PPI/DPI setting... why do you want it?

-->So, you see, it doesn't matter what you ppi/dpi is, it can be anything you want it to be. The only thing you need to know is what you want your pixel dimensions to be and choose those based upon what your output device is."

That’s true but when you output the file, it’s useful to assign a default output resolution (your pick) so you can print the file quickly and not have to alter this elsewhere (in Photoshop or some other area of a driver).

PowerBook, G5 Mac OS X (10.4.3)

First you need to read this thread about the difference between ppi and dpi[.
http://discussions.apple.com/click.jspa?searchID=-1&messageID=1329138

The same image file has the same amount of pixels and therefore exactly the same amount of detail, it's just that one will print out much larger if you don't tell the printing software otherwise.

1. Any book ordered through Aperture will NOT be printed at 72dpi, regardless of the files you use.
2. As long as you have enough pixels and print out at a reasonable size, that's what matters.
3. Aperture does nothing to files on import other than copy them and read out some info. It's the export stage when things like ppi are set.

Ian

For internal use it doesn't really matter, but send the files to third parties graphic designers or high street labs and they will just see "72ppi" and have a fit.

The vast majority of layout apps will require an additional sizing step after brining the images in as they depend on the PPI setting for the initial size of the image:
Size the image up in Aperture to the required dimensions.
Export, then import into Quark or InDesign.
Now change the output size of all those images because the layout app has a 72ppi image that is 42" wide rather than a 300ppi image that is 10" wide.

I agree it's not an enormous deal, but anything that adds extra steps to the workflow instead of reducing them is a bad thing.

Ian

It's very helpful for design apps to have the PPI set to something reasonable - like 300 PPI for large images. You may resize them beyond that but it's a good starting point.

However what I think people really want is DPI settings along with knowledge of intended size, so the image can be upsized as needed. For instance if I crop a number of images to 8x10's, I would like the final output to be uniform in pixel size.

So in order to really fix the whole PPI thing, I think Aperture should try to keep track of what was selected for cropping and then make note of that when selecting output pixel size at a given PPI.

Currently the only way to upsample when outputting from Aperture is by percentage, which also does not yield a uniform output pixel size. Lightroom does do this by enlarging images (to a point) to be whatever size you want on export, it would be nice to do the same thing in Aperture since it already has the field to let you enter a maximum size - it just also needs to let you say that's a minimu size as well.

I'm a video guy. In video there is nothing but pixels and there is a fixed number of them defined by the video format.
You can make an image larger in video but all you end up with are bigger and blockier pixels; you can't make any more of them (not directly, anyway). You can throw pixels away and make an image smaller but the number of pixels on the video screen never changes. Pixels are pixels.

It's a recurring nightmare with my print people. Doesn't matter what I give them, they freak out. Doesn't matter what I ask for, they freak out.

bogiesan

This is entirly true, Ian. I was wondering why they would have a selection for 3:2 and 6:4 or 4:5 and 8:10 then. I like to think that this is part of a 'resize / upsample' functionality that did not make it into the current version.

André

PowerBook G4 15" 1.67GHz Mac OS X (10.4.3)

I agree with digitaldog.

As far as I can tell, image metadata standards tend to include pixel dimensions and resolution, but not physical dimensions (inches or cm). This can be a problem in paper-output-oriented applications like InDesign, because page layouts exist in physical units like inches, against which your image pixels must somehow be mapped when it is imported. Because image metadata does not include physical dimensions like inches, printing software must derive an image's physical dimensions from something else -- they will normally guess at the physical dimensions by doing the math against the info that is available in the image: pixel dimensions and dpi. If the file is, say, 1600x1200 pixels, and InDesign finds in the image a resolution like 72 dpi, the pixels-to-inches translation results in the file importing on the page at a default size of 22 inches by 16 inches, which is usually much larger than the page! If you are placing a large number of images because you are working on a magazine or catalog, you will go crazy having to resize every image you import. To fix this, when images are destined for print output I like to save files from my Raw, scanning, and editing software at a specific resolution, like 300 dpi (without resampling). That way, when they hit the page, they import at my intended physical size from the start and I can simply keep importing image after image without stopping every dang time just to get a 72dpi image to be smaller than the page. If you can't set the output dpi, you can't set your intended physical size without a trip through Photoshop just to change the resolution.

