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What resolution and PPI for a picture you want to visualize on a TV?

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  #1  
Old 08-31-2007, 07:22 AM
HenZ's Avatar
HenZ HenZ is offline
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Question What resolution and PPI for a picture you want to visualize on a TV?

Hi all, I’m new on the forum but I’ve been lurking here and there for some info for a couple days (which I didn’t seem to find, except a few answers on this old thread: http://www.retouchpro.com/forums/pho...-tv-sizes.html ).

So here we go, and if any of you have answers, you’re welcome. And if there’s any problem with this new post (not in the good board and needs to get moved, comprehension – I’m French , or anything) please warn me and I’ll do my best to get things strait.

Here’s my problem. I’m working on a project and we want to display pictures on a TV with a mini PC. Actually, I’m trying to figure out the best combo resolution/ppi (ou do you say dpi?) to visualize pictures on an average analogical TV set (you know, the type of TV we’ve all been watching since we are kids) and on these new HD numerical TV sets. I don’t really care about the size of the file for the moment, I’m just trying to figure out the settings that will be appropriate for each TV set (and avoid over-useless-quality) to see a full picture with minimal deformation.

So far, I’ve come to these conclusions, but if someone really competent could confirm my thoughts I would be relieved. Oh: I forgot to precise that this is supposed to be for “French” TV sets (PAL that is).

1- Using JPEG format:
On a normal TV set: 720x576 with 72 ppi (or dpi)
On a numerical HD TV set:
852x480 with 72 ppi for a 480p screen
1280x720 with 72 ppi for a 720p screen
1920x1080 with 72 ppi for a 1080i screen

2- So I’m pretty confused about the ppi displayable on a HD TV: should I put more than 72 ppi?
3- Is there any compatibility problem between 16:9 and 4:3 formats?
4- I’d like to avoid “stretching” problems like, for example, when you have a portrait picture covering the whole screen but being stretched on the sides (let’s say on a 16:9 screen for instance): how awfull is that! How can I manage this? By adding “black stripes” on the sides of the picture? (and do a new picture with the same picture and black parts on the sides?)

This is what comes to me now. I hope you’ll understand my point and wish you a great week end. Thanks for reading…
See you soon.
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Old 08-31-2007, 07:54 AM
pixelzombie pixelzombie is offline
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Re: What resolution and PPI for a picture you want to visualize on a TV?

i've never done anything like that, but i do know you can select the Pixel Aspect Ratio when making a new document in photoshop which will prevent the stretching you are referring to...you could also check out this site as well:

http://www.videohelp.com/
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Old 08-31-2007, 08:17 AM
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Racc Iria Racc Iria is offline
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Re: What resolution and PPI for a picture you want to visualize on a TV?

Quote:
Originally Posted by HenZ View Post
Hi all, I’m new on the forum but I’ve been lurking here and there for some info for a couple days (which I didn’t seem to find, except a few answers on this old thread: http://www.retouchpro.com/forums/pho...-tv-sizes.html ).

So here we go, and if any of you have answers, you’re welcome. And if there’s any problem with this new post (not in the good board and needs to get moved, comprehension – I’m French , or anything) please warn me and I’ll do my best to get things strait.

Here’s my problem. I’m working on a project and we want to display pictures on a TV with a mini PC. Actually, I’m trying to figure out the best combo resolution/ppi (ou do you say dpi?) to visualize pictures on an average analogical TV set (you know, the type of TV we’ve all been watching since we are kids) and on these new HD numerical TV sets. I don’t really care about the size of the file for the moment, I’m just trying to figure out the settings that will be appropriate for each TV set (and avoid over-useless-quality) to see a full picture with minimal deformation.

So far, I’ve come to these conclusions, but if someone really competent could confirm my thoughts I would be relieved. Oh: I forgot to precise that this is supposed to be for “French” TV sets (PAL that is).

1- Using JPEG format:
On a normal TV set: 720x576 with 72 ppi (or dpi)
On a numerical HD TV set:
852x480 with 72 ppi for a 480p screen
1280x720 with 72 ppi for a 720p screen
1920x1080 with 72 ppi for a 1080i screen

2- So I’m pretty confused about the ppi displayable on a HD TV: should I put more than 72 ppi?
3- Is there any compatibility problem between 16:9 and 4:3 formats?
4- I’d like to avoid “stretching” problems like, for example, when you have a portrait picture covering the whole screen but being stretched on the sides (let’s say on a 16:9 screen for instance): how awfull is that! How can I manage this? By adding “black stripes” on the sides of the picture? (and do a new picture with the same picture and black parts on the sides?)

