Digital images are measured by how many pixels they have.

DPI - dots per inch (or its more accurate cousin, PPI for pixels per inch) - only comes into play when printing. It answers the question "how big do you want this?" by giving a translation between the pixel world of digital images and the inch world of physical media.

Photoshop always specifies DPI, as it is often used for printing images; I use it all the time inside Photoshop to manipulate the as-printed size of my photos and scans without resampling. But if you're not printing, you can ignore it, and focus on the number in pixels. Yes, in some cases you can change the number of pixels indirectly by changing DPI, but it's an indirect connection - and one that can be thwarted or broken (i.e. depending on whether or not the Resample option is checked). Focus on that pixel setting; it's what really matters - everything else is indirection.

In video, all formats are defined by the number of pixels. DPI is never specified. Just think about it: You have no idea how many inches big is the monitor your viewers will be using, and it can vary. What's standardized is the number of pixels, and the display device scales as necessary to fill the desired image area.

DPI may affect print resolution, but it does not affect video resolution - pixels do. So be careful of interchanging "resolution" for those terms.

If DPI mattered to AE et al, it would be in the Interpret Footage dialog (and its equivalent in other programs). It's not. Look at the XML metadata for video formats (not the still image fields; the Dynamic Media fields): no DPI. Look through the ATSC standards for hi-def video (as well a REC 601, 709, and other standards of relevance): No DPI. DPI is (supposed to be) irrelevant to video.

Indeed, AE ignores DPI even when working in "inches": Right-click on the Scale or Position parameters for a layer. Set Units to Inches. The number you see is based on 72 DPI, regardless of the file's actual DPI tag. (I consider that a bug.)

The earliest version(s) of Premiere did look at the DPI for still images, and scaled them based on an assumption that it would use 72 DPI - so a 288 DPI image was scaled to 25%, etc. It dropped that behaviour early on. And as Rick has stated, no other video (or non-vector*) apps do. 

(*Vectors need a DPI-like setting to render pixels. It's like printing in reverse. Nothing to do with video.)

72 DPI is a holdover from the old, old computing days when "WYSIWYG" meant something, and displays strove to represent "actual" size. 72's not a desired target number (our eyes can resolve much finer than that); it was based on the limitations of the tech at the time. Once display and monitor technology improved, it went out the window, with Apple's Retina displays being the latest proof of point. Alas, 72 DPI has stuck with us - but it's irrelevant. (Along with the newer meme that hi def video is 240 dpi, because that's how Canon DSLRs tag their still images. I kid you not; I wasted a few hours with an editor on that one.)

here lies dragons -

Chris

On Jul 20, 2012, at 12:45 PM, Jack Tunnicliffe wrote:

It's certainly an interesting topic, especially now that devices with so called Retina displays are no longer 72 ppi. Who knows what Apple's next AppleTV might look like, a real television with possibly a Retina Display for better resolution than we're used to with traditional broadcast television. For the time being broadcasters will deliver 72 ppi but a television display just like a new generation iPad or Macbook, could display multiple resolutions for different inputs.

Jack Tunnicliffe

Java Post Production

www.javapost.ca

On Jul 20, 2012, at 12:36 PM, Jim Curtis wrote:

I think we're saying the same thing differently.  I'm old-schoold, and DPI is what I'm used to calling it, even though it's been re-branded into Resolution.  

When somebody scans a photo, they usually have an option to choose a DPI, or Resolution.  That has a direct relationship to the number of pixels in the scanned image.  But, ultimately, pixels are pixels.  In Ae, the 72 number is understood, as it's the screen resolution built into Ae.  You can test this by exporting any NTSC frame and bringing it into Ps.  Look at the Image Size in Ps, and you're going to see three numbers: Height, Width and Resolution (which is 72).

I don't suppose you recall a discussion we had with Trish a few years back about using Ae for print work.  What we agreed by consensus was that you could increase the print DPI by multiplying your Ae comp by some factor to get a decent print.

If you wanted 300 DPI, you multiplied your Comp Size by 4.167, which is 300/72.  

So, choose 2550x3300 in Ae to get an 8.5x11" print at 300 DPI.

 

On Jul 20, 2012, at 1:17 PM, Chris Meyer wrote:

I think you might be fooling yourself. I think AE and PR only care about the number of pixels. The way you happened to scale the image - lowering the DPI setting, with resampling on - happens to lower the number of pixels. I bet if you took the same image, and changed the DPI setting with resampling OFF (thereby NOT changing the number of pixels), that you would see no changes in AE or PR. DPI may be a red herring for you.

