Saw doruksal's question about resolution and megapixels on another thread and I thought this might help. I hope I understood his question right...I believe he was asking about prints and megapixels on cameras. I got this info from PCPhoto magazine maybe it'll help a bit.... Using 300 dpi as a standard for printing you would need 300 pixels for every inch of output in both vertical and horizontal directions. For a 3X5 inch print you would need an image file with a resolution of 900 X 1500 pixels to produce a photo quality print. Multiplying those two numbers will give you the resolution you would need from a digital camera.... 900 X 1500=1,350,000 pixels or 1.35 megapixel camera. A 5 X 7 print would be 1500 X 2100 image file. An 8 X 10 print you would want a file with a resolution of 2400 X 3000. For 3x5 and 4x6 prints 1 to 2 megapixels are fine, but for bigger prints like 5x7 and 8x10's a 3 or 4 megapixel camera is better. I'm going to admit that I don't understand this myself completely but it makes sense...however and this is what I don't understand.... if for a 3x5 print you need at 1.3 MP camera then for an 8x10 print you would need a 7.2 MP camera, at least that's the way the math adds up. Maybe someone else can explain that part to me.

I suppose that's theoretical-most find they don't need 300 ppi. Most people, with good 4 MP cams are getting excellent 5 x 7's and 8 x 10's with photo printers--esp. the Epsons (and I hear the new Canons also). If you do a bit of bicubic resampling/resizing in PS or use Qimage to print with (it uses Lanzos interpolation), you will get terrific 8 x 10's. I just printed some 11 x 14 prints from my Oly E10 4.1 MP--I did resample/resize in PS though. The other route is to use Genuine Fractals. In reality, you will get very very good prints with 240 ppi on the Epson photo printers--and many say they get good ones at 180--depending upon the image. Diane

Ok....but isn't camera resolution and printer resolution different things? I usually up my image resolution to 300 dpi before I print....I have the Epson 870...been printing at 8X10 and they look great, at least to my untrained eyes...I've never printed at 240 dpi...although the magazine article I got the information from does say that decent results can be had at 240. With the Epson, I can change the printing resolution to as high as 1440 dpi, which I've been doing....not sure if it makes a difference, or if I'm just wasting ink...but I've been happy with the results. Thanks for the feedback Diane, I wonder if anyone else can add to this.....

Oh, yes, def. Camera resolution is ppi and printer is dpi--quite a different ballgame. Image resolution up to 240 seems adequate, though 300 is 'perfect', but others, as I said, are getting very nice 8 x 10 prints at 180 ppi (that's image resolution, not printer). For the Epson printers, I always print at 1440, BTW. Most everyone on my print forums feels 2880 is wasting ink. I think you mean you are resampling your images at 300 ppi (pixels per inch--that means if you have an image 4 x 6, it would be 1200 pixels wide and 1800 pixels long. If you resampled it to 240 ppi, then it would be 960 x 1440 pixels -altho' it is not a good idea to resample 'down'--resizing and resampling are different though)--the printer is printing at 360/720/1440 or 2880 and that's dots per inch--and with the Epsons it has a lot to do with how the ink is laid down also.

Just thought I'd add--if you have 1600 pixels by 2000 pixels and want it to print 4 x 5, the resolution would be 400 ppi (but the printer would still print 720/1440 or whatever). If you wanted those same pixels to print a 10 x 12.5, then your resolution would only be 160 ppi--and you most likely would see some pixelation. This is where you would want to 'resize' AND 'resample' up to 240 to 300 ppi. Diane

My head hurts! The older Epsons are 1440dpi. They like to be fed an image at 240ppi, so they have 6X6 dots to approximate a pixel. The newer Epson's are 2880. They still like 240ppi, but now have 12X12 dots to play with, so have somewhat (slightly) better dynamic range. [These 6X6 or 12X12 patterns are not fixed, but are "dithered" over a larger area by the printer drivers. But on the average, like to see an integer relation between dpi and ppi.] Most of the dye sublimation printers are 300dpi, but do not use dots of color to approximate a pixel. For best results, really need to know how final result will be printed. But in practice I've found that reasamplin in PS actually works pretty well.

