Understanding resolution and pixels

[chow choppe]

hi guys

 

i am trying to understand resolution and pixel dimensions.

if i save an image of size 1200 pixels at 300 DPI from 3ds max and take it to photoshop and make it 100 dpi and 3600 pixels will the quality be same?

 

actually i am trying to render a big billboard size which is 186 " wide and rendering it at 100 dpi means 18600 pixels which is huge so i was thinking if i save image at 200 DPi and reduce pixel size to 9300 from 3dsmax and then enlarge it in photoshop will it be same as rendering 18600 at 100 DPI?

 

thanks

[Ismael]

http://forums.cgarchitect.com/74294-render-resolution-4m-x-2-6m-sign.html

[RyderSK]

With such logic we could render at 1x1px and milion DPI and just extrapolate infinite resolution in Photoshop ;- ) DPI is purely print stuff, it's absolutely irrelevant in regard to resolution.

 

18k is absurdly high, but so is 100DPI billboards, when most billboards aren't printed with more than 25DPI.

 

Even then, DPI=/=PPI (Pixel per inch density) doesn't need to match. You can print with 25DPI (and they most likely will, regardless of what the supplied image will be) and image could literally be 10PPI. Yes, even fullHD render can look good on billboard, it's super blurry anyway and no one stares at it closely. The overlayed text can be much higher PPI but images don't.

 

From different perspective, 18k render is on very high side, but justly doable. Just lower your AA Sampler settings by a LOT. Lower it by x0.5 for every resolution doubling from 2k/FullHD. GI can be pre-computed at 1/4 of final resolution just fine.

 

But read Ismael's link first :-)

[Justin Hunt]

also most printers dont look at the pixel dimensions they are only concerned with DPI and print size, some of them dont even look at that and only look at file size, which makes no since at all.

[chow choppe]

okay

 

now i dont know what is wrong. reading that link and doing the calculation. 18600 at 100 DPI is 6200 at 300 DPI?(18600/3)?

when i open this image in photoshop and try to expand now the image size showing is 20 inches and i enlarge it 3 times it only becomes 60 inches and not 186 as calculated which means my calculation is wrong somewhere. please help

[Zdravko Barisic]

Do not mix DPI and size in pixels, they are not connected at all.

Size in pixels, is apsolute size, so it is as is. End

DPI is just "agreement" you made with printer device.

Egz:

1800x1200 is fixed, right?

By changing DPI, you just change the Dots Per Inch, for printer.

It can be 18x12cm, or 180x120cm, whatever you want.