Render quality/size

[Josh Lloyd]

I am just curious on what size and resolution everyone typically renders at. I have pretty much stayed to 11x17 size at a 300dpi. But it I was to just the image up to say 24x36, would you reduce the dpi at all?

Most of the stuff I do is for print. But it is for sit down meets. No big presentations yet.

[Stephen Leworthy]

i generally render out at 2000x1500 px. this is pretty good for most sizes.

This is quoted from Jeff Mottle in a previous post -


Basically when you are printing/rendering an image you have three variables to consider:

1. DPI/PPI (Dots per Inch/Pixels per Inch) Both are the same thing and are also known as resolution.

2. Pixel size - measured in pixels (this is normally what you render to andiis how monitors are measured.

3. Print size - measured in inches (can be anythign but I'll use inches for convinience)

1. DPI/PPI

First you need to know what resolution your printer can handle. Some will say that they go to 1200 dpi or 600 dpi, but in practice you should never need to go bigger than 300 dpi, even if you are printing a 60 ft wide billboard. Just like digital camera's non-optical zoom abilities, printers use DPI to claim superiority in the industry.

DPI is the number of dots of ink that are put down by your printer onto a page over a one inch line. The amount of resolution that a printer can achive is based upon how close together the print head elements or jets are positioned. Of course it is a bit different with a 4 color press, but for now I'll just leave it at that. You may also notice that your inkjet will say that the vertical resolution will is different than the horizontal resolution. This is becuase in one axis the printer is relying on the proximity of the jets to each other, whereas the oher diection is related to the sensativaty of the rollers that are feeding the paper across the jets.

2. Pixel Size

I'm assuming that everyone is pretty familiar with pixel size as we deal with is on a daily basis. However, don't assume that your print house will be, because in many case they are not. You will usually need to give them an image size in inches based upon the resolution that their printer is capable. Don't try to explain it to them becuase they just won't get it.

Pixels are something that your monitor uses to describe the very small square dots (pixels) of light that are lit up by the guns of your CRT. (LCDs are different) Typically we say that a monitor is 72dpi.
A pixel translated to a page is usually represented by many dots of ink depending upon the print resolution.

3. Print Size

This one is pretty self explantory and is the image size on the page that your printer printed.

So you know what each one is but how do they relate to one another? As I mentioned earlier there are thee variables in this equation. To get one you must have the other two, so here are the possibilites:

For these examples let's assume that our printer is capable of 300dpi I am going to print an 8 x 10 image and my rendered pixel size is 3000 x 2400

You have Pixel Size and DPI and want image size:

This is useful when you want to know how big an image will print on your page if you do not allow the printer to scale the image at print time. (ie scale to fit).

===========================

Image Width = Pixel Width / DPI

Image Width = 3000 pixels / 300DPI

Image Width = 10 Inches

Image Height = Pixel Height / DPI

Image Height = 2400 pixel / 300 DPI

Image Height = 8 Inches

You have Pixel Size and Inches and want DPI

This one is not all that useful and I can't think of any reason to use it practially but here is it anyway.
========================================

Horizontal DPI = Pixel Size (Width) / Inches (Width)

Horz. DPI = 3000 pixels /10 inches

Horz. DPI = 300DPI

You can use the same equation for the Vertical DPI as well. Some printer are the same resolution in both axes.

You have Inches and DPI need pixels

This one is usful when you know that your printer can print 300dpi and you would like to print an image that is 8 x 10 and need to nkow how big to render your final image to do this. Of couse you could always render it bigger, but rendering time is precious so you never want to render more pixels that you have to.

=======================================

Pixel Width = DPI x inches (Width)

Pixel Width = 300 DPI x 10 inches

Pixel Width = 3000 pixel wide

Again the same formula can be used for pixel Height as well.

So now you know what each variable is and how they relate to one another. The biggest hurdle I suspect is how they relate to one anotehr visually, but that will have to wait for my DPF document.

Hopefully this helps some of you and does not confuse you even more. Even if you do not fully understand the why yet, you will at least have the formulas so you know how.

[Evert Vandenberghe]

As our printer (the guy, not the machine) prints at 254dpi, so we make everything at that resolution at the required scale (minimum A3). It's big/large:
A3 = 42cm x 29.7cm at 254dpi gives you 4200x2970 pixels

rgds

nisus

[Stephen Leworthy]

nisus - i understand exactly where you comming from but hey, 4200x2970 for A3 printing?

man, you must spend ur life waiting for renders to finish printing at A3 at 1/2 that pixel size would look almost identical!

[Pavel Roder]

As soon as you are not looking at it under lens-glass it LOOKS identical

[Evert Vandenberghe]

As we devellop all our prints like photo's, this IS noticable... Why do you think we don't do GI, but stay close to max3.1 fake? ;-p

rgds

nisus

[Edward Sine]

Years ago, before the color printing technologies we have today, the only way I could get a high quality print was to send to a service and have a negative made from the file and then have photos made from the negative. Their required file size was 5000 pixels wide.

I have found this to be a fairly good guideline for rendering resolution to this day. My clients ask for all different sizes of prints, so even though it is overkill for a small print, you can still get a good large format print from the same file. In response to your other question, I have found that a minimum of 100 dpi will still produce a good large format print (24x36). The 5000 pixel image will usually work fine.

Another consideration is to render as high as you need to bring out the details in your image. You will also find that an image rendered at a high resolution and reduced in size will be sharper than an image rendered at the same smaller resolution.

[Stephen Leworthy]

Originally posted by Ed:
You will also find that an image rendered at a high resolution and reduced in size will be sharper than an image rendered at the same smaller resolution.

are you sure about that or just hypothosizing? sounds fine in theory, but i'd seriously doubt that statment.

[Edward Sine]

I originally read about the concept of downsizing several years ago in some publications about animation. They suggested rendering at twice the desired frame size and downsizing by half to create animation with sharper detail. I tried it, and to me it did seem to be better. Even though I don't normally use it for animation projects because of time constraints, I do use it on print projects. Personally, I can see more detail in the images, and with today's fast processors, there isn't that big a hit on the final render time of a single image. Also if you plan to add plants or other detailed items in Photoshop afterwards, the higher resloution will allow finer detailing and control.

[John Dollus]

With animation, that technique is used to soften hard edges and improve on low quality render settings. For print, you are only interpolating pixels and creating blended edges with the reducing technique.

I generally render out at 100% physical size and half the dpi resolution of the target printer. Then again, I print everything out on a Lambda anyway which makes pretty much everything look great.