Or I may be wrong; I haven't re-tested this in years.

 - Chris

On Jul 20, 2012, at 11:51 AM, Jim Curtis <jpcurtis@me.com> wrote:

Yes, as does Pr and Ae.  It's called "Resolution" in Photoshop.  It's intertwined with Height and Width.  If you change one in the Image Size dialog, the other two change along with it, if Constrain Proportions is checked.

Just two days ago, I got some stills that were scanned at 1200 DPI.  They bogged down Pr horribly.  I was having to scale them to 10% to get them to fill the frame.  So, I resized them in Ps, taking the Resolution (DPI) down to 300, and that brought the Width and Height parameters down with it.  Then Pr handled them with aplomb, speedy, and with more workable scale sizes, in the 50-70% range, with resolution left to do panning and zooming.

On Jul 20, 2012, at 12:13 PM, Benny Christensen wrote:

You need to make sure that the DPI is not too high that they are RGB color space. FCP will definitely crash using CMYK files.

I usually resize every thing to 150DPI and no larger than 3000 pixels wide for normal shots or 3000 pixels tall for vertical shots.

I know that FCP is supposed to handle larger files, but this has been safe for me.

Benny Christensen

Producers Playhouse

Oklahoma City

405-858-0700

"I say in speeches that a plausible mission of artists is to make people appreciate being alive at least a little bit. I am then asked if I know of any artists who pulled that off. I reply, 'The Beatles did'." - Kurt Vonnegut (Timequake)

On Jul 20, 2012, at 12:05 PM, Jim Curtis wrote:

Perhaps I should elaborate.  I've been tasked to do a couple of "slide show" projects (Yikes!).  Whenever I brought a bunch of JPEGs in and tried to do Motion moves, and dissolves between them, FCP crashed regularly.  When I brought the same stills into Pr, I had no crashes.  

And on other projects, where I only had occasional stills, I'd still get crashes from the JPEGs, but not after I converted them to TIF.

That's just been my experience.  Maybe it's a codec thing.  I think I'm the Pig Pen of finding things that crash Mac apps.

On Jul 20, 2012, at 11:51 AM, James Culbertson wrote:

FCP 7.03?  JPEGs and PNGs work just fine in my experience. I'm working on a feature length doc that I inherited for finishing tasks that is a smorgasbord of formats - in addition to JPEGs, and PNGs, there are also BMPs, Tiffs,  and PSD. No problems whatsoever. What I would avoid are PDFs.

If I were to choose I would stick with TIFF and JPEG, and use PSD when necessary.

James

On Jul 20, 2012, at 7:12 AM, Jim Curtis wrote:

I've had bad luck with most still formats in FCP.  It's pretty hostile to JPEGs and PNGs, IME.  

Try TIF or TGA, which also support an alpha channel.  TIF is what I use (when I have to.)  

Pr is a LOT better at handling stills, except really large ones.

On Jul 20, 2012, at 8:55 AM, Benny Christensen wrote:

That has been my workaround, but it is annoying because I don't like to use PSDs in FCP. I usually like a flattened file for titles.

Thanks.

Benny Christensen

Producers Playhouse

Oklahoma City

405-858-0700

"To be is to do"--Socrates
"To do is to be"--Jean-Paul Sartre
"Do be do be do"--Frank Sinatra

On Jul 20, 2012, at 8:52 AM, Glen Tubbesing wrote:

You might try using Photoshop's native PSD format, instead.

On Jul 20, 2012 6:38 AM, "Benny Christensen" <bennychristensen@me.com> wrote:

I know this isn't the Photoshop list, but since it is pretty integral to our workflow here goes.

I am having a couple of issues lately.

1) PNGs are not acting the same way they used to. I can't get the empty spaces to read as alpha holes in FCP. Is there a better format to use since PICT files are no longer an option.

2) Sometimes the program simply will not let me Save a file. The Save window pops up, but the buttons are not colored and won't react. In fact, at that point the program is completely locked up and I have to Force Quit.

Has anyone else seen these problems?

Thanks in advance.

Benny Christensen
Producers Playhouse
Oklahoma City
405-858-0700

"Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing ever happened." - Sir Winston Churchill






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