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Square pixels & Dual use Digital Camera

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September 15, 2005 1:55:24 PM

Archived from groups: rec.photo.digital (More info?)

Hi -

I've noticed that most if not all images taken by digital cameras (at
least the ones I've used) appear 'squashed' differently in landscape
and in portrait. Why is this so? (I'm thinking of buying a digital
camera soon and I dont want one that behaves like this.)

Also, I've heard someone say in the past that some digital camaras can
double as webcams. Can anyone recommend one that has this dual use?

Thanks,

- Olumide
Anonymous
September 15, 2005 4:05:07 PM

Archived from groups: rec.photo.digital (More info?)

50295@web.de wrote:
> Hi -
>
> I've noticed that most if not all images taken by digital cameras (at
> least the ones I've used) appear 'squashed' differently in landscape
> and in portrait. Why is this so? (I'm thinking of buying a digital
> camera soon and I dont want one that behaves like this.)
>
> Also, I've heard someone say in the past that some digital camaras can
> double as webcams. Can anyone recommend one that has this dual use?
>
> Thanks,
>
> - Olumide
>
I have NEVER observed this effect on any of my 4 digicams, nor have I
heard anyone else raise the question.
I suspect that your monitor needs adjusting.
Try printing an image. Is it still squashed?
Bob Williams
Anonymous
September 15, 2005 5:46:34 PM

Archived from groups: rec.photo.digital (More info?)

<50295@web.de> wrote in message
news:1126803324.192755.6240@f14g2000cwb.googlegroups.com...
> Hi -
>
> I've noticed that most if not all images taken by digital cameras (at
> least the ones I've used) appear 'squashed' differently in landscape
> and in portrait. Why is this so? (I'm thinking of buying a digital
> camera soon and I dont want one that behaves like this.)
>
> Also, I've heard someone say in the past that some digital camaras can
> double as webcams. Can anyone recommend one that has this dual use?
>
> Thanks,
>
> - Olumide
>
I've never seen this and I've been exposed to numerous digicams over the
years. One of Nikon's older dSLRs had pixels (actually sensor wells on the
chip) that were taller than wide, but the output was sampled so the vertical
and horzontal scaled the same with the subject photographed. The effect was
slight loss in vertical resolution. Glad this "cheat" was canned in later
models.

If you use a CRT, and the raster height and size are not set for the 4:3
size ratio of the width to height, things could look stretched/squashed.
-S
Related resources
Anonymous
September 15, 2005 10:33:27 PM

Archived from groups: rec.photo.digital (More info?)

50295@web.de wrote:
> Hi -
>
> I've noticed that most if not all images taken by digital cameras (at
> least the ones I've used) appear 'squashed' differently in landscape
> and in portrait. Why is this so? (I'm thinking of buying a digital
> camera soon and I dont want one that behaves like this.)

Most likely the pictures were displayed incorrectly. The great majority
of still cameras use square pixels.

David
Anonymous
September 16, 2005 6:28:51 AM

Archived from groups: rec.photo.digital (More info?)

"David J Taylor" <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk.invalid> writes:

>Most likely the pictures were displayed incorrectly. The great majority
>of still cameras use square pixels.

And even when the pixels on the sensor are not arranged in a square grid
(e.g. some Nikon DSLRs), the data is resampled so the pixels in the
output file are square.

Software that can handle non-square pixels well is mostly limited to the
video world, where non-square pixels are common.

Dave
Anonymous
September 16, 2005 7:40:54 PM

Archived from groups: rec.photo.digital (More info?)

"Bob Williams" <mytbobnospam@cox.net> wrote in message
news:SBjWe.253182$E95.46477@fed1read01...
>
>
> 50295@web.de wrote:
>> Hi -
>>
>> I've noticed that most if not all images taken by digital cameras (at
>> least the ones I've used) appear 'squashed' differently in landscape
>> and in portrait. Why is this so? (I'm thinking of buying a digital
>> camera soon and I dont want one that behaves like this.)
>>
>> Also, I've heard someone say in the past that some digital camaras can
>> double as webcams. Can anyone recommend one that has this dual use?
>>
>> Thanks,
>>
>> - Olumide
>>
> I have NEVER observed this effect on any of my 4 digicams, nor have I
> heard anyone else raise the question.
> I suspect that your monitor needs adjusting.
> Try printing an image. Is it still squashed?
> Bob Williams

I too have never observed this on a monitor. However, and I've posted this
before, when I copied my canon A40 pictures to cd and play them in my dvd
player, I get vertical elongation. I don't see this if I use the video
output of the camera, neither do I see it if I make a slide show using MyDVD
slide show software. It get's fixed if I resample to 640x 420. Note the
aspect ratio for tv is 4:3, same the 1600x1200 pixel size of images. I'm
wondering if this has something to do with the dvd player. It does have a
setting to switch between letterbox and tv which doesn't ever seem to do
anything.
Dave Cohen
Anonymous
September 17, 2005 7:43:15 AM

Archived from groups: rec.photo.digital (More info?)

