[ivox3]

This is a very basic piece of information covering dpi and resolution.

The statement, "How do I change the dpi setting to something other than 96dpi in Maxwell so I can produce hi-res images? has appeared in this forum on a number of occasions, .....so this post is in response to that question.

Let's begin ......


If you want something at 300 dpi, ...then you have to tell the renderer to do that.

How ?

First: We determine how big? 4x6 , A3, A4 ....how big (inches/cm's etc do we want the image to be ???

Let's take A3 as an example ...that's 11.7 x 16.5in. right ? ....right.

Okay, ....we need 300 dots-per-inch in everyone of those inches !


Well, ...simple enough, .....I want it to be 11.7 inches in the one direction, ..this I know.

.....so,

11.7in x 300dpi = 3510 pixels. That means, ....in order for there to be 300 dots in every inch, ...I'll need 3510 of them. Okay, ...we have the number now ------ you would enter that into the field for Height. Done.

Next:

Now we want 16.5 inches in the width direction.
Simple:

16.5 x 300dpi = 4950 pixels. Enter that into the Width. Done.

Okay, ....big render ! No doubt and maybe not a good choice for an example. LOL. ..too late.

Moving on, ...
There you have it, .....when that render is done, ....you'll have a 11.7 x 16.5 [A3] sized render at 300 dpi! But ! You say, ....no it's not, ...if I check the properties of the image, ...it says that it's at 96dpi !

Right you are. ....keep reading.


Maxwell outputs files at 96dpi.

The photo editor says that the file is 35.56 x 51.56 at 96 dpi.
Where do these numbers come from ???



Here's the math: Remember, ....even if we change the image size or dpi(same difference) the pixels will remain constant at 4950 x3510.

This won't change if we resize the image to a postage stamp or a billboard .....still 4950 x 3510 will remain, ....but the pixels themselves will change in size and either be very very tiny or very large.



Okay, ...back to our image .....
Using what we know about the image , which is our desired dpi at(300dpi) and the pixels we have to deal with(4950 x3510) we can perform a simple calculation to see the final image size.

** Note: we can use either the height or width (pixels) because we'll assume that we want the image scaled perfectly in both directions.
Most photo editors by default will [maintain proportions] if you change one of the dimensions. Meaning, ...automatically configure the other dimension. Try it and you'll see.

Let's use the width number ... 4950 pixels.




So you can see highlighted in yellow, that indeed, ...if we change the dpi in a photo editor, ...our image has a printable size of 11.70 x 16.50 ! So, ..we weren't stuck at 96 dpi at all ....

For those of you who are thoroughly versed in the subject of resolution and dpi, ...please excuse the simple nature of this info. The intent was to only bring an introduction of dpi/resolution to those who find the subject confusing.

For those of you who seek to understand the concept fully, ....I would suggest, ..simply taking an image into any photo editor and changing the dpi and observing what happens to the size(inches/cm's/mm's) of that image. This is probably the best way to fully grasp the concept.

More elaboration on the subject can be found here:

http://www.graphicdesignforum.com/artic ... sizing.htm
http://www.luminous-landscape.com/tutor ... tion.shtml


ivox.

[lsega77]

ok. I think i understand this but I'll read it a few hundred more time just to make it sink in

thanks Chris....udaman.

Luis

[sandykoufax]

That's good!

Thanks Chris.

[Kabe]

I'm really wondering why this topic comes up from time to time in every graphic forum I've been...

Beside the technical aspect another aspect is often ignored:

Big prints are usually not intended for close view. The eye is limited.
So the resolution that makes sense decreases with viewing distance.

Ignoring this will literally cost you days in production. Producing 300 dpi
instead of 50 dpi means handling 36 times the data...

Kabe

[DavidG]

One way to help get your mind around dpi is to refer to it as ppi (pixels per inch) when its regarding a digital file being manipulated in a photo editing program. PPI is a definition of the size of a pixel using absolute units (inches). A pixel is a relative unit of dimension. That means that an image file that is 3500 pixels wide, well, how wide is it? It's all about how big the pixel is. DPI while still a useful term is hand me down jargon from the days of printing before computers became part of the digital imaging process.

OK so Maxwell renders at a default of 96ppi. Say your render is 3500 pixels wide and 2400 high then those dimensions are absolute, they won't change. However the size of the pixel isn't absolute. We can define how big or small each pixel is so the pixel has to be calibrated against a real world absolute measurement - inches.

If for every inch there are 96 pixels then they are going to be bigger than 300 pixels to the inch. An inch divided up 300 times is going to give us much smaller units than an inch divided up 96 times or 1 time for that matter!

So a 96ppi render at 3500 pixels wide = 3500/96 = 36.45 inches wide
and taking it into Photoshop and adjusting the PPI without resampling = 3500/300 = 11.66 inches wide.

This is all academic so far. Lets make this information useful. If you are rendering for print then you need to start with the last person in the chain and work backwards. Go to the printer and find our their requirements. They may request all files are at the final size at 300 dpi for instance. Your client has requested an A3 print job but of course they don't know anything about dpi or ppi. That's for you to take care of.