BTW, it is not true that most printers are set to 300dpi. Many printers, such as inkjets aren't really "set" to anything, but have a native resolution that is some multiple of 120 (360 dpi, 1440 dpi, etc.) Even laser printers passed 300 dpi long ago, now defaulting to 600 or 1200.

I see no reason for a pro app not to allow setting ppi/dpi. A pro app is not supposed to add steps to the process. And anyhow, 72dpi is a stupid default, even as a monitor resolution. Few monitors display that coarsely anymore; most of today's monitors are somewhere between 85 and 110 dpi.

PowerBook G4 15 Aluminum Mac OS X (10.4.3) 2GB RAM

The question remains. What is so sacred about 72 ppi?

Many of my clients have come to expect me to ftp their images cropped, sized and sharpened for final reproduction. They say they get much better results when I handle all of that. I'm billing by the hour for Photoshop type work, so it has become a profit center, and I find that when left to the printer to sharpen files, and oft times even the designer, they do not do such a great job.

So, the ability to export at a given size and ppi is a feature that does not seem at all unreasonable. Telling my clients that their requests for files at 300ppi are unreasonable is unreasonable. It is not befitting of a "professional" program to ask us constantly to do workarounds for such commonly expected capabilities. But it is, like so many other "we know best" features, the Aperture way.

I just took a look at the Print Resolution setting in Lightroom, which defaults to 360dpi. It looks as if it is intended for when a photographer is proofing in the studio to a desktop printer such as an inkjet. Many inkjets, such has the Epson line, optimally print at 360dpi. You would never, ever enter 5760 dpi for your Epson, not any more than your graphic designer clients would enter the 2400 dpi resolution of their prepress platemaker.

Without actually knowing the engineering behind it, I'll guess that this function sets an upper limit for resampling in the case of significantly reduced images, such has when printing contact sheets. The purpose may be to limit the amount of data sent to the printer. When you make a contact sheet of 20 8-megapixel images, if you were to retain every pixel of those images the amount of data sent would be abnormally high, without adding anything to the output quality. If you max each image out at the reasonable upper limit of the printer's input, such as 360 dpi, you only send the data that's necessary, and probably speed up printing.

These applications may be "for photographers only," but the market will probably correct that ideal, to a concept like "but not only for photographers cut off from the rest of the world."

(By the way, every other Lightroom thread in this forum has been "disappeared." The same political fate may await this thread, so we should get back to Aperture, heh.)

PowerBook G4 15 Aluminum Mac OS X (10.4.3) 2GB RAM

Good question David, then I realized that all my
original raw files straight from my camera are 72ppi.
So it appears that Aperture is not changing the
resolution from the original setting. Not sure why
I never noticed it before. So, let's ask around...

<...>

In answer to the question I think a lot of cameras have 72 DPI as a default because they mostly assume the final image is headed to the web. It's just the DPI that makes the most sense for most users, because if users do print consumer printers simply cannot be as persnickety about the DPI as a professional printer.

On the setting of DPI... it's true that Aperture will pass through whatever DPI comes in on the images imported. However if for some reason that data goes missing (or if it was not there to start) then Aperture does set the DPI to 72. I know because my camera has a DPI of 180 by default, and in some cases I have output reset to 72 DPI.

A fix of course is to use an EXIF writer to batch update all master images in your library to something you find more appealing, but I would like to be able to set DPI per export option (keeping 72 DPI for web images and having upscaled images be set to 300DPI).

Here's the scoop.

Early Macs used something called WYSIWYG. That is an acronym which stands for "What You See Is What You Get".

Early Macs had a screen resolution of 72 pixels per inch. Also, the early Apple ImageWriter (a dot-matrix printer) was a 72 DPI printer. This meant that whatever you could see on your black and white Macintosh would be reproduced faithfully on your printer. Verbatim. This set (in a manner of speaking) 72 DPI as a standard for on-screen resolution.

What did this mean? Well, now that images were showing up on screens at exactly 72 DPI, it was a reliable measurement tool for images, so it became normal to create, edit, and save images at this resolution.

By today's standards, 72DPI would be horribly low quality. but think of how things looked in the mid-80's. I remember seeing MacPaint graphics in the San Jose Mercury News - they were blocky, but they looked edgy because they were computer-generated.

