I saw on the Renderosity home page about them asking for renders to use in advertising etc.

One question I did not follow is the 300 PPI - pixiels per square inch. Thats something I am more familiar with in the definition of a monitor. - I figure it means the same thing for a render - but how do you know if it meets that criteria or how do you set the Rendering engine to meet that? - which is probably the better question.

Thanks
EWS

I think they mean DPI (dots per inch for printed matter) rather PPI but it kind of amounts to the same thing.

If you decide on physical size you want the image (say 6 inches by 4) then render to disc you can set resolution to 300dpi.

or you can just calculate image size out using brycetech's handy guide...

http://www.brycetech.com/tutor/bryce/bryceinprint.html

I had a long discussion w/ Jason about that and I don't get why they specify it at all, other than to let people know that when the images are printed, they'll be tiny unless you render lots of pixels.

it's like you've commissioned a chef to cook for a banquet and have said, "we'll be serving rice in half-cup serving sizes," but neglecting to say how many people are attending the banquet.

when I asked about this, I was told that there is no minimum size for images.

also, after a bunch of back and forth, he said, "we want to avoid people submitting images at 72 ppi," but that's silly, IMHO - since he had said that he'd resize images if necessary.

when I've rendered images for print, I'd create a new file in Photoshop at the correct pixel size and the "resolution" set at 300.  then I'd open my render (most apps render out to computer-screen-viewable defaults of 72 pixels per inch, but that's another red herring as well), select all, copy, and paste it into my 'for print' document.

the whole ppi thing is a bit of a fiction.  it's a flag in the header of the digital image file that controls what the output device sees.  in Photoshop, for example, go into the Image Size dialog, make sure the "Resample Image" checkbox is NOT checked, and then change the 72 to a 300.  when this is done, the INCHES change, but the PIXELS remain the same!!

If you are using the services of a professioanl printer, at least this is true for the printer that I use; there is DPI information in the image's header that tell the presses how to interpret the size of the image.
In other words, if I take a 3000x1500 image @ 100 dpi to the printer, I get a 30"x15" print back (and it looks very bad). The same image @ 300DPI, and I get a 10 X 5 print back (that looks about like it's supposed to).
And I have to use CYMK colors too, instead of RGB.
Could be different for other printers, don't know for sure.

DPI is completely irrelevant for web graphics or monitor display. Normal web graphics are 72, sometimes 96, DPI. It's all about image resolution (total pixels) divided by screen size in that case, the PPI.

exactly right calyxa. ppi is only a trigger to tell whatever program how to size the image. 300 dpi (or enough pixels to correspond) is an appropriate number of colour points to allow for the use of four offset screens in commercial image printing operations. 

excellent example dvlenk6

dvlenk6: excellent example.
 
I've always read that Higher DPI is better for images that will be printed.
 
100-150 DPI are supposed to be the ideal resolution for BubbleJet / Injkjet Printing anything higher is good for Professional printers.

However recently I've gotten a bit confused about the entire matter.

5 MegaPixel Cameras produce 2000+ x 2000+ Images at 72 DPI.   I've always been told 72DPI is the desired resolution for Screen display as the file size is smaller and you dont need the unneeded resolution if you are not going to print them.
 
However when these photos are printed at a Digital Printing services like at Wal*Mart the 4x6 Photos are pretty sharp and hard to tell that they came from a Digital Camera.

Higher DPI settings on a Digital Camera would probably introduce new problems. i.e. Higher Processor and Larger Memory would be required to handle the larger file sizes.

let's go back to the rice analogy.

when you're looking at rice cookers, does it make sense to ask if a particular rice cooker can cook rice in half-cup servings?

what matters is the maximum capacity of the cooker itself, or how much rice you've made this particular time.  it is only when the rice is actually dished out that the "grains of rice per person" affects how many people you can serve out of the amount of rice you have cooked.

when you're looking at digital image creation tools (digital cameras or various rendering applications), it doesn't make sense to ask if it can create images at various "pixels per inch" -- what matters is the number of pixels that you capture or render.

just like the number of servings you'll get out of your rice cooker, it is only when the image is printed that the pixels per inch required by the printer (grains of rice per serving) tells you how many inches you'll get (number of servings) out of the number of pixels you have captured or rendered (amount of rice you have cooked).

in dvlenk6's example, a huge pot of rice has been cooked.  in the first case, we've served up 300 people with a tiny amount of rice each and they're all unsatisfied (printing 30 inches by 15 inches at low quality).  in the other case, we've served up 100 people with a reasonable amount of rice each (printing 10 inches by 7.5 inches at high quality).  in both cases, it's the same amount of rice!

it's highly unlikely that a digital camera will include a "pixels per inch" setting any more than a rice cooker will include a "grains of rice per serving" setting, except perhaps as a convenience to the end user.  far more important is the maximum capacity of the device - the total number of pixels it can capture or render, or the total amount of rice it can cook.

Quote - I've always read that Higher DPI is better for images that will be printed.

