# Q on graphic size

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Anonymous
June 3, 2005 11:12:58 PM

During this memorial holiday vacation, I took tons of pictures with a new
Sony DSC T1 digital camera (5MP).
In order to save space, image size was set at 3MP (instead of 5MP). Then,
images were downloaded to my computers. The images looked great to my
naked eyes. When I looked at the files, all of them are in jpg format but
the images sizes are 1.3MB to 1.4 MB. I expected them to be 5mb. I am
wondering what is the conversion equation from MP to MB. Please enlighten
me. TIA. Satoshi

Anonymous
June 4, 2005 12:45:36 AM

satoshi wrote:
> During this memorial holiday vacation, I took tons of pictures with a new
> Sony DSC T1 digital camera (5MP).
> In order to save space, image size was set at 3MP (instead of 5MP). Then,
> images were downloaded to my computers. The images looked great to my
> naked eyes. When I looked at the files, all of them are in jpg format but
> the images sizes are 1.3MB to 1.4 MB. I expected them to be 5mb. I am
> wondering what is the conversion equation from MP to MB. Please enlighten
> me. TIA. Satoshi

There is no conversion btwn MP & MB with jpegs. Jpeg file sizes can vary
depending on compression. Mexapixels (MP) is simply the number of pixels.
Anonymous
June 4, 2005 1:56:06 AM

"satoshi" <satoshi@thuntek.net> writes:

> During this memorial holiday vacation, I took tons of pictures with a new
> Sony DSC T1 digital camera (5MP).

> In order to save space, image size was set at 3MP (instead of 5MP).
> great to my naked eyes. When I looked at the files, all of them are
> in jpg format but the images sizes are 1.3MB to 1.4 MB. I expected
> them to be 5mb. I am wondering what is the conversion equation from
> MP to MB. Please enlighten me.

Pixels ain't bytes! That's why they have different names.

In most images you will work with, each pixel is represented by
*three* bytes, one giving the red light intensity, one giving the
green light intensity, and one giving the blue light intensity.
Uncompressed, a 3MP image would take up 3MB.

JPEG compression is really *very* good at making still image files
smaller. I guess those alleged "experts" really were! (JPEG stands
for "Joint Photographic Experts Group").

So that's how your 3MP images end up as 1.3MB or so files. The exact
degree of compression depends on the JPEG settings used (your camera
may well give you a couple of choices, often called things like
"normal", "fine", or "super-fine") AND on the content of the image
(hence the variation in size between images taken with the same
settings).

I have no idea how you managed to start out expecting the files to be
5MB for 3MP images, by the way; I don't follow that bit. Not
important, really.

(I'm talking here about "24-bit color", which is what the vast
majority of images floating around in the digital world are in I
think. I'm avoiding other, more complicated, cases because they don't
seem relevant to the original poster's question, not because I've
never heard of them.)
--
David Dyer-Bennet, <mailto d-b@dd-b.net>, <http://www.dd-b.net/dd-b/&gt;
RKBA: <http://noguns-nomoney.com/&gt; <http://www.dd-b.net/carry/&gt;
Pics: <http://dd-b.lighthunters.net/&gt; <http://www.dd-b.net/dd-b/SnapshotAlbum/&gt;
Dragaera/Steven Brust: <http://dragaera.info/&gt;
Related resources
Anonymous
June 4, 2005 2:35:46 AM

satoshi wrote:

Just to touch on David's excellent reply..

All your 3 megapixel images are 9 megabytes in size. They have
to be to hold the 3 color information David described.

With JPEG, the images are COMPRESSED before they are saved
to your memory card. JPEG uses a very efficient compression
algorithm which results in very small file sizes.

This scheme saves disk space and reduces transfer time over a
network, or between devices like your camera and computer.

When you open JPEG images and view them on your computer, they
must be uncompressed back to the required 9 megabytes by whatever
software you are using to view the image. They exist as 1.4MB
files on your hard disk, but get inflated back to 9 megabytes when
they are transferred to your computer memory.
Anonymous
June 4, 2005 3:00:33 AM

David Dyer-Bennet wrote:

> "satoshi" <satoshi@thuntek.net> writes:
>
>> I am wondering what is the conversion equation from
>> MP to MB. Please enlighten me.
>
>
> Pixels ain't bytes!