My brother used to work for Epson (back when the Stylus Photo and the 1720 were just being introduced). At 1440x720, printing an image at 150dpi and 300dpi had no visible difference at all (to the naked eye or under a magnifying lens) because of the droplet size. 300dpi was mostly for dye sublimation printing. With the 2880 and the newer smaller droplets on models that came after the photo and 400/600/800 series, though, I'm not sure. - darkpen

if an image is done at 300 ppi, wouldnt any dpi resoultion above 300 dpi be a waste of ink? You won't get a sharper picture, seeing as its the same d/ppi. It you zoome in til you get pixelated, and print it out at a super high printer dpi, it will still look just as pixelated, and no better than if you print it at the actual ppi. Standard commercial prints are 300 dpi. Most print shops won't print any higher, I've asked (this is at least around Montreal). Same with printing text. I know people who swear by printing at 1440 for text... its just text. Unless it's blown up to font zie 200, it won't make a difference. Error diffusion, 300 dpi, glossy paper, fine, and you'll get the same print if you print at 600 dpi... fropm my own personal experience.

Above 300 ppi is sort of a waste, but if you have an image with a great deal of resolution and want to print a small size, that's where you are. No reason to interpolate UP to more than that though. There are some terrific digital printing mail lists. These folks make printing an art---most on my b/w digital print list are shooting with film, scanning with state of the art scanners and printing digitally--for sale. They are interested in producing very VERY good prints--and as archival as possible. Then there are several other lists--some printing with just Epsons, etc. If you are interested in getting the best print with your equipment, then I'd advise trying one of these lists. And then, of course, there is color managment LOL---this will ensure a better print also, though has nothing to do with resolution. BTW, Misha, one of the lists has been discussing the relationship between the pixels and the dots.

mail lists Are these usenet newsgroups, or e-mail exploders? I'd be interested in subscribing.

Misha, they were set up using Yahoo groups--you can read through archives, check the messages online or get them, like the maillists of yore, delivered as posted or digest. http://groups.yahoo.com/group/DigitalBlackandWhiteThePrint/?yguid=1475141 http://groups.yahoo.com/group/EPSONx7x_Printers/?yguid=1475141 http://groups.yahoo.com/group/epson-inkjet/?yguid=1475141 and one for Piezography archival color http://groups.yahoo.com/group/piezography-color/?yguid=1475141

Ughhh....all these ppi/dpi's make my head spin....Misha pass that bottle of aspirin this way please. Thanks for the links Diane.....I'm going to take a look at these too. :~)

I'd search for a site online that discusses image and printer resolutions or look in the help of whatever graphics app you are using (PS, PSP, etc.). Once you get it in your head, its not confusing, but I admit, until you get your head around it, it is smile. Diane

Attached Link: http://www.normankoren.com/Tutorials/MTF.html

Thanks for the links. I'm in some other yahoo groups, and they can be useful. I did some quick surfing this morning, and found one really good tutorial at: http://www.normankoren.com/Tutorials/MTF.html I'm somewhat surprised by the lack of mathematics out on the web, but I suspect when one starts throwing in really non-linear stuff like dye clouds difusion, (or worse, the physiology of vision, or psychology of perception), the math falls apart anyway. I think everyone above is basically in the right direction. The 1440dpi for Epson, or 300dpi for dye-sub printers, are physical constants having to do with the mechanics of the printers. In Michelle's original post, I'd leave everything the same if the image was being printed on a 300dpi dye-sub. Most of the services use dye-subs, so that is why one sees "300" used a lot. If the image was going to a 1440dpi Epson, everywhere Michelle uses "300", I would change to "240", but this is really picking nits. In actual practice, the interpolations in PShop and the drivers work pretty well, so one may not really see any significant difference. In Michelle's #3 post, camera resolution and printer resolution are definitely different things. For a printer like the Epson, you want the printer dpi set higher (about 6X), the camera resolution. I'll need to think about the claim of "wasting ink" by going higher than 6X; I waste a lot more ink in more easily explained muck-ups. [BTW Michelle, I've sent the wineglass tutorial to Alpha, so we'll see what happens. Wine may help more than aspirin.]

