Quality of Images in Slideshow affected by Down-res

[Ron P.]

First I want draw attention to the following advisory:
Private Emails and Messages to Forum Staff.

I received the following PM:

On the post titled 'can I select photo resolution?' you replied with the following - 'It makes no difference what your image sizes are, once you insert them into the program, and create an SD (Standard Definition) video, then the images are down-res'd to match.'.

My question isn't about size but rather quality. Would the end result of what I see on my TV via a Picture Show slideshow be of a better quality if I scanned my photos in at 600DPI versus the standard suggested size of 300 DPI? They say that for making enlargements of a photo, say a 4x6 to a 5x7, that you should go use the 600DPI setting, but printing the same size or smaller to use 300DPI.

On one hand 600DPI is a higher quality than 300DPI, but on the other hand they suggest 600DPI only for enlarging existing pictures and yet you state that Picture Show downsizes them. Would the better picture quality make a difference?

Simple answer would be no. The reason is that DPI, Dots Per Inch does not apply to viewing on a monitor or TV. DPI only applies to paper, that's it, nothing more.

Television and computer monitors use PPI (Pixels Per Inch). So if you have an image that you scanned at 600dpi, and want to view it in a slideshow on your TV, and your located in an NTSC area, and you're not creating an HD video, then your image is going to be 720px X 480px, that same image scanned at 300dpi is going to be 720px X 480px.

So printers use DPI, while PC monitors and TV use PPI. They do not relate to each other.

[melkisadek]

Having read the beginning of this thread I think this is where I need to be to pursue the issue of slide resolution just a bit further. My Microtek i900 scans with ppi settings that range from 150 to 3000 (approx). If I understand what I read above, PictureShow will downres whatever I "feed" it. And I can live with that. My question is . . . what's the native resolution that PictureShow uses. I might as well scan at that rate and save some time and computer energy . . . yes??? Oh, and I've been saving my color slide scans as jpegs, is there a better format to use?

Al

[heinz-oz]

Firstly I would like to disagree with vidoman, TV doesn't use ppi either, only scanners do

The reason why TV's don't use either dpi or ppi is simple, the TV frame size, depending on the type of TV and the TV standard is 720 x 480 (NTSC) or 720 x 576 (PAL/SECAM). These are usually considered 4:3 aspect ratio. 16:9 ratio TV's have a different frame size but can also be the same as for 4:3, confusing? I know.

Having said that, a TV picture is going to be that frame size, never mind if it is a 4" portable or 32" inch, flat screen or standard CRT.

The scanner uses ppi in order to determine the physical size of an image, i.e. 6 x 4" from a small slide or image. It will scan ( if it can) the right number of pixels per inch (ppi) along each side of the original image to ensure you have sufficient pixels available afterward to print your scanned image at a given resolution in dpi (dots per inch).

All this has absolutely no effect on an image displayed on a monitor or TV. It will display it's given frame size and the image will either be scaled to fit that frame or display smaller if it is smaller than the TV standards frame size.

There is absolutely no advantage in feeding images larger than the TV frame size into it, PS will have to scale this down by discarding pixels and "guessing" the best content for the pixels surrounding the dropped one.

I don't know PS all that well, have used it only once, but all the above applies to anything you can use to put pictures on a TV screen. I do my slide shows in MSP 8 or DVD MF 5+ and I use bmp images of the correct size. These look crisper to my eyes than when I use jpegs. I reckon this is due to the resizing I do prior. The images start out as digital images from a camera, in jpeg. If I modify these images which I do because I have to resize/crop them and then save them again as jpeg, the jpeg compression is applied again discarding even more detail.

Starting from a scanned image, I would scan to tiff at a suitable resolution to keep the resultant image frame size close to the target frame size. Then I would crop the image to the right aspect ratio/frame size and save as bmp or jpeg.

PS does not use a "native" resolution because it doesn't exist. It uses the frame size of the TV standard in your area or the one that is set in the project properties. Even though I live in PAL land, there is nothing stopping me from making an NTSC slide slow.

[sjj1805]

the TV frame size, depending on the type of TV and the TV standard is 720 x 480 (NTSC) or 720 x 576 (PAL/SECAM). These are usually considered 4:3 aspect ratio. 16:9 ratio TV's have a different frame size but can also be the same as for 4:3, confusing? I know.

To clarify this confusion which I always had trouble getting my head round until the penny dropped. Pixels are oblong in shape. Therefore you can have:
720 narrow oblongs x 576 rows = 4x3
720 wide oblongs x 576 rows = 16.9

[brennerpr]

This post basically answers my question in my separate post about resolution. But why would the picture show output, when I run it, look so lousy on my computer screen (and TV, when I burn a DVD)? The photos I'm uploading are very high quality.