So what I do at this point is take Photoshop and use it as a calculator. Create a new document and enter into it the values that you will use, in inches wide and high the dimensions of an A3 @ 300ppi.
Before hitting OK or cancel, flick the dimensions to pixels in the "new document" dialog box and see what they come to. These are the important dimensions, and as someone stated above enter these into your render app as the width and height. So if your render app has a default pixel size of 96dpi, it doesn't matter. You just take it into Photoshop and in the image size dialog box change the ppi to 300 without resampling turned on and the job is done.

[ivox3]

Here is the super simple version:

Let's start off by saying that pixels and dots are interchangeable terms.

If we want to produce a 1" x 1" render with a resolution of 100 dpi(dots-per-inch) ?
[How many pixels or dots will we need to render to achieve this?

Answer:
100pixels x 100pixels Because to meet our criteria of an image that's 1" square with 100 dots-per-inch, ..... we need 100 pixels(or dots) in each direction. People often use dots in place of pixels, and it's not proper, ...we can either get into that later of see the 2 links at the bottom of the first post.

Remember, ...to change the dpi, ....we have to goto a photo editor program for that.

So, ...for any render you want to do .....ask yourself these questions:

1: what purpose will this render be ? The web, magazine, porfolio(digital/hardcopy) ??

After you decide, ......make note of these general settings.
You don't have to understand how these numbers are arrived at, ....for now, ..just know that they're generally accepted standards.
[web images require 72dpi]
[High quality print:300dpi]
Basically, ...choose your resolution.

2. What is the physical size I'd like this image to be ?

Pick a size: 3x5 ? 8x10 ? A3...etc.
Now, ....armed with that info,



3 Take your answers from questions 2 and 3 and multiply them together.

So, ...the new numbers will be how many pixels you'll need to enter in the render settings to have the resolution you need.

When the render is complete, ....take the image into Photoshop/similar and change the dpi to whatever your choice was from question 1.

Voila, .....there's your desired image at the size you want it and the desired dpi.

[ivox3]

Kabe, .....Your absolutely right about large res. images. but I didn't want to personally get into that in the basic course on dpi, ......that's in Chapter 4. :


David, ....thanks for the adding the info. Your right about ppi/dpi, ...and I only made a little mention of it in the above post about the differences and origin.

It's funny, ...at it's root, ...ppi/dpi is a fairly simple concept, ....but it's terribly difficult to explain while maintaing a simple approach. Invariably, ..keeping it simple omits important ideas.

Thanks for the extra info .... Very useful.

[Hervé]

he he.. Chris I am posting this here as well...

Maxwell will always render pixels.... forget the dpi here for now...

First go in photoshop, image size...

resample image ticked ON... constrain ticked off

Now enter any size... like 300dpi.... 50cm x 35cm... (or whatever you need...) and read and take note of the above pixels.. in this case 5906 x 4134... enter these pixels in Maxwell res...

when Maxwell finishes the render, open your render in photoshop, image size again...Now our 5906 x 4134 are still there, but just under it says now 208,35 cm x 145,84 cm at 72 dpi (or your screen res.)
Tick resample image OFF, keep constraint ON... enter 300 dpi... click ok... and voila.. again 50 cm x 35 cm at 300 dpi... simple...

[ivox3]

That's great Hervé and a fine method, but it doesn't expalin the actual concept of dpi/ppi to someone with no notion of it.

I really wanted people to understand the the term 'dpi/ppi' is essentially meaningless and that any image can be made to have 72, 150 or 3000 dpi and how that was arrived at.


The good thing here is that, ......this thread has become a fairly comprehensive discussion of the topic.

[Hervé]

you're right MisterIvox.... he he /// great Hervé... get outta here... ahaha

[Dexel]

Ivox, NL should definitely put an end to your lifelong noncertified usership and employ you to explain all remaining Mysteries of Maxwell in this highly comprehensible style.. in the process you would easily cover most of the remaining mysteries of the human soul as well I'm sure. Nice.

[Hervé]

ok, I vote for Ivox in the A_team and Certified off course...

[ivox3]

Thanks Hervlix.


Dex: Thanks ... but I think you have me mistaken for someone else ..... .....oh the pressure of all that .....
____________________________________________________________
As far as the topic goes, .....it's just one that bothers me, ....It seems to trip a lot of people up. Like Kabe said, ....every once in a while you'll even see it in graphic design forums (what exactly is learned in school?) and of course, ...all the CG forums.

This only tells me that the problem is deeper than what we see with the occasional post/question about it.

It's come to my attention that the basic myth about it is that some think that having a 72dpi image is bad or low quality, while this 'high res' 300 dpi or higher image remains elusive, ...as if Maxwell or other renederers don't produce it. Sounds funny, but it's true. People will actually look at their 72/96ppi image and say, "Now, where's the option or check box for making that image into a 300 dpi ???" or worse, ....they'll take it into photoshop and raise the dpi/ppi from 72ppi to 300ppi, ...and then noticing that the size just decreased (but not reasoning exactly why??) they'll proceed to scale the image back to it's original size ! , ....essentially creating more space for the original pixel count to fill, ...so everything just became pixelated.

Naturally, .....they're horrified at the results.

I know it sounds silly, but people do it everyday, ...hope this combined thread of info moves some people past that errorneous idea.


Thanks all, .....hope I/we didn't confuse anyone further.

[Hervé]

...Hervlix.... pretty trendy... hehe..