoned upon in the original file.
There are workarounds, and some software that will enlarge poor pictures remarkably well, but as I said, this was all meant to be a crude simplistic summary!
Hi Dave,
For at least "most" practical purposes, I think DPI (Dots Per Inch) and PPI (Points Per Inch) are essentially the same thing.
A critical issue for your purposes is the optimum LPI (Lines Per Inch) for printing or output. For example, many glossy printed magazines are set up as 133 to 150 LPI. Newspapers and coarse paper are only 85 LPI and high quality art books and prints are 200 LPI. An EDGE printer is roughly 75 LPI at best.
The old formula is to create artwork two times the LPI AT THE FINAL SIZE. So, a magazine might request 266 DPI at the size they are going to print. If the magazine is 9" x 13" and you were printing the full page, the image would be 9x13 at 266 DPI. If you were going to send someone a file for an EDGE printer, you only need to send a 150 DPI at let's say 3' x 6' if that is the size of the image. Any resolution over the needed size is basically unused and just wasting memory. A single layer (flattened) image at that size is 167 megs in RGB. The same image at 300 is 667 megs. If you are working in layers in Photoshop, each layer might be 667 megs. Saving to a JPG can compress it, but that compression is "lossy" (degrages). When opened in PS, it will be back up to 667 megs.
In short, the answer to your question is really "what is the output device?...and what does it need?" You really need to know that before you begin. You can always design at a higher resolution, then reduce if your hardware can handle it. Going up in size will give you a degraded image.
Good luck,
Mike Jackson
Mike Jackson / co-administrator Golden Era Studios
Vintage Ornamental Clip art
Jackson Hole, WY
OOps, I forgot to mention that- those LPIs are Lines Per Inch, and refer to the frequency of the dot 'screen' used in making halftones, for screen printing, or newspaper & magazine & printed photos.
Denver Chapter of the Letterheads