Dave Cohen wrote:

> However, and I've posted this before, when I copied my canon A40
> pictures to cd and play them in my dvd player, I get vertical
> elongation. I don't see this if I use the video output of the camera,
> neither do I see it if I make a slide show using MyDVD slide show
> software. It get's fixed if I resample to 640x 420.
> Note the aspect ratio for tv is 4:3, same the 1600x1200 pixel size of
> images. I'm wondering if this has something to do with
> the dvd player. It does have a setting to switch between
> letterbox and tv which doesn't ever seem to do anything.

Computers and digital still cameras are - generally speaking and not
accounting for the RAW formats - using so-called "square pixels": the
height of each pixel is considered the same as its width. In other
words, the pixels form an evenly spaced sampling grid in both vertical
and horizontal directions, and the spacing is the same in both
directions.

DVD players - and DV camcorders, for that matter - do not work this way.
Instead, they are using so-called "ITU-R BT.601" [1] pixels (or, in some
cases, derivatives of thereof). The pixels are not square in shape, but
rectangular - in other words, the width occupied by an individual pixel
is not the same as its height. Not only that, but there's another
complication as well: the size of the sampling matrix is not exactly
"4:3" or "16:9", either - even if we're taking the rectangular shape of
the pixels in account.

To put this information in practical numbers, the nominal "PAL"
(625-line / 50 Hz tv systems) resolution for 4:3 DVD stills is 720×576.
However, only the centermost 702×576 pixels actually belong to the "4:3"
area - there are 9 pixels "extra" on both sides. Therefore, if you want
to create a full screen DVD video image for this target resolution from
a square-pixel source, while retaining the correct aspect ratio, you
will need to edit your images in 788×576 (square pixels), and then
downsample - only in the horizontal direction - to 720×576, which will
give you DVD pixels in their correct shape.

For "NTSC" (525-line / 59.97 Hz tv systems), it is basically the same,
but the values are a little bit different. The nominal "NTSC" DVD 4:3
resolution is 720×480, but once again, the pixels are not square, and
the shape of the spatial area that this sampling matrix represents -
even if we're taking the rectangluar shape of the pixels in account - is
not exactly "4:3". Long story short, in this case, you would want to
edit your original image using the resolution of 720×527 (square
pixels), and then resample (only in the vertical direction!) to 720×480
("NTSC" DVD pixels.)

Note that some entry-level DVD authoring apps may insist on resampling
from "square pixels" to "DVD pixels" automatically - making it
impossible for the user to do these conversions in advance. (Sadly, it
is also often the case that the programmers of these apps are not
necessarily always even using the right numbers for these conversions,
so the aspect ratio may be a little bit off.) If your authoring
application lets you import images which are already preconverted to DV
pixels without resampling/scaling them further, you will be fine by
using the above-mentioned numbers. If, however, your wants to make all
scaling on its own, you will need to figure out what it is actually
doing in order to fix the problem.

Also note that all domestic tv sets overscan, i.e. they don't show the
image up to the very edges. Video industry has the concept of "safe
area" - this is a smaller rectangle inside a full screen image; an area
which is usually "guaranteed" to show up on most of the tv screens, and
which is used as a guide for aligning captions, titles and graphics so
that they will not get off-screen on domestic sets. When making albums
of digital photographs in the DVD format, overscan needs to be taken
into account, too - especially if you have pictures that have important
details on the very edges.

If you'd like to delve further into these topics, check out these sites:

<http://www.iki.fi/znark/video/conversion/&gt;
<http://scanline.ca/overscan/&gt;

Good information can also be found on the rec.video.desktop newsgroup:

<news:rec.video.desktop>

_____

[1] ITU, or International Telecommunication Union, is an international
standards organization that has published many standards in the fields
of telecommunications and broadcast industry (including both radio &
tv.) ITU-R BT.601 is one of the standards published by this body, and it
defines the characteristics of digitized SD resolution video as used in
professional broadcast applications. (Domestic digital video equipment -
such as DV or DVD - is based on this standard as well, as far as the
shape of the pixels goes.)

--
znark
Anonymous
September 17, 2005 8:40:14 AM

Archived from groups: rec.photo.digital (More info?)

<50295@web.de> wrote:
>I've noticed that most if not all images taken by digital cameras (at
>least the ones I've used) appear 'squashed' differently in landscape
>and in portrait. Why is this so? (I'm thinking of buying a digital
>camera soon and I dont want one that behaves like this.)

Your monitor needs adjusting.

>Also, I've heard someone say in the past that some digital camaras can
>double as webcams. Can anyone recommend one that has this dual use?

Expensive webcam. You'd do better to find a cheap camera designed for
the purpose.

--
Ray Fischer
rfischer@sonic.net
!