Thanks for that clear statement <g>.
Anonymous
June 4, 2005 3:43:28 AM

> satoshi wrote:
>
> Just to touch on David's excellent reply..
>
> All your 3 megapixel images are 9 megabytes in size. They have
> to be to hold the 3 color information David described.

I somehow typed the wrong number in my message. AAIIIIEEEEEE! I
remember so clearly thinking the right thing, and I never noticed
before sending it off. Anyone know a good shop to do a CLA on a
slightly used brain?
--
David Dyer-Bennet, <mailto d-b@dd-b.net>, <http://www.dd-b.net/dd-b/&gt;
RKBA: <http://noguns-nomoney.com/&gt; <http://www.dd-b.net/carry/&gt;
Pics: <http://dd-b.lighthunters.net/&gt; <http://www.dd-b.net/dd-b/SnapshotAlbum/&gt;
Dragaera/Steven Brust: <http://dragaera.info/&gt;
Anonymous
June 4, 2005 7:11:07 AM

satoshi wrote:
> During this memorial holiday vacation, I took tons of pictures with a new
> Sony DSC T1 digital camera (5MP).
> In order to save space, image size was set at 3MP (instead of 5MP). Then,
> images were downloaded to my computers. The images looked great to my
> naked eyes. When I looked at the files, all of them are in jpg format but
> the images sizes are 1.3MB to 1.4 MB. I expected them to be 5mb. I am
> wondering what is the conversion equation from MP to MB. Please enlighten
> me. TIA. Satoshi
>
>
The unprocessed size of a 3mp picture is 9 megabytes. Cameras that
output .jpg files always compress the data to save space on the flash
cards. The compression varies from picture to picture, but usually runs
somewhere close to 10:1, so your pictures are well within the range of
most cameras as to compression.

The camera captures 24 bits (3 bytes) of data for each pixel, so
multiply the 'mp' size by 3 for the 'raw' size of the image. Then .jpg
compression is applied to the data.

--
Ron Hunter rphunter@charter.net
Anonymous
June 4, 2005 7:12:28 AM

David Dyer-Bennet wrote:
> "satoshi" <satoshi@thuntek.net> writes:
>
>
>>During this memorial holiday vacation, I took tons of pictures with a new
>>Sony DSC T1 digital camera (5MP).
>
>
>>In order to save space, image size was set at 3MP (instead of 5MP).
>>great to my naked eyes. When I looked at the files, all of them are
>>in jpg format but the images sizes are 1.3MB to 1.4 MB. I expected
>>them to be 5mb. I am wondering what is the conversion equation from
>>MP to MB. Please enlighten me.
>
>
> Pixels ain't bytes! That's why they have different names.
>
> In most images you will work with, each pixel is represented by
> *three* bytes, one giving the red light intensity, one giving the
> green light intensity, and one giving the blue light intensity.
> Uncompressed, a 3MP image would take up 3MB.

No. 9MB!

>
> JPEG compression is really *very* good at making still image files
> smaller. I guess those alleged "experts" really were! (JPEG stands
> for "Joint Photographic Experts Group").
>
> So that's how your 3MP images end up as 1.3MB or so files. The exact
> degree of compression depends on the JPEG settings used (your camera
> may well give you a couple of choices, often called things like
> "normal", "fine", or "super-fine") AND on the content of the image
> (hence the variation in size between images taken with the same
> settings).
>
> I have no idea how you managed to start out expecting the files to be
> 5MB for 3MP images, by the way; I don't follow that bit. Not
> important, really.
>
> (I'm talking here about "24-bit color", which is what the vast
> majority of images floating around in the digital world are in I
> think. I'm avoiding other, more complicated, cases because they don't
> seem relevant to the original poster's question, not because I've
> never heard of them.)

--
Ron Hunter rphunter@charter.net
Anonymous
June 4, 2005 7:14:49 AM

David Dyer-Bennet wrote:
>
>
>>satoshi wrote:
>>
>>Just to touch on David's excellent reply..
>>
>>All your 3 megapixel images are 9 megabytes in size. They have
>>to be to hold the 3 color information David described.
>
>
> I somehow typed the wrong number in my message. AAIIIIEEEEEE! I
> remember so clearly thinking the right thing, and I never noticed
> before sending it off. Anyone know a good shop to do a CLA on a
> slightly used brain?

