From A Printers Point Of View

[Toeludeu]

Hi all

I felt compelled to write this after reading some of the posts from you guys on printing requirements.

One question that often comes up when printing digital photos - how many megapixels do you need for a certain size print, such as an 8x10 inch print, an 11x14 inch print, or a larger poster size?

Part of this discussion rests on the quality of the image. If an image is slightly blurry, you may need to resample it to a lower number of megapixels to offset the blurriness, else the quality of the full-size printout may be less than expected.

Printout quality depends on the paper and printer as well. Make sure you are using quality photo paper and not just inkjet or laser paper. Plus, ensure that your printer is configured to use the high-quality paper.

The dpi (dots per inch) of a printout helps determine the image quality and how many megapixels you may need. Generally, the greater the dpi, the clearer and cripser the printout (up to a point). While you can print larger images from smaller digital photos by decreasing the dpi, the results may not be as impressive as if the original image were larger and printed with a larger dpi.

To factor how many pixels you need, multiple the dpi by the size of the photo. Thus an 11x14 image at 150 dpi will need 11*150 by 14*150 pixels, or 1,650 by 2,100 pixels (3.465 million pixels).

Now, with this size, you would think that a 3.5 megapixel camera would handle it. Not so fast! One 3.5 megapixel digital camera actually has an image resolution of 2144 x 1608. While 2144 is greater than 2100, 1608 is NOT greater than 1650! Thus this digital camera, which SHOULD be able to print 11x14 images at a 150 dpi, can't muster enough detail. It's close, but not enough, yet it might be satisfactory for you needs.

Digital camera megapixels and actual resolution (note these can differ depending on the camera):

2 megapixels: 1600 x 1200
3 megapixels: 2048 x 1536
4 megapixels: 2274 x 1704
5 megapixels: 2560 x 1920
6 megapixels: 2816 x 2112 - 3032 x 2008
7 megapixels: 3072 x 2304
8 megapixels: 3264 x 2,468

Pixels needed for a 150 DPI image (fair to good image quality)
----------
8x10: 1,200 X 1,500 pixels - most 2-megapixel cameras

11x14: 1,650 X 2,100 pixels - most 4-megapixel cameras

16x20: 2,400 X 3,000 pixels - most 8-megapixel cameras, maybe some 7-megapixel cameras

Pixels needed for a 200 DPI (good image quality)
----------
8x10: 1,600 X 2,000 pixels - most 4-megapixel cameras, maybe some 3-megapixel cameras

11x14: 2,200 X 2,800 pixels - 7-megapixel cameras, though most 6-megapixels cameras should be close enough

16x20: 3,200 X 4,000 pixels - although this is only 12.8 megapixels, most cameras won't have the same aspect ratio (width versus height), thus you may need a camera with a greater number of megapixels

Again, these numbers are just provided as the results of mathematical formulas. You can resample the image to some degree to make it larger than normal, play around with the printer dpi, etc., and get acceptable larger prints from smaller photos. Just realize that the image quality may not be optimum, though it may be sufficient for your needs

Hope this helps some of you with your printing requirements.....

Toeludeu

[Knopey]

Excellent post! And welcome to AP.

Thanks for the overview, very handy. Just interested in what you do on the printing side, a bit of background about yourself? You certainly know your subject

[Toeludeu]

Excellent post! And welcome to AP.

Thanks for the overview, very handy. Just interested in what you do on the printing side, a bit of background about yourself? You certainly know your subject

Centre Manager for a LARGE print company - bigger in the US than here in AUS, that may give it away

[Craig Miller]

Good job Toe thanks for sharing!

**Sticky**

[Ronnysimulacrum]

I have a question, when I pull the pictures of my 5D and look at the DPI get 72? on all sizes.

I am at a lose to this.

Am I doing something wrong, or have something set wrong?

[Frankman]

Thanks Toe - very informative tute.

The issue of resolution (screen vs print) is one of those that causes the greatest confusion. One question - How can we compare compact Digital Cameras to dSLR's. I thought that dSLR's gave better image quality than (most) compacts at equivalent resolutions.

Perhaps this means that somebody with a dSLR could get away with printing at say150 dpi, whether an equivalent megapixel compact would need to print at 250 dpi to get the same "print quality".

Cheers

[arthurking83]

I've read some info on the relationship between sensors, not the number of pixels, but the size of each photosite on the sensor.

It has something to do with CoC circle of confusion ...

Was only mildly interested on the topic, as I don't do any printing(well one or two for fun).

But, if I can see some interesting results from my shots... I'll look into it more and more, and maybe even get an canvas print made up of something I find remotely interesting

I'll look for the info I found earlier.

[thing]

Again, these numbers are just provided as the results of mathematical formulas. You can resample the image to some degree to make it larger than normal, play around with the printer dpi, etc., and get acceptable larger prints from smaller photos. Just realize that the image quality may not be optimum, though it may be sufficient for your needs

This is a very important if not the most important quote (IMHO) from Toeludeu's excellent & informative post.

I too have worked in the print industry for a long time (I'm too embarressed to say how long) but probably not on the same side of the fence as Toeludeu. My background is prepress, in otherwords it's the stage before lithographic printing where ink goes on paper to be mass produced. Prepress handles all the crap Indesign, Quark, and god forbid Pagemaker files as well as any other crap we get sent from wannabe designers for posters, books, mags, flyers, mailouts, brochures and most of that other rubbish you get in your letterbox and throw out. We also have do deal with all the images included in those files (mostly PS images) and try to make them acceptable.

I think Toeludue is more involved in the short run digital print world but I can't really tell from the post.

I don't want members to think they can't achieve an A1 print to hang on thier wall from a 6mp camera. You can!

Oh one thing I'll add as a tip. If you want to print a photo at a large size (this is generally speaking without much detail) take your original image into PS but go up in 10% increments. So if you want to blow to 150% of your original size, go 10% at a time, not a direct blow up fom 100% to 150%. I often set up an action to do this.