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If you're interested in making your brain turn to slush and ooze out your ear, read this thread about 72dpi resolution: http://tinyurl.com/2pg4xm

Most folks suggest printing at 300dpi - is that for home consumer quality printers or for lab quality printers? Do lap printers have the capacity to print beyond 300dpi?

So let's say I have a 10 mega pixel photo 3872x2592 resolution - if I take this to a lab and have them print that photo to a 4x6, what DPI will it print at? An image of this resolution has the capacity to print a 4x6 at over 600dpi - so if I set the image to 300dpi does the lab ignore this setting and print at 645dpi or whatever the max resolution the photo can support - or does it cut the effective dpi quality capacity of the photo in half and print at 300?

What is the "35mm equivalent" of dpi? If there is one? Assuming 300dpi is the standard, then an 8x10 is the max size photo a 10MP camera could produce?

Thanks,
`S

Interesting question... and I wish I had the answer for you.. most labs tell you to set your file at 300 dpi.. although I use one lab where they tell you to leave it as it is.. funnily enough he is a photographer himself..

As I said I don't have the answer for you... but hopefully someone will..

scottvd wrote:Most folks suggest printing at 300dpi - is that for home consumer quality printers or for lab quality printers? Do lap printers have the capacity to print beyond 300dpi?

The native resolution of the printer is typically measured in pixels per inch (ppi). This is essentially the size of the grid it uses to put pixels onto paper. Each model can have different resolutions, for example:

• Pegasus printers (photo prints up to 20x32"): 250 ppi
• Fuji Frontier "minilabs": 300 ppi
• Canon & HP printers: 300 ppi
• Durst (Lambda & Theta) and Kodak RP30 photo printers: 400 ppi
• Most large-format Epson printers: 360 ppi
• Most "desktop" Epson printers: 720 ppi

The device needs the image data at that resolution, and if you're printing an image at 300 ppi on a printer that uses 250 ppi, something will have to resample the image so the hardware can cope with it. Ideally that would be you with "quality" software, but the printer driver software itself will do it if it has to (although it often uses crappy "nearest neighbour" algorithms when resampling).
If the driver is fed a 360 ppi image and it needs 720ppi, that's just an increase of 2x in each direction: the driver usually does a good job. Thus 360 ppi is often quoted as a blanket figure for Epson printers. And Durst printers can be fed 200 ppi images with good results.

Note that I'm talking about ppi (pixels per inch) rather than dpi (dots per inch) as some printers (e.g. inkjets) use multiple dots per pixel (e.g. Epson printers that are advertised as being 5760x1440 dpi devices). In dealing with the images that we send to the printers, we only care about the pixels, so PPI is the "more correct" unit (although many people use dpi interchangeably, in some situations it means different things!).

So let's say I have a 10 mega pixel photo 3872x2592 resolution - if I take this to a lab and have them print that photo to a 4x6, what DPI will it print at?

To print it at 4x6" inches on a Fuji Frontier (300 ppi) something will have to resample the image (e.g. 1800x1200 pixels at 300 ppi is a 6x4" print). Incidentally, your 3872x2592 image isn't quite the same 2:3 ratio: it would get sampled down to 1800x1205 pixels, requiring a slight crop.

What is the "35mm equivalent" of dpi? If there is one? Assuming 300dpi is the standard, then an 8x10 is the max size photo a 10MP camera could produce?

How much resolution you need in a print is a question with multiple answers!
Does the image have a lot of fine detail that the viewer is going to examine closely? Or with a large print are they likely to be standing further away? The extreme case is of course a billboard, which only needs a very low resolution.
Some people regard 200 ppi as a "rule of thumb" minimum resolution for prints (e.g. a 12x18" print with your file would be at around 215 ppi). You may find with some images you can go lower, and some may need higher. I've got some images I made with a D30 (3 Mp) which printed well enough at 144 ppi (10x15" prints) that I sold plenty of prints.

But once you've worked out how large you want it to be, something somewhere along the line will have to resample the image to match the resolution of the printer being used. Most pro labs tell you the resolution of their printers and get you to do the resizing yourself.

Does that description help at all?

DaveB wrote:Does that description help at all?

Yeah yeah, that was very good, thank you. So DPI is totally the wrong term to use because a pixel can be composed of several dots at the printer side, so DPI values are not an accurate metric from one printer to the next. However, measuring in pixels - PPI is a more stable/universal metric. I see CS3 has provisions for specifying PPI during the crop - interesting.

I read this article on an explanation between the two:
http://www.tildefrugal.net/photo/dpi.php

Ok, all very good - thank you again for your help. Last question, can you make any recommendations for a good online photo processing lab? US presence required! (:

Take care,
`S

scottvd wrote:Last question, can you make any recommendations for a good online photo processing lab? US presence required! (:

Nope, you'd probably be better off asking on a US-based forum. I use labs in Melbourne and Sydney, but haven't had a need to get things printed on the other side of the world.

I gather most of the "online" labs get you to submit your files in sRGB, whereas I use labs that support larger colour spaces and provide proofing profiles so we can check in Photoshop exactly what's going to come out. (Colour Management is a bigger topic than just sorting out the resolution of your printer ). It's a slightly different lab market...

Someone else here might have advice though.

DaveB wrote:I gather most of the "online" labs get you to submit your files in sRGB, whereas I use labs that support larger colour spaces and provide proofing profiles so we can check in Photoshop exactly what's going to come out. (Colour Management is a bigger topic than just sorting out the resolution of your printer ). It's a slightly different lab market...

Someone else here might have advice though.

Dave-
Thanks again for your help.. coloUr management.. yeah, you folks even spell stuff differently! (: I recently got one of those Color Vision Spyder things that calibrates your monitor, very cool.

Thanks again,
`S