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Steve Reeves
06-10-2006, 02:32 AM
Hi all,

Got a quick question here. A lot of my stills I render to print out at A3 size or similar and in all cases I would render out at 300dpi as this is the accepted 'quality' level which gives no visible loss in detail.

As high quality / large format printing has come down in price I am now looking to start printing even bigger - A2 is my next one to try.

Obviously 300dpi copuld be the preferred route and I will do this is if necessary. However I am sure I read somewhere, or more specifically saw a chart somewhere that suggested that the bigger the poster implied the lower the dpi is needed on the basis that the viewer will see the image from further away and so the resolution requirements are less.

This makes sense to me, does anybody agree? Be handy to limit those image sizes from a rendertime and memory point of view.

If anybody knows of a chart that offers a rule of thumb (image size x dpi recommended) that they have used to good effect then I would be grateful for the link.

Many thanks for any thoughts.

Penforhire
06-10-2006, 10:31 AM
I'll be curious if anyone comes up with a good technical reference. I'm sure it depends slightly on the "dot gain" (ink bleed) of the printer and certainly on the subject matter (details versus flat tones versus noise). I know the starting point for viewing distance is the diagonal of the image. So maybe twice the distance allows half the resolution? Stuff on the side of a bus or building gets below 20 DPI.

With the Epson ink & papers I use (R1800 printer) and technical photographs I see only a subtle improvement between 250 and 320 DPI. I can't see any consistent gain above 320 DPI. Like you I aim for 300 DPI as a general rule.

But one of my finest prints was a Super A3 (13" x 19") print of a show car for the owner that started around 240 DPI. I spent some time getting the noise out (Noise Ninja) I interpolated it up to something like 360 DPI (and a 900 MB 8 bit RGB file size!) in Photoshop (just trying some advice from a Scott Kelby book) and resharpened it (Photokit Sharpener). At its normal viewing distance it is stunning. I could have sworn it was going to be disappointing.

See attachment (if I figured out how this forum upload works) for a smaller version of the image I'm talking about.

Steve Reeves
06-10-2006, 11:09 PM
Hi Pen,

Good point about the process resolution. I imagine the capability and technology of the printing process would limit the dpi required by an image to reach its maximum quality output of that process.

I use Photobox here in the UK for my posters - and they do a fine job A3 at 300 dpi. But with your comments in mind I headed off to their website to see what they had to say about it. Bearing in mind that they are geared up for photo printing, their suggestion for 'recommended' dpi (calculated from a table on their website) was 133 pixels for A4 sie and larger. Seems a little low - but a guide for photographers.

For large format they use a Polielettronica Laserlab machine - and to my surprise I learned that it's maximum resolution is in fact 254dpi! Mmmm....and all this time I could have been rendering to 254dpi anyway :D Doh! Can't believe that I have never checked this!

Anyway, what I propose to do, is create my A2 project at 300, sorry 254dpi. And get it printed twice, at 254dpi and 150dpi and see if I can see a difference and if so if it noticeable at viewing distance.

BTW. Nice work with the car - looks great! Is there a bigger version anywhere online?

Cheers

iDV8
06-11-2006, 02:12 AM
133 to 254 sounds very low. You should ask another print shop and get their take on it. It also depends on the paper quality they use too. High dpi on low quality paper is wasted but low dpi on high rez paper is a waste too.
Is the render time long at 300 dpi? Is that the isssue, render time?

Penforhire
06-11-2006, 10:18 AM
Steve, if you go ahead and buy a print let us know what resolution you used and how it turned out.

On that car, I have a 1024 pixel wide version at http://static.flickr.com/22/27019575_e839144e13_o.jpg but Flickr's forced JPEG compromises its quality a little. The sky is not a Photoshop job aside from some saturation, just lucky. The lot's lines add a nice shark-like detail. I used a reflector to throw light on the wheels and modified the color of one parked car at the rear spoiler to maintain contrast. I cloned out some small debris on the parking lot surface too. Lastly the car's dark red color is almost spot-on (hey, calibration and white balance does pay off!). Taken with a D70s and the cheap-but-incredible 18-70 kit lens. Needed a tiny bit of geometric distortion correction using Panotools.