Fast forward to the desktop publishing revolution, and the advent of the Apple Laserwriter. This printer was capable of printing at a whopping 300 DPI! (WOW!!!) This printer allowed users to print text and graphics at MUCH higher quality than the old ImageWriter, making it instantly obsolete. Kinda funny how tech works. So hard on the pocketbook!

Well, the Laserwriter made it possible to print at 300 DPI, where the old printers were at 72 DPI. this meant that you could have an image that measured 2 inches square at a resolution of 72 DPI, and it would print out at exactly 2" by 2" on the ImageWriter, but it would be less than 1" by 1" on the Laserwriter. Makes sense, right? The dots on the Laserwriter are much smaller, so the printout would be smaller to compensate.

Now technically, you could print the image on the laserwriter at 2" by 2" just by telling the software (like Photoshop) to do just that. You'd go into your trusty "Image Size" dialog in Photoshop (whatever it looked like on those days) and tell the computer to force the image to be 2" square when it prints. Assuming that your computer and your printer are both in agreement on what an inch is (most are by default), you should be in hog heaven. the printer would just double up its dots and give you a printout that is the same size as the old ImageWriter's printout. Both would look similar, but the Laserwriter would be cleaner because it is a laser printer, and not a dot matrix.

So let's apply this to your current equipment. Most digital cameras capture their images at 72 DPI by default. So when you load them into iPhoto, Aperture, or Photoshop, they look as if they are 72 DPI. No matter what the "megapixel" size is, you're still dealing with 72 pixels per inch. This makes an 8 megapixel image physically larger than a 5 megapixel image, right? Because it has more pixels making up its image.

Your 5 megapixel image is probably an image that is 2592 x 1944 pixels in size. My Canon 20D shoots at 8.2 megapixels, and its image are 3504 x 2332 in size. This means that if I print each of these images at 3" by 5", the 8.2 megapixel image will have more dots crammed into the image per inch. Therefore, it will look crisper and clearer.

This also helps you figure out how big you can print the images. Typically, a 5 megapixel image prints pretty well at 8" x 10". An 8.2 megapixel image prints well at up to 14 inches wide (in landscape setting). This does not compensate for image quality or focus problems, but I have found it to be a good general rule.

Im professional print, you'll se a LOT of 600DPI, 1200 DPI (magazines), and sometimes 2400DPI (for high-end art books). These numbers must be taken into consideration when laying out such publications. My 8.2 megapixel image can be no larger than three inches wide if I want to print it at 1200DPI.

This really does not mean much to all of us who use our inkjet printers, as they tend to blend colors at such high resolutions. I often print 5 megapixel images at 5" by 7", and you cannot really see the difference, the images look great framed and sitting on a hearth or bookshelf. How often do you pick up such photos and look at them close enough to see each individual dot? That being said, your results may vary.

And then there's linescreen - a term that is used in print to describe the coarseness of the dots in images. If you pick up a black and white newspaper, you'll see that the images are made up of small dots. These dots are not pixels, but are in stead called "halftones". A halftone is the term used to describe the way an image is converted to tiny dots, allowing us to print shades of grey using only black ink on white paper.

If you'll look closely at those dots, they are not square. Most are round, or have round corners. This is because ink runs just a bit on paper (especially newspaper - it's called dot gain), but it is also because the human eye perceives images more easily if you don't use squares to build them.

Well, high DPI printers (like 1200 DPI or better) are pretty good at printing halftones. Lower DPI printers are not good at it because the dots per inch of the printer can actually get in the way of the ability of the printer to use those dots to build the little roundy dots in the halftone. So a very high-resolution printer (like 2400DPI) can make VERY perfectly formed and very small shapes, so it is capable of building very high-grade halftones.

One more thing - a halftone was traditionally made using a screen on a camera. This lead to the term "linescreen" or "LPI" (lines per inch). LPI and DPI are totally different. LPI is a measurement of the density of dots in a halftone, DPI is a measurement of a printer, like an inkjet or a laser printer. Generally speaking, the two never meet unless you are using a laser printer or inkjet to create "plates" (printed master pages) for use on a high-end offset printing press. Offset printing presses use halftones to get their images because they use ink, and ink is a less precise art than is most inkjet or laser printing technology.

It's REALLY late, and I'm rambling. I'll let you all go now.

I hope I helped!

--------------------S