This is what comes to me now. I hope you’ll understand my point and wish you a great week end. Thanks for reading…
See you soon.
Hi, HenZ. I design graphics and images for video and TV professionally for a living. The first thing to consider is that on a monitor of any kind (computer, TV, or HDTV) dpi or ppi is meaningless. The display of image pixels to screen pixels is 1:1, meaning that one pixel in your image is the same as 1 pixel on the monitor screen. It just happens that when an image designed for the monitor screen is compared to the same image printed on paper that the resolution of the screen image is about 72 ppi (or dpi) and so that has become the "standard" resolution of images designed for the screen. And it doesn't matter if the screen is a 13 inch Black and White TV, an HDTV, or even a video projector showing the image on the side of a building. And that's why when designing for the computer/TV screen creating images with higher resolution is just a waste of file size, because it's only the number of pixels that matter.

The other thing to consider is that the pixels of a computer monitor are square, while the pixels of an analog TV are rectangular. This can lead to the slight squishing or stretching of the image if it isn't created with this in mind. The proper pixel aspect ratio for the square computer pixels is 1.0 and the proper pixel aspect ratio for analog TV are 0.9. This is not the same as the image aspect ratio which would be 4:3 or 16:9. It's the actual shape of the pixels. So, if creating an image in Photoshop for analog TV, be sure to choose non-Square pixels (0.9).


Now, to your questions:

1. Format doesn't matter as long as whatever you're using to get the image on screen supports that format. Your sizes and ppi/dpi are all correct, with the addition that 1920x1080 also applies to 1080p.

2. No. 72 ppi is all you need, even for HDTV, as explained above.

3. Yes. Obviously a 16:9 image shown on a 4:3 screen would have the left and right ends cut off. The only way to show a 16:9 image on a 4:3 screen is to scale it down until the width of the image fits in the 4:3 area. This creates those black bars at the top and bottom that's called letterboxing. Another technique to handle this without letterboxing is found on movie DVDs. It's called "pan and scan." Since the whole image can't be seen on a 4:3 screen, when the DVD is created, the 16:9 image is panned left and right as needed to show the most important areas of the image (usually where the action is).

4. Similarly a 4:3 image shown on a 16:9 screen will stretch horizontally to fill the screen, unless letterboxing is added to the sides. The only other option would be to scale the image (without stretching) until it fills the width of the 16:9 screen, but in doing so, a lot of the top and bottom of the image will be cut off.

In this day and age, it is not uncommon to design a couple of different versions depending on the intended medium and display. By far, the easiest thing I can suggest if your image will be shown in a mixed 16:9 HD and 4:3 SD environment would be to design for the 16:9 HD screen, and just let it be letterboxed for 4:3. Most folks are used to seeing this now and probably won't complain if the image doesn't completely fill the screen.

I hope all of this made sense and helps.

--Racc

Last edited by Racc Iria; 08-31-2007 at 11:24 AM.
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Old 08-31-2007, 10:11 AM
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HenZ HenZ is offline
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Re: What resolution and PPI for a picture you want to visualize on a TV?

Hey Racc, i was hoping you to answer my question but not so fast so... i'm delighted with your quick response: thank you very very much. I might have a few questions left, but I'll get these answers update my files first.

And thanks to pixelzombie, I might need that link sooner than I think.

All that made sense and helped!
Best regards,
HenZ
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  #5  
Old 08-31-2007, 11:19 AM
Racc Iria's Avatar
Racc Iria Racc Iria is offline
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Re: What resolution and PPI for a picture you want to visualize on a TV?

Quote:
Originally Posted by HenZ View Post
Hey Racc, i was hoping you to answer my question but not so fast so... i'm delighted with your quick response: thank you very very much.
Wow. Didn't know I had a reputation. ::feels humbled::


Quote:
Originally Posted by HenZ View Post
I might have a few questions left, but I'll get these answers update my files first.
I'll be happy to answer any questions to the best of my ability.

And as you've discovered, this can be a very complicated and confusing topic. It can be difficult to wrap your mind around it sometimes, even for professionals. For instance, everything I talked about above assumes the images are being directly displayed on a screen from the source. If you have to go through another medium (such as a scan converter or a DVD) that can change everything, depending on the capabilities of that medium.

--Racc
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