how can increase the output DPI

[Gianfranco780]

hi guys, i'm new on vray, I'm using Vray for rhino and i want to know if is possinle increase the dpi of my output file .
so far i can see that i can go out with a render immage on 96 dpi, but i need to increase this to 150 how can i do that?
I need to do a poster 3 by 2 meters

[thomthom]

Re: how can increase the output DPI

The DPI is a result how how many pixes in size your image is in relation to how large it will be printed.

3m = 118,11"
2m = 78,74"

In pixels given a DPI of 150
118,11 * 150 = ~17716px
78,74 * 150 =~ 11811px

However, do you really need 150DPI for a huge 3mx2m poster?

[Gianfranco780]

Re: how can increase the output DPI

i would like to print it in 72 dpi , i think that will be good but do not have idea of how set the output file in order to have a good quality and i was see if ther is a possibility to increase the dpi and than in photoshop rescale the immage, can you help me please

[thomthom]

Re: how can increase the output DPI

The DPI reported in Photoshop when you go to Image Size is simply a guidance.

The actual DPI you get when printing you find by taking the number of pixels and divide by the number of output inches.

If you have an image that is 1000x500px and print that on a 20x10" paper - the resulting DPI is 50 (1000 / 20)
If you print the same image on a 10x5" paper - the resulting DPI is 100 (1000 / 10).

In the case of your 3m x 2m poster in 72dpi - you want to find out how many pixels you need:
118,11 * 72 = ~8504px
78,74 * 72 =~ 5669px

The DPI value embedded with images are simply a guidance for application controlling how large it should print. However, with layout applications like Photoshop, Illustrator and Indesign, you specify on screen how large you want the image printed - which makes the DPI value to be ignored.
What matters is how large you want to print and how high quality you want - you then calculate how many pixels you need to achieve that.

This is the link I send around at the office when people ask about DPI:
http://www.rideau-info.com/photos/mythdpi.html

[thomthom]

Re: how can increase the output DPI

Note that scaling bitmap up, beyond their original size never does any good.
In other words, you can't render small in V-Ray and scale up in Photoshop thinking you'll get higher resolution. (Sorry if you know this already, but it is a misconception that often occur and I write it here in case someone who doesn't know this reads this thread.)

[Gianfranco780]

Re: how can increase the output DPI

thank you , you really blow out my consusion on this subject

[robbo_cg]

Re: how can increase the output DPI

Hi All

I think the question should be ,how do we alter the settings in VRAY to give us a larger size document but maintain a high resolution.

Any one got any samples or idiots guides to this important but not well documented subject

Robbo :

[frip51]

Re: how can increase the output DPI

Gianfranco,
recently, I ran into a similar thing, here's my thread: click me!

There are two options for such ultra hi-res renders:
- render to disc
- use DR with multiple slaves

...or combine both...


But I agree with you guys, it would help a lot if we had a dpi selector field.
Or maybe there's just a formula behind that computes the pixel size from dpi and english/metric dimensions, if needed.
It could look like this one:



;D Photoshop rocks.


Cheers,
Matt

[LeoBonilla]

Re: how can increase the output DPI

but if that is done, does V-ray has to change to render salve and to render to disk automaticly? i think that with making the calculation separatly is better. That way you won't blame V-Ray for not rendering a huge image and suffereing of memory allocation.

[frip51]

Re: how can increase the output DPI

Leo,
you could have both, I guess. Render to disc using DR (and therefore multiple discs to render to ).
I don't blame V-Ray for anything in the process I simply had to find out how to cope with those massive amounts of pixels...

Separating prepass from rendering is a neccessity in this case.
Producing a 13228x6614px image (2799,93x1399,96mm @120DPI), I did a 3000x1500 prepass to disc, saved as .vrmap and started a 12000x6000 render using DR. In Photoshop, I edited the final resolution to fit the print shop specs and did some colour correction for output. And there it was - a 9ft wide banner!

I just had to play a while figuring out to which minimum initial file size i could shrink the model.
I ended up with the _exportRenderMesh/export to .obj/re-import routine Micha came up with a long time ago. Did that with every object in the scene, the result was a 16MB file (original 55MB) and it worked out perfectly!


Cheers,
Matt