The printer shop I normally use when I need printing jobs done will not make prints of anything less than 300 dpi.
Unless I'd flat out demand it of them, I suppose then that they probably would do the job...

Well you could render at a lower resolution and then blow it up to a larger size, but you're losing detail that way and making things pixelated or fuzzy. (Not exactly great for print.) If you want a nice sharp and crisp image, render at or slightly higher than the dot pitch being printed. Of course how much this matters also depends on intended viewing distance. You could probably get away with 72dpi for something like a poster to be viewed from 10ft away, but that'd look cruddy if it was at that resolution for a picture in a magazine page 1/4 the size because now it's viewed at less than arm's length.

Thanks all ! I feel informed and the printing part makes a bit of sense here. Though I did not know that Renderosity actualy dealt in any hard copy material - advertising side of things.

Thanks Gog for the link as well.
EWS

I've been following this thread and now ICM has linked this solicitation fm RR in another thread.  I don't understand the request of 300dpi if  there is no corresponding finished image size constraints.  Or am I still losing out on the dpi debate?

Will not a 300 dpi render that is 3000x3000 result in a 10inch x 10 inch print that was printed at 300dpi?

Will not a 100 dpi render that is 3000x3000 result in a 3.3 in x 3.3 in print that was printed at 300dpi?

Will not a 100 dpi render that is 3000x3000 result in a 10in x 10in print but be of a lesser quaility?

If my assumptions are correct, should the 300dpi requirement not need a finished image size stipulated also?

I think they are specifying the 300 so that your image doesn't get shrunken when printed.
3000x3000 printed at 300 dpi will yield a 10" x10" high quality printed image. The original dpi (render) is of no meaning in this. 3000x3000 printed at 100 dpi will yield a lower quality 30"x30" printed image.

3000x3000 pixels doesn't change, no matter what your ppi/dpi settings are - it'll always be 3000x3000.

ppi is a file in the computer - the actual pixels - 3000 pixels by 3000 pixels.
dpi is a printing term - it's how many dots per inch are actually PRINTED by a machine.

We use them loosely - interchanging in day to day conversation - and in speaking in terms about the size of an image, they mean the same thing. I think Rendo was just being technically correct in what they asked that you send - it's a digitial image file so hence the ppi terminology.

And Incarnadine is right - look at your pixel sizes - 800x600 is TEENY - 2400x3000 is nice and big. The ppi/dpi doesn't mean squat until you actually go to print. Just make sure your pixels are enough to cover the sizes they want to print.

Hope this helps-
-Lew ;-)

The ppi/dpi doesn't mean squat until you actually go to print. Just make sure your pixels are enough to cover the sizes they want to print.

@ thundering1

My point exactly,  RR is requesting a 300dpi but not the desired print size.  That additional info would be necessary to submit a suitable image.  Am I not correct?

To say we need pics rendered at 300 ppi/dpi is not info enough. That's called... "The horse, bridles from the back."...
They should also say what  the resolution(s) should be .
 
Example:
20in x 20in would be 6000 x 6000 ppi/dpi...right?

That additional info would be necessary to submit a suitable image.  Am I not correct?

Bingo! More often than not, I just wish they (Rendo, clients, etc.) just gave you the pixel dimensions they want and skip the dpi altogether. the dpi is the 3rd part of a 3-part equation, and it means the least. Kinda frustrating.

20in x 20in would be 6000 x 6000 ppi/dpi...right?

Yep - exactly!

-Lew ;-)

a 20"x20" image to be printed at 300 dpi would be 6000 pixels x 6000 pixels. what rendo is doing is advising you that if you submit an image its pixels will be divided by 300 by the printer and that will determine the printed size of your image. They just don't want you to be surprised that the image filling your monitor will be less than a third of that size when printed.

for example, you have your proverbial 1600x1200 pixel image (my monitor size). the image fills my 20" screen at its resolution. However, when printed using 4 colour offset at 300 dpi the image will be 5.3 inches x 4 inches in physical size. Given that size reduction i am going to be dissappointed with the loss of a lot of detail. This is what rendo is trying to avoid.

The client should specify what the image will be used for, it is always wise to do the work planning for 300 dpi printing even if they ask for a lesser requirement. you can always resample down a copy (archive the master).

They rarely tell me what they're gonna use it for - I just give them the biggest files I prepare. I find my stuff in catalog (medium sized 300dpi - though it's printed at 150 lines), as well as magazine ads (full page at 300pdi - again, printed at 150 lines) and newsprint (name that size - 150 -125 dpi printing).

On the VERY rare occasion, I've had images on billboards - 36 dpi.

They print in so many different media I have absolutely no way to contact every printer for every job and find out specs. I just give 'em big files and the graphic designers resize them smaller to fit whatever it is that they're putting together - that's THEIR job, not mine. Mine is to give them sufficient sizes to do what they want - and they'll call me if they need it bigger.

-Lew ;-)

Ok! Someone please make my head stop spinning!

Must... End... Techno-babble... Sorry guys!
-Lew ;-)

hey thundering1, been there too, though most of the time i was on the printing/graphic arts side.