 Kerby Pfrangle |
DPI What is DPI? I want to know 300 times 300 pixel with a 72 DPI how many kbs or mbs is that? What is DPI mean?
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Brenda D. |
Kerby hope this helps , and congradulations w/ Kodak http:/www.mycamera.com/index_glossary.cfm
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Michael H. Cothran |
"DPI" stands for "Dots per inch." It is actually misused in digital photography. It is a term originally used for offset printing presses, and represents how many individual 'dots' of ink the printer lays down per linear inch. The correct term for digital printing is "PPI", which stands for "Pixels per inch." Related to your image file, it tells you how many pixels your image contains per linear inch (the more the merrier - to a point). A quality image file that you plan to print should be saved at 180 ppi or greater, preferably 180, 240, or 360 ppi if your printer is an Epson. Anything less than 180 ppi becomes questionable as to image quality, and anything over 360 is simply overkill. Note - your monitor is set up to view @ 72 ppi, awith some newer monitors displaying @ 96 ppi. The printer, itself, would be set up to print (lay down) a minimum of 720 dpi, and preferably 1440 dpi, which, in this case, would refer to the amount of 'dots' of ink your printer will lay down per inch. Hope this helps. Michael H. Cothran
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robert G. Fately |
Kerby, Michael's answer is pretty complete, except for a slight error about the printing part. The resolution of printers varies, but is generally around 300 dpi. Some go higer - Epson's are 360 (and for some of their small printers, 720) and others lower, but no printer actually works at 1440 dpi. That inflated number is more of a marketing trick - it refers to the smallness of the ink droplets that are sprayed onto the paper. The true determinator of resolution, though, is the printer driver - that is, the program that translates the numbers in your digital image file into the image you see on paper. These drivers are specific, but can handle resolutions other than the "ideal". That is, even though the Epson driver "likes" 360dpi, and the Kodak dye-sub driver "prefers" 301dpi, the reality is that you could feed both printers a file of, say, 240 dpi and get outstanding results.
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Richard Lynch |
Just to expand on what Michael said: You need to tune your PPI to your printer/output device. I have seen requirements anywhere from 72ppi (monitors) to 800ppi (high-resolution negative/transparency output) at final size. But printing can be high to low ppi, for example, image plotters use as little as 100ppi for poster/large format printing. Most normal quality printing is within the 240-305ppi range, and that will satisfy most home printing and press needs. The actual file size of the image will vary depending on compression types, file types, number of colors, etc., so a definitive equivalent in file size isn't really possible. Hope that helps! Richard Lynch
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Richard Lynch |
Bob, Some printers go over 1440 dpi...though likely you won't be using them at home. Printing presses are often 2540 dpi or better. For much of home use, you are right though...the 1440 refers most likely to the fact that there may be 7 inks jetting dots onto your paper at a potential rate of 1440 TOTAL...that is, each with only a resolution of 205 dpi/color. I guess what I should say is: there are a lot of output devices and configurations, and understanding how to use image resolution with a specific output device is far better than trying to have one universal solution. In my book I have a small chart of possibilities...You need to be familiar with the manufacturer suggestions (and sometimes even those need tweaking).
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Kerby Pfrangle |
Brenda, Michael, Bob and Richard, http://www.blairhoward.com/contests.html Actually I wanted to know for this contest. The rules say 300 times 300 pixels and 72 DPI. My mind works more in kbs and mbs and I needed it converted. The man running the contest wrote back and said that it should be no more than 100 kbs. That is so small to me but that the size I sent in. I sent in a picture last week and won his contest but I am not sure what size I sent in and this week he said if it not the right size it would be disqualified. So I had to figure out what size he wanted. Thank you for your responses. I really appriciate them. Kerby
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
That's an image size. Just like you resize for uploading. A square 300x300 pixel image, save it so the file size isn't bigger than 100kbs. Save it at your highest setting, if it's 200kbs, have to save it again at a lower setting until it's 100kbs. Resolution 72dpi.
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Richard Lynch |
Kerby, Looks like whatever you did previously was just fine as you seem to have won the dramatic Light contest on Blairhoward.com. Congratulations! I assume you want to enter future contests with confidence in your sizing. I am going to oversimplify a bit, but here's what to do in the future: 1. Open the image you want to ue for the contest. Be sure it is RGB (check the Mode). 2. Choose Image Size from the Image menu (Image>Resize>Image Size). 3. Be sure the Constrain Proportions box is checked, check Resample Image, and set the sampling type to Bicubic. Don't close the dialog yet. 4. Look up at the Pixel Dimensions panel. Choose the higher of the two numbers and change it to 300. NOW click OK. 5. Choose File>Save for Web. In the Save for Web dialog, choose JPEG, and push the Quality slider to 100%. click OK, and save with a different name than the original image. While images will vary by a few K one way or another, you will often be under 100K with these steps. If not, you can tell at the bottom of the Save for Web preview. If the file size is too large, just lower the quality a little till you get it under 100K. Hope that helps! Richard
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BetterPhoto Member |
"You need to be familiar with the manufacturer suggestions (and sometimes even those need tweaking)." What does that mean, exactly? I've got an Epson Stylus Photo R1800. Does that mean when I go to print something I should always print it at a specified manufacturer DPI?