Mischa, I think the feeling (expressed as 'wasting ink') may actually be that one really just can't see an appreciable difference between 1440 and 2880 in the Epsons--that's MY guess from the posts I've read. I have 3 Epson printers--one can only print 1440, the other 2 2880, but I stay at 1440--because I really couldn't tell the difference--maybe with a loupe, but not with my naked eye.

Thanks, Diane. I'm never sure if folks are speaking literally or figuratively in the Forum. [Plus, definitions of technical terms like "rawks" and "crepier" don't always get updated in the learning center, ;-) ] From what I've read, there is very little practical difference between 1440 and 2440dpi. It may take more time to print. But if it actually uses significantly more ink I'd be surprised.

????Philosophy is correct, but math may be confused??? >a printer like my Epson 1200 lays down >1440 drops of ink in a square inch So, about 38X38 blots cover a square inch, SQRT(1440) is about 38)? I think the Epson does much better than this. I think the 1440 is the number of blots in a linear inch, same as with the old DPI measurement. >the general consensus seems to be that using > a factor of one fourth the printer's actual > DPI rating will give the best results 1440/180 = 8 ??? I'd agree that this is in correct ballpark. This gives an 8X8 pattern of blots to approximate a continuous tone. I tend to use 1440/240 = 6. Maybe I'll run some experiments also. Now I've invented a new technical term, "blots". Can Slynky top this?

Michelle pops another aspirin Arghhh! I'll just keep printing the way I always have.....resample (is that what it's called?) image to 300ppi resolution and print at 1440dpi on the good old Epson....works for me. Of course this means I'm usually dealing with a 95MB tiff file after resampling, thank goodness my system can handle it with no problems.

Dear Michelle A., Picnic and Alpha...
I'm thankful for all this discussion and all the useful data that all of you have provided.

This weekend, I and a close friend have made some test prints with the Epson Stylus Color 740 printer of his, printing a single "hand-made fractal" image of mine.
The image is a 2-bit b/w image, where you can trace some repetitive shapes till they end up as single pixels.
I resampled the image as 72, 150, 300 and 600-ppi images and saved them seperately.
Then, we printed them at 1440-dpi printer resolution.
What I saw was this: the 300-ppi image resolution was the resolution where a "single pixel of the image" appeared as a "single dot of the print" (not as a visible square, thus not as a pixel), and it made no visible difference at a higher image resolution of 600-ppi (other than a smaller image surely).
"Not seeing 'visible squares' in a print in close inspection" is my practical understanding of a "quality print".
Thus, after our test prints, I arrived at this conclusion: for a quality print, the image to be printed must be resampled at an "optimal" of 300-ppi.
Surely, I do not know how all these work for a printer resolution of higher or lower than 1440-dpi...

As for the "max. desired, min. acceptable" resolution of a digital camera...
It appears that the higher the pixel count, the better and/or the larger the image and print...
Yet, the higher the pixel count, the higher the prices...
So, it's obvious to me that knowing my aims must be the single denominator for making a choice of digital camera: for working for the web, 1.3 or so megapix seem to suit very well; for working for high quality and rather large prints (like 20x25 cm [8x10"]), spend the money (if you have that much)..! :)

Well, from all the valuable discussions that I've read here, and from the test prints that we made, I was able to arrive at such humble, simple and practical (I hope) conclusiuns...
They are suitable..?

I'm thankful...