1080p dpi?

Hawk Teflon

Hawk Teflon

Veteran
I couldn't find the right forum for this, so please move it if necessary.

I was just told that HD footage is still 72 dpi (I say still, because that's what SD is). If this is true, how is this possible? Wouldn't this be like saying that the quality of HD and SD are the same? That makes no sense to me. NONE! Can you have HD dots? I don't get it.

So I created a new composition in after effects, exported a 1080p frame, opened it in Photoshop, checked the image, and it's 72 dpi. HOW?
 
Video doesn't have a "DPI"... the DPI is based on what you're viewing it on. If you were looking at a 3" wide screen, then you could say that HD video is 640dpi. But if you were watching it on a six-foot-wide screen, then you could say that the exact same HD video was 27dpi.

The # of dots is fixed at 1920. So just change your output resolution to whatever you want it to be.
 
Hawk, resolution and pixel dimensions are two separate things. 1080p specifies that frames are 1920 pixels x 1080 pixels, all the time. Resolution is just that density of pixels per inch/cm/cubit/whatever. It only matters for purposes of output; the effective resolution of, say, a projected image is far different than that of a desktop monitor.

Most pro imaging apps make an assumption around 72 pixels per inch because that's been a standard pixel resolution for many, many years (and is still the assumption on MacOS X, while Windows often assumes 96 pixels per inch). It's inconsequential in most standard video imaging tasks

For purposes of imaging tasks in Photoshop and After Effects, why is resolution - pixels per inch - a concern in the work you're doing? Most pro motion designers and editors effectively ignore resolution as long as the absolute pixel dimensions of their work is correct.
 
atomick said:
Most pro imaging apps make an assumption around 72 pixels per inch because that's been a standard pixel resolution for many, many years (and is still the assumption on MacOS X, while Windows often assumes 96 pixels per inch). It's inconsequential in most standard video imaging tasks
Click to expand...
This is not an assumption that the imaging apps make, this is what they receive from the OS when they ask for device resolution. Someone, 25 or so years ago, measured the size of a "normal" monitor and calculated resolution based on number on pixels on the screen. This value has little use if you are woring with images. It has some use when you develop user interface, it allows to scale the UI when a user changes "screen resolution", another confusing feature.
 



Well .. the screen is ~60 yards wide, that's 2160 inches.

Assuming it's a full-HD 1080 screen (1920x1080)...

1920 / 2160 = ~0.889 DPI

or rather = ~1.125 IPD (Inches Per Dot)

That's some big pixels right there!


- Mikko ... has seen that logo somewhere before.
 
Ok, wow. I think I'm understanding a bit better now.

So if I do, in fact, understand this correctly, a 1080p video on a 40" TV would have a"dpi" (not really, but you know what I mean) of around 48 or so, right? That's less than half of what the SD "dpi" was configured to many years ago on that smaller screen. Yet, it looks very clear. Why is it, then, that people need 300 dpi for print?
 
DPI and PPI

DPI and PPI

The question here is valid as I am also looking for an answer.

There's a misconception in this post that DPI and PPI are the same thing.

Cranky and Hawk:

PPI is pixels per inch and refers to a source images actual resolution based on a camera's (motion or still) image sensor, lens, and processor. In order for prints to come out in traditional 35mm quality or better one must be sure that the photo is at least 300 PPI. When you change an image's size in photoshop it is extremely wise to uncheck the "resample image" box as this will literally change the actual amount of pixels while guessing the color and position of added or subtracted pixels in said image.

DPI most often refers to printer's. A printer that can print 300 DPI is obviously better quality than one that prints at 200 DPI. It just suggests to consumers how many dots of separate colors a printer can fit on a page.

So to make my point and re-post the question... What is the PPI of an individual frame (or image) of most High Definition pictures today? For example, if I took an image/individual frame from Discovery's Life television series in hi-def, and imported that into photoshop what would be the ppi? Of course the resolution would be 1920X1080, but that is the display resolution, not the native image resolution or ppi.

For an example in video of ppi differences here is a video I shot of my daughter's with a 720p high def camera with a very poor image sensor.

http://www.youtube.com/watch?v=JZ7QtK8KnSk

Here is video done digitally with source images of much greater ppi.

http://www.youtube.com/watch?v=wUPcimeiqLE

So, while I'm here to educate a bit, I'm also here to ask. Does anyone know the ppi of high quality motion pictures?
 
atomick said:
why is resolution - pixels per inch - a concern in the work you're doing? Most pro motion designers and editors effectively ignore resolution as long as the absolute pixel dimensions of their work is correct.
Click to expand...
I have follow up to that. I'm saving my images at 1920x1080p at 72dpi in Photoshop, but the gradients in my Jpgs (saved at 100% quality) look chunky; the gradients are not smooth. The gradients loo like they've been saved at 40% quality, if you follow. What's happening?
 
ryanjohnsond said:
I have follow up to that. I'm saving my images at 1920x1080p at 72dpi in Photoshop, but the gradients in my Jpgs (saved at 100% quality) look chunky; the gradients are not smooth. The gradients loo like they've been saved at 40% quality, if you follow. What's happening?
Click to expand...