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Richard Lynch |
Manufacturers don't always define what is best in their literature as they may be creating specs that are better for sales than actual printing. A sad but true scenario. For example, some may say they can print an 8x10 from a 1.5 MP image, and then claim high DPI -- if you have high DPI, then you will want more image information to make use of it. Printers have an absolute DPI that doesn't change--the smallest dot that the printer can make defines the maximum printer resolution. The specs for that machine are a little confusing, as there are 8 inks and 5760x1440 resolution. I would guess that means the actual DPI for the printer is 180, with a 1/4th step pass (in other words it is actually 1440x1440, but the motor doesn't move a full step). Somewhere along the line manufacturers started saying the total number of dots was the resolution -- one dot per color -- so the numbers for printers that have more inks are usually more impressive, but less realistic. According to the calculations I usually use, you should be using between 180-240 DPI in your image file because of the efficiency of inkjets. I would lean toward the upper end of that except in the case of large image prints, and even then I might upsize the image with interpolation. What resolution does Epson recommend for your images going to print?
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BetterPhoto Member |
You see, I really don't know. I'm just starting to learn all this stuff. I have a 7.2 MP camera so I wanted to make a few 13" x 19" prints. Should I use 180 DPI for prints that big? When do I use interpolation? Is interpolation the [Resample Image] checkbox under the [Image Size] window in Photoshop CS2?
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Richard Lynch |
The result you want is a little too large even for that number of pixels. You can try it and see what you think of the results, but I would do one print to see if you like the results before doing too many all at once. Different people like different results...I am a technician and I understand the numbers of it--and how those numbers achieve optimized results. Sometimes I find that prints that are not optimized are acceptible -- it really depends on the subject matter and the expectations I have for the result. I err on the side of correct proportions. make sense?
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BetterPhoto Member |
I'm sorry. (*^_^*) When you say, "The result you want is a little too large even for that number of pixels.", do you mean my 13" x 19" should print with less DPI (the result being larger dots on the print) or more DPI (the result being the larger DPI number) than what I stated? "Sometimes I find that prints that are not optimized are acceptible..." Where can I find the numbers (i.e. what is optimized for what kind of print) that you refer to? I appreciate your patience.
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BetterPhoto Member |
Could anyone else please offer clarification? Thanks.
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robert G. Fately |
Matthew, maybe this will help you understand. There is much confusion about resolutions and what means what. First, understand that a color printer has a "native" resolution; this is specified by the manufacturer. For the Kodak 1400 dye-sub printer, that resolution is 301 dpi. For your 1800, it's most likely 360 dpi (the smaler Epsons are usually set for 720 dpi). Now, all this talk about 1440 or 2880 dpi is marketing poop - this is the theoretical resolution when taking into account the extremely small (picoliter) droplets of ink that the head "spits" at the paper. But the printer driver - the piece of software that translates your image file into a form recognizable by that particular printer - "thinks" at 360 dpi...when the printer does its thing it spits out those teensy ink droplets at an overall resolution of 360. Now, this would mean that ideally you should present the printer driver with a file set to 360 dpi for optimal results. Of course, if you send it a file at 180 or 240 or 507 dpi then what it (the driver) does is converts that to the 360 "needed" by the machine itself. And frankly, the resuts are often not that bad - so it's not a high crime to use other than the optimal resolution. That said, the comment about your desired image size "being too large for that number of pixels" is a bit off the mark as well. This is because digital images are more conducive to upsizing than analog images that have been scanned. In other words, unless you try to go too crazy, you can in fact upsize your 7MP image to a larger print size. Photoshop's ability is pretty good here - yes, using bicubic interpolation - you might find it best to upsize about 10% at a time. That is, let's say you crop an image and it ends up being 10x12" at the desired 360dpi. You can use the upsizing function in Photoshop - just set it to change size 110% a few times over, and for most images that should be fine. Alternately, you could get a program like Genuine Fractals, which is designed specifically to make better upsizings (if you want to go more extreme, say to poster size). Either way, just remember to not do your final sharpening until you get to the size you desire - artifacts from the sharpening function will tend to look bad if they are enlarged. I hope that makes some sense...
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Richard Lynch |
"When you say, "The result you want is a little too large even for that number of pixels.", do you mean my 13" x 19" should print with less DPI (the result being larger dots on the print) or more DPI (the result being the larger DPI number) than what I stated?" Your resolution and the amount of information in the original document will be a little low for printing 13 x 19. ""Sometimes I find that prints that are not optimized are acceptible..." Where can I find the numbers (i.e. what is optimized for what kind of print) that you refer to? " The calculations are in my book. The numbers for inkjets are calculated approximately by the following: (PrinterDPI / #inks) x [1 to 1.4] A four ink printer that claims 720 dpi would be: (720 / 4) x [1 to 1.4] 180 x [1 to 1.4] = 180 to 252 ppi in the original image. This equation may not hold for all technologies and all printers, but it should be close.
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