resolution...

[rivoli]

So a large billboard can't be printed at 300dpi or else you'd end up with a paper / ink soup!

this is a very good point I never considered before.. must keep it in mind for the next dpi discussion. luckily I don't happen to do that much work for printing these days.

[AJ Jefferies]

Yep the amount of ink is a very important factor, not only is it a physical consideration but it also costs money!

We once had a client who insisted that the black background for their huge poster was 100% in every CMYK channel. Fortunately the printer stepped in & slapped them before things got too messy

[dlparisi]

We once had a client who insisted that the black background for their huge poster was 100% in every CMYK channel. Fortunately the printer stepped in & slapped them before things got too messy

After 100% black (K), what's the point of any other inks? Would there be ANY benefit - like if you added a little yellow you'd get a "warm" black (if there's such a thing)?

[joconnell]

Yeah you often get a richer black with other colours added in.

[AJ Jefferies]

Yep - very few printed blacks are just 100% K.

One of our larger clients actually has 'their own' black - so any & all regions of black in any artwork/photography they use HAVE to be a specific value.

[glyph]

J O'c - that's an april fool right??
the dpi makes no difference to the paper weight
- if you are overprinting 100c 100m 100y 100k it might make it heavy, but the amount of ink at 300 dpi on a bill board would be the same as the amount of ink at 5dpi - bigger dots but same density
(100% black and 60-100% cyan plus maybe a bit of magenta is often used to give nice rich blacks on book covers etc)

[rfellers]

A lot seem to be rendering between 5k & 6k. How long does that usually take to render? When I am working for an architect they usually only have a week or two to prepare for a presentation. That includes them designing the building and me modeling and rendering several views. I currently have three dual-quad computers, but at that resolution it seems like it would still take several days to render the final images. Their schedule rarely allows for that.

For the project I am currently working on, I knew there would be a time crunch at the end (there are 12 images), so to keep the render time at a minimum the lighting is strictly AO with a few spots (no GI). I'm not particularly proud of these images. They are more sketches than realistic renderings. I received only a fraction of the design information the client promised and most of that was given to me very, very late. So the drafts I sent kind of look like sh*t. Now they want a high-res version of sh*t at 5100 pixels.

I did have a client a few months back that wanted a billboard 18 feet tall, 10 feet wide @ 300 dpi. I did the math and calculated about 65,000 pixels tall, filesize would have been 8 GB.

Ryan

[rivoli]

A lot seem to be rendering between 5k & 6k.

I very rarely go over 3k wide. if needed is usually enough to print A4s and A3s. even though, depending on the kind of image, I might go as high as 5k if there are small details that can't be rendered/picked up at a smaller resolution. regardless of what use we'll end up doing of such images, it's more of a quality concern than a printing one.

[dlparisi]

I usually render somewhere around 3500x2400. Lower than that and I feel like there's not enough detail in the images, higher than that and I feel like there's no addtional detail gained. Whether it's my normal texture resolution or modeling details, going higher just doesn't make it look much better IMHO, and actually can make it look more fake as you can see where the digital image starts to break down (kind of like how joconnell described above). When you raise the resolution it seems like your brain naturally expects to see more details in smaller areas (such as scratches, dents, imperfections, etc) and when they're not there it looks less photo-real. It's a fuzzy line for sure but is more of an artistic decision than a math one.

In the past when clients request a 300dpi billboard image (actually something like 6 feet wide which would be 21,600 pixels) I've tried to explain this to them and they really couldn't understand so I simply rendered a higher resolution (something like 6000 pixels) and just scaled it up in photoshop to the 21,000 pixels - NO ONE questioned the quality.

[simmsimaging]

J O'c - that's an april fool right??
the dpi makes no difference to the paper weight
- if you are overprinting 100c 100m 100y 100k it might make it heavy, but the amount of ink at 300 dpi on a bill board would be the same as the amount of ink at 5dpi - bigger dots but same density
(100% black and 60-100% cyan plus maybe a bit of magenta is often used to give nice rich blacks on book covers etc)

I have never heard of DPI being a factor with billboards etc and paper tearing, but the issue of total ink is well known in all print formats. The issue as I understand it is primarily one of dry time between colour passes on the press. Too much ink and you get smearing because it's pooling up too much. Typical printing expectations hold a max black at about 270-290%. Sometimes higher, and sometimes lower.

Printing 4 colour blacks with only 100% black will always read duller than a 4 colour black: due to low reflectivity of paper and dot gain, the black will only read as dark grey.

Resolution for billboards is typically 1/10th to 1/12th of size at 300DPI, so the files required are actually quite small. Printing for large format posters (like transit shelters and window signs etc) often demands a much higher res file. This is due to the point joconnel raised about viewing distance: items viewed up close require a greater dot density to hold up and appear continuous tone to the viewer.

So viewing distance and total ink values definitely are part of the equation.

[super gnu]

A few days to render on 3 dual quads? per image of for all 12? do you use the "universal method"? my renders rarely take over 10 hrs.. on a single i7 w 6 gb...

[glyph]

@simmsimaging: yes I know about total ink and more than 280% causing problems - what I'm saying is a 50% tint of magenta is the identical amount of ink on the paper whether it's printed via a halftone screen of 80 lpi or 400 lpi
its 50% coverage by definition- and solid black is solid black whatever the dots - so the total amount of ink is (more or less) constant - the resolution doesn't come into it

(the dpi is meant to be a minimum of one and a half times the halftone screen resolution .. but I think that's only relevant when using the ultra finest absolute best quality printing - i..e 0.01% of the commercial printers out there )

I had to do 10k renders for a client but we said ok it costs 'x' for 5k and you can have them in 24 hours.. but 10k will be a bit more and will take another 6 hours, so they agreed to go with lower res..
and another time a really low res (real) photo which just had to go into a brochure, to my surprise didn't look that bad at all

[werticus]

I do 4096x whatever it works out to be by default but I'll always ask first what and where it is going to be used in case it needs more.

I call it QUAD HD or Cinema resolution

test renders at 1600x

[zoranm]

I stumbled on this graph some time ago and it proved OK for me.

Red= distance between viewer and image
X= print size (m)
Y=resolution (ppi)
Fuction curve = optimal resolution

It clearly shows how dramatically resolution drops with increased distances.

All this calculations are based on distance between adjoining rods in an eye and how much detail could be destinguished.

Hope this helps

zoran

[Erik de Graaf]

We had this discussion with clients a lot the past years, we always render out the final in 3500 pixels wide for normal print work like brochures. For billboards we double the resolution basically to avoid the discussion wether it is necessary or not, clients are told they need high res files by there advertisement agencies so they go along with it. Billboards for arch viz are never viewed up close so i think 3500 pixels would do fine also.

I've had a discussion with a web developer about dpi a few years back: i asked him what resolution the site would be optimized for so i could render out my images accordingly, he just stated: 72 dpi........
No matter how i formulated my question he just couldn't understand that was not enough information for me. I will remember the mph trick though for future discussions.