That likely has to do with file format, if it's 8-bit or higher, other technical crap, less to to do with resolution or ppi.
 
I know this topic is a little old, but it's of interest to me...

I know this topic is a little old, but it's of interest to me...

ulmerster said:
The question here is valid as I am also looking for an answer.

There's a misconception in this post that DPI and PPI are the same thing.

Cranky and Hawk:

PPI is pixels per inch and refers to a source images actual resolution based on a camera's (motion or still) image sensor, lens, and processor. In order for prints to come out in traditional 35mm quality or better one must be sure that the photo is at least 300 PPI. When you change an image's size in photoshop it is extremely wise to uncheck the "resample image" box as this will literally change the actual amount of pixels while guessing the color and position of added or subtracted pixels in said image.

DPI most often refers to printer's. A printer that can print 300 DPI is obviously better quality than one that prints at 200 DPI. It just suggests to consumers how many dots of separate colors a printer can fit on a page.

So to make my point and re-post the question... What is the PPI of an individual frame (or image) of most High Definition pictures today? For example, if I took an image/individual frame from Discovery's Life television series in hi-def, and imported that into photoshop what would be the ppi? Of course the resolution would be 1920X1080, but that is the display resolution, not the native image resolution or ppi.

For an example in video of ppi differences here is a video I shot of my daughter's with a 720p high def camera with a very poor image sensor.

http://www.youtube.com/watch?v=JZ7QtK8KnSk

Here is video done digitally with source images of much greater ppi.

http://www.youtube.com/watch?v=wUPcimeiqLE

So, while I'm here to educate a bit, I'm also here to ask. Does anyone know the ppi of high quality motion pictures?
Click to expand...


The answer to this is: there is no inherent PPI for HD motion picture. In fact there is no inherent PPI or DPI for any digitally stored images. You simply cannot have a PPI without a value for I. Because there is no standard for display sizing, there is no standard number of inches that a 1080p image should be displayed at.

There is a pixel size (1920x1080 for Full HD) and sometimes (in the case of certain file types) you may have a target PPI/DPI for the image, that is to say, a display device or printer may be instructed to scale the output to emulate a particular dot density, which may be more or less than the device natively has, this is when interpolation and anti-aliasing come into play. For digital images PPI/DPI is purely a property of output.

In the case of your example videos, both are being displayed at the same physical size (presumably on your monitor) and the lower quality image is being scaled up (with the gaps interpolated across the space) to match the same physical display size of the higher quality.

This is currently a very interesting point in mobile application/web development as devices may have the same size (for example the iPhone @ 3.5") but different PPI (160 for iPhone3G or 326 for iPhone4).
 
ulmerster said:
The question here is valid as I am also looking for an answer.

There's a misconception in this post that DPI and PPI are the same thing.

Cranky and Hawk:

PPI is pixels per inch and refers to a source images actual resolution based on a camera's (motion or still) image sensor, lens, and processor. In order for prints to come out in traditional 35mm quality or better one must be sure that the photo is at least 300 PPI. When you change an image's size in photoshop it is extremely wise to uncheck the "resample image" box as this will literally change the actual amount of pixels while guessing the color and position of added or subtracted pixels in said image.

DPI most often refers to printer's. A printer that can print 300 DPI is obviously better quality than one that prints at 200 DPI. It just suggests to consumers how many dots of separate colors a printer can fit on a page.

So to make my point and re-post the question... What is the PPI of an individual frame (or image) of most High Definition pictures today? For example, if I took an image/individual frame from Discovery's Life television series in hi-def, and imported that into photoshop what would be the ppi? Of course the resolution would be 1920X1080, but that is the display resolution, not the native image resolution or ppi.

For an example in video of ppi differences here is a video I shot of my daughter's with a 720p high def camera with a very poor image sensor.

http://www.youtube.com/watch?v=JZ7QtK8KnSk

Here is video done digitally with source images of much greater ppi.

http://www.youtube.com/watch?v=wUPcimeiqLE

So, while I'm here to educate a bit, I'm also here to ask. Does anyone know the ppi of high quality motion pictures?
Click to expand...
First off, you're absolutely correct.

It's been a long time since I studied this stuff, 11 years actually, but back then at least anything created for the screen would have 72ppi.

This was in 2001 though and a lot has changed since then. Even if I still had my text books somewhere and could check, they would be too old to be relevant these days. Wouldn't you need to import the raw video file unaltered straight from the camera to photoshop to figure that out? I would assume anything else is still 72ppi.
 
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