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Old Jan 3, 2010, 8:59 PM   #1
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Default having trouble sorting this out - dpi

I've processed a bunch of vacation photos and uploaded them to zenfolio. I was originally only putting them out there for viewing by family members. But, some are asking for prints.

I know they can order prints from zenfolio, but I'm wondering what size image I should upload. I took my original RAW from the K20 image, cropped some, ran through Neat Image (the camera had been changed to ISO800 by my nephew and I hadn't noticed until too late), curves, USM then saved at 12 setting in PSE8 as jpg.

I then went into Image Resize and changed the resolution to 72 and the largest dimension to 800, then resaved at image quality of 4 as jpg and uploaded these images to zenfolio. Some of these images are only 50kb with a size of 800 x 631. When I test and go into the shopping cart to see how large this can be printed, it says I could print this at 5 x 7. If I understand this correctly, they would be printing this image at 114dpi (800/7=114)

Am I understanding this all correctly?

Patty
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Old Jan 3, 2010, 9:39 PM   #2
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Hi Patty
Maybe this info at Cambridgeincolour can help clear it up. I refer to this often in these situations. It explains the processs pretty good.

http://www.cambridgeincolour.com/tut...mera-pixel.htm
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Old Jan 4, 2010, 9:57 AM   #3
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Very interesting website, I really like the picture of the difference in sensor sizes.

I don't do a lot of printing, but I would definitely not resize them that small for printing. Having your largest dimension as 800 is great for viewing on-line but is very low resolution for printing. Since zenfolio is generous with what you can upload (I've uploaded full sized jpg files from the K20), I'd upload a second series of mostly full sized pictures for them to print, then they can decide what size they want. Zenfolio automatically resizes the file for viewing on-line and they seem to do well with their resizing, especially for what you need. Also, I'd save them at the highest quality I could. Of course, then it would help to have a fast internet connection...
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Old Jan 4, 2010, 2:41 PM   #4
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Thanks Rufus, that link helped me clear up some questions I had also.

Patty, just for what its worth. I also use Zinfolio. I usually take all my photos in RAW and convert to Tiff @ 300ppi for PP in CS4. I keep a back up of the original RAW and save the edited tiff with out resizing it for future use in prints. I then re-size the photo to 8"x12" @ 200 ppi which reduces the file size to between 9 and 11 meg. that's the size file I upload to zinfolio and is still suitable for regular prints. If I want to go larger, I go back to the original file @300ppi. Hope that helps.
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Old Jan 4, 2010, 3:39 PM   #5
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You pretty well seem to understand what is going on, Patty. I would not consider that size image suitable for printing, though, even at 4x6. Considerable detail is lost when you downsize that much, and even the best interpolation software can't restore it.
I upload photos of that size to my photobucket account for others to view on PC, but only because I have a slow dialup connection. For printing, I almost always use the full size image, even for smaller print sizes.

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Old Jan 4, 2010, 6:06 PM   #6
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Hi Patty,

DPI when viewed on a computer monitor is a confusing issue, IMO, so I just consider resolution, considering a 1 pixel = 1 "dot". A few years ago, 150 DPI was considered the highest resolution that an average human could discern in a print viewed at normal distance for the size. I actually consider more like 100 DPI about the lowest acceptable resolution for most family photos, and 150-200 as good for even the most detailed of my bird shots. Most magazines and stock photo outfits seem to want 300 DPI or more, but that's really overkill IMO. The best thing to do is to take a nice detailed pic, then downsize and save different resolutions of the same pic. Try to sharpen the downsized files so they appear to have about the same sharpness and contrast on your computer screen, and add text to indicate the resolution so you don't get them mixed up. Then print from each of the files at different sizes, using the same printer and paper, or the same printing service. Compare the prints, and you might be surprised at how well the low resolution files print at 8x10. My experience says that 1MP files (1200x 800 originals at 3:2 aspect ratio) print very well up to this size -- YMMV, of course, and that's why you should test this for yourself. Only you, as the photographer, should determine the minimum resolution for printing one of your shots at any given size.

But bigger is always better, so don't take this as a recommendation that you downsize any image to minimum acceptable resolution before printing. I'm just trying to give you a realistic baseline for acceptable print resolution.

After shooting head shots of all my classmates at my 40th High School Reunion, I posted two sizes of each shot on the web, and included a folder for full res images and another with downsized images on the CD that I handed out to my best friends. Many ended up using the downsized files as they were less detailed, and perhaps a little kinder because of this. . .

Scott
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Old Jan 5, 2010, 5:53 AM   #7
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Patty - thanks for posting this question - I have learned a lot from all the detailed, informative responses!
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Old Jan 5, 2010, 8:28 AM   #8
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My lab requires 300dpi for printing at the highest quality so that is what I always do.

I also crop the the proper size (4x6, 5x7) when I upload them for printing, that way I don't have to deal with the processor cropping them where I don't want them cropped.

Tom
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Old Jan 8, 2010, 2:13 AM   #9
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i work with images and printing for my job
and i still get confused
i doubt anything i am supplied with is 300dpi and i am having to print things at several metres across, some work and some dont
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