 Stephen R |
Too many pixels? Using 300ppi as a target for inkjet photo printing as is widely recommended, is it not advisable to print 600 or 700ppi images? Printing a pic with 2400 pixels width at 4x6" is 600ppi, and wonder if that's OK or should be sized down nearer the 300?
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William Schuette |
Hi Stephen, you are mixing up ppi (pixels per inch) and dpi (dots per inch). PPI is the resolution of your file. This will depend on your camera's resolution and the size at which you are attempting to render the image assuming you have not used some program to uprez the file. DPI is the number of dots produced by the printer per inch and its highest resolution is limited by the brand and model of you printer. When printing you want to make sure that you have a sufficient file resolution (ppi) to produce a print with dpi that appears to the viewer to be a continuous image and not like an old newspaper photo. Generally, I have heard that HP printers work best with a 300 ppi image, Epson best at 320 ppi for color and 360 ppi. Printing at higher resolutions is not going to improve your print but unless it causes your printer to do something funny, I don't think printing at a higher resolution will cause any degradation in print quality. Bill
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doug Nelson |
Want a pictorial lift? Check out Bill's portfolio. Makes you want to go out and do photography. Check with your printer mfr to find out the best input resolution. 300 pixels- per-inch going into the printer is a safe assumption for most consumer grade printers. My 5 year old Epson prints fine at a 240 ppi input resolution. An excessively large file doesn't cause any problem I know of. I see no need to size it down before printing. The printer's advertised dots-per-inch figure doesn't mean much, as the eye can't detect dots on prints (unless you attempt to print larger than your file size will allow). To see what you can get from the file size you have, open it in Image/Image Size (PS7's terms). Uncheck Resample and enter the Image Length. The image width and resolution will be calculated for you. If the resolution for the print size you want drops below about 240, you're looking at settling for a smaller print, or at res-ing it up with a program that fakes the bigger file size you need.
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Stephen R |
Thank you both, though Bill, I'm not sure I follow. About the ppi and dpi, if image file is 2400x3600 pixels, and you print a 4x6" isn't that 600Ppi image-printing res., regardless of what the printer's dpi may be? Say 1440x5760 like my SP1400. If you make print 8x12", now you're at 300Ppi, closer to mfr's and most recommendations. I print betw 206 and 360 usually 240-300 range. On larger, 11X up, I often try to resize w/o interp. for a printing-ppi target that's a ratio with printer res. Using 1440dpi here, a 4:1 ratio would be 360ppi, 6:1 is 240ppi, etc. As you say those high PixelsPI are not undesirable for those small prints with 600-800 PPI printing-res., good to know, thank you. Any idea if ink usage rises as well?
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William Schuette |
Stephen, no matter what your file resolution is, the printer can print only up to its maximum dpi based on the brand and model. When you resize a file without resampling, you change the physical size of the image but not the numbers of pixels; therefore, if you increase the size but have the same number of pixels your pixel denisty or ppi is reduced. Conversly, if you downsize the image without resampling you get increased ppi. Since having extra ppi is probably not going to cause any problems, downsizing doesn't usually affect picture quality, However, up sizing can significantly degarde picture quality if the ppi gets too low. This is why you have to resample when you upsize. But you are adding pixels that weren't there when the picture was taken which creates its own loss of quality which is why you would not want to up rez a file and then print at smaller sizes. To prevent any degradation from unnecessary up sampling, I always keep my master file in its native resolution and size then make a seperate file that is either up rezed or downsized for a particular print size and paper. Finally, printing a higher resolultion file should take no more ink than using your printer on its finest setting. Hope this helps. Bill
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John G. Clifford Jr |
There are two reasons most people print at 300 dpi: the human eye can't see a difference if you print any higher, and that is the printer's native resolution. I print on Epson inkjets, and their 'native' resolution is usually a multiple of 360 dpi, so I tend to print at that resolution and up- or down-rez my images accordingly. Look at this earlier thread for more information on dpi and image resizing: http://www.betterphoto.com/forms/qnaDetail.php?threadID=29896
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