Need Simple Explanation of Camera 'Megapixels'

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geezer - 16 Mar 2005 15:38 GMT

I have a Toshiba PDR-3300 so-called 3.2 megapixel camera.

As a novice, I don't really understand what '3.2 megapixel' means.
Further I don't understand what 'resolution' I can expect from
resulting photos I take in terms of the jpeg images I end up with when
I upload the photos to my PC (WXP).

I am trying to learn the ins and outs of a photo editor, and it (and
others) say to always go for the 'highest resolution', when scanning
or using a camera. So that is what I feel I should to do, at least
within livable file size limits. But I can't seem to determine how my
camera-choices in this area affect resolution on my PC. I'm probably
just dumb here, but I would like some simple advice.

My camera has un-informing levels of 'size' (three) and 'quality'
(three). Of course the choices affect camera memory capacity and PC
file sizes. But I think I ALWAYS end up with PC resolution of 72ppi.

I eagerly await some help.

Thanks

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Doug Mitton - 16 Mar 2005 19:16 GMT

>I have a Toshiba PDR-3300 so-called 3.2 megapixel camera.
>
[quoted text clipped - 17 lines]
>
>Thanks

Here are a couple of links I came up with at random ... if you have
other questions after this come on back with specifics:

http://www.luminous-landscape.com/essays/

in particular

http://www.luminous-landscape.com/tutorials/understanding-series/res-demyst.shtml

is sort of an overview and the 2 links at the bottom provide support.

Also,
http://www.luminous-landscape.com/tutorials/understanding-series/index.shtml
has some good links!

Good luck!
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geezer - 16 Mar 2005 21:08 GMT

>Here are a couple of links I came up with at random ... if you have
>other questions after this come on back with specifics:
[quoted text clipped - 12 lines]
>
>Good luck!

I scanned the pages - at this point my first reaction is 'whew'!

Thanks

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Doug Mitton - 16 Mar 2005 23:37 GMT

>>Here are a couple of links I came up with at random ... if you have
>>other questions after this come on back with specifics:
[quoted text clipped - 16 lines]
>
>Thanks

Thats nothing! I'm on the http://www.pbase.com/canon_300d/ forum
(http://yahoogroups.com/group/Canon-300D/) and these types of links
fly in like machine-gun bullets. Some of them don't even have
registered domain names and are just IP addresses. It is very mind
boggling! :-)
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CSM1 - 16 Mar 2005 19:41 GMT

>I have a Toshiba PDR-3300 so-called 3.2 megapixel camera.

Review of the Toshiba PDR-3300.
http://www.dcresource.com/reviews/toshiba/pdr_3300-review/

> As a novice, I don't really understand what '3.2 megapixel' means.
> Further I don't understand what 'resolution' I can expect from
> resulting photos I take in terms of the jpeg images I end up with when
> I upload the photos to my PC (WXP).

Megapixels is simply the horizontal dimension multiplied by the vertical
dimension in pixels.
In your case the maximum size image is 2048 X 1536 (resolution), thus a
3,145,728 pixel image rounded to 3.2 Megapixel. Mega means million.

> I am trying to learn the ins and outs of a photo editor, and it (and
> others) say to always go for the 'highest resolution', when scanning
[quoted text clipped - 6 lines]
> (three). Of course the choices affect camera memory capacity and PC
> file sizes. But I think I ALWAYS end up with PC resolution of 72ppi.

If you read the review (and your manual), you will see that Size Full= 2048
X 1536 pixels, Size Half=1024 X 768 pixels and Size Small=640 X 480 pixels.

Quality is the amount of compression applied to the image in the camera. The
higher the quality (less compression) the larger the file size will be.

The 72 ppi is a arbitrary value that is picked because images do not have
DPI or PPI until printed. The size the image appears on your monitor is
dependant on the resolution of your monitor.

DPI or PPI can be changed to whatever you want it to be in a photo editor or
print dialog when printing the image. When printing you want the most pixels
in the image and a higher DPI. Best prints are printed at around 300 DPI.
For your 2048 x 1536 pixel image, you can get 6.8 inches x 5.12 inches when
printed at 300 DPI.

> I eagerly await some help.
>
> Thanks

Signature

CSM1
http://www.carlmcmillan.com
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geezer - 16 Mar 2005 20:57 GMT

>If you read the review (and your manual), you will see that Size Full= 2048
>X 1536 pixels, Size Half=1024 X 768 pixels and Size Small=640 X 480 pixels.

Yes - I read that.

>Quality is the amount of compression applied to the image in the camera. The
>higher the quality (less compression) the larger the file size will be.

Then why does the camera have 3 'size' settings and 3 'quality'
settings? That should give nine combos.

>The 72 ppi is a arbitrary value that is picked because images do not have
>DPI or PPI until printed. The size the image appears on your monitor is
>dependant on the resolution of your monitor.

I never thought of that. Mine is 72 ppi. But how do you explain that
when I scanned a 8X11 image in my HP950 MF printer/scanner, and I set
the 'scan settings' to an absurd 1200 for everything, when I brought
the resulting picture into the same editor it shows it as 1200 ppi
(before I touch it at all in the editor)? I am totally confused
there.

>DPI or PPI can be changed to whatever you want it to be in a photo editor or
>print dialog when printing the image. When printing you want the most pixels
[quoted text clipped - 5 lines]
>>
>> Thanks

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CSM1 - 16 Mar 2005 22:12 GMT

> >If you read the review (and your manual), you will see that Size Full= 2048
> >X 1536 pixels, Size Half=1024 X 768 pixels and Size Small=640 X 480 pixels.
[quoted text clipped - 17 lines]
> (before I touch it at all in the editor)? I am totally confused
> there.

Scanner software often puts the scan dpi in the jpg file. If does not for
every file format because not all image files store the dpi in the file. It
is necessary information to know when printing a scanned image at actual
size.

Your digital camera puts the 72 ppi in the jpg file because the manufacturer
chose to set the ppi at 72. Digital cameras do not create images with inches
or Centimeters.
All images created by digital cameras are pixels only. Unlike film which has
a dimension based on the width of the film base.

> >DPI or PPI can be changed to whatever you want it to be in a photo editor or
> >print dialog when printing the image. When printing you want the most pixels
[quoted text clipped - 6 lines]
> >> Thanks
>

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CSM1
http://www.carlmcmillan.com
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chrlz@go.com - 17 Mar 2005 00:38 GMT

Go to www.scantips.com and spend some quality time there! Try to keep
this in mind... All things being equal, the more pixels you have in
your image, the larger you can display/print it.

Those ppi and dpi figures are simply ratios that tell you how many of
those pixels are to be displayed per inch. In other words, let's say
your image file has 2000 pixels horizontally.. If you print it 10"
wide, then the 'resolution' will be 200 pixels per inch (which is
pretty good quality). If you print the same file to 20", it will be
100 pixels per inch (not so good, and you will start to see
pixellation), or to 5" wide it will be 400 ppi (extremely good quality)
and so on. Every image file has a ppi ratio `attached` to it (it is
just an information field in the file), but it doesn't affect the
actual number of pixels in the file, it is merely intended to be used
as a default quality for displaying or printing. There is nothing to
stop you printing the file at a different ppi, but you will always be
*quality* constrained by the number of pixels you actually have..

Screens tend to display images at around 80-100 dpi, so if you are
viewing that same 2000-pixel-wide image on screen (without zooming it),
it will appear to be a bit over 20" wide, and of course you will have
to scroll back and forth to be able to see the whole thing.

Keep thinking about it, and it will eventually click.

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