Slightly used? Sigh. At my age, 'slightly' isn't the accurate term. I
was sure, given the accuracy of the rest of your response that you
were suffering from a common newsgroup problem, fast brain, slow
fingers.... Grin.

--
Ron Hunter rphunter@charter.net
Anonymous
June 4, 2005 7:19:52 AM

satoshi wrote:

> During this memorial holiday vacation, I took tons of pictures with a new
> Sony DSC T1 digital camera (5MP).
> In order to save space, image size was set at 3MP (instead of 5MP). Then,
> images were downloaded to my computers. The images looked great to my
> naked eyes. When I looked at the files, all of them are in jpg format but
> the images sizes are 1.3MB to 1.4 MB. I expected them to be 5mb. I am
> wondering what is the conversion equation from MP to MB. Please enlighten
> me. TIA. Satoshi
>
>
Hi,
Are you trolling? I am serious!
Pixel and bytes are two different thing.
Tony
Anonymous
June 4, 2005 11:21:30 AM

Thanks for excellent posts from you and others.

>I have no idea how you managed to start out expecting the files to be
>5MB for 3MP

5MB was a typo. In fact, I was not thinking 3b for 1 px for color.
Sometime, brain cells do not work properly.

Thanks again. Satoshi

"David Dyer-Bennet" <dd-b@dd-b.net> wrote in message
news:m2slzybzjt.fsf@gw.dd-b.net...
> "satoshi" <satoshi@thuntek.net> writes:
>
>> During this memorial holiday vacation, I took tons of pictures with a new
>> Sony DSC T1 digital camera (5MP).
>
>> In order to save space, image size was set at 3MP (instead of 5MP).
>> great to my naked eyes. When I looked at the files, all of them are
>> in jpg format but the images sizes are 1.3MB to 1.4 MB. I expected
>> them to be 5mb. I am wondering what is the conversion equation from
>> MP to MB. Please enlighten me.
>
> Pixels ain't bytes! That's why they have different names.
>
> In most images you will work with, each pixel is represented by
> *three* bytes, one giving the red light intensity, one giving the
> green light intensity, and one giving the blue light intensity.
> Uncompressed, a 3MP image would take up 3MB.
>
> JPEG compression is really *very* good at making still image files
> smaller. I guess those alleged "experts" really were! (JPEG stands
> for "Joint Photographic Experts Group").
>
> So that's how your 3MP images end up as 1.3MB or so files. The exact
> degree of compression depends on the JPEG settings used (your camera
> may well give you a couple of choices, often called things like
> "normal", "fine", or "super-fine") AND on the content of the image
> (hence the variation in size between images taken with the same
> settings).
>
> I have no idea how you managed to start out expecting the files to be
> 5MB for 3MP images, by the way; I don't follow that bit. Not
> important, really.
>
> (I'm talking here about "24-bit color", which is what the vast
> majority of images floating around in the digital world are in I
> think. I'm avoiding other, more complicated, cases because they don't
> seem relevant to the original poster's question, not because I've
> never heard of them.)
> --
> David Dyer-Bennet, <mailto d-b@dd-b.net>, <http://www.dd-b.net/dd-b/&gt;
> RKBA: <http://noguns-nomoney.com/&gt; <http://www.dd-b.net/carry/&gt;
> Pics: <http://dd-b.lighthunters.net/&gt;
> <http://www.dd-b.net/dd-b/SnapshotAlbum/&gt;
> Dragaera/Steven Brust: <http://dragaera.info/&gt;
Anonymous
June 4, 2005 3:42:21 PM

"satoshi" <satoshi@thuntek.net> writes:

> Thanks for excellent posts from you and others.
>
>>I have no idea how you managed to start out expecting the files to be
>>5MB for 3MP
>
> 5MB was a typo. In fact, I was not thinking 3b for 1 px for color.
> Sometime, brain cells do not work properly.

Tell me about it; you've seen by now that *I* managed to mess up the
size numbers while correcting you on them!
--
David Dyer-Bennet, <mailto d-b@dd-b.net>, <http://www.dd-b.net/dd-b/&gt;
RKBA: <http://noguns-nomoney.com/&gt; <http://www.dd-b.net/carry/&gt;
Pics: <http://dd-b.lighthunters.net/&gt; <http://www.dd-b.net/dd-b/SnapshotAlbum/&gt;
Dragaera/Steven Brust: <http://dragaera.info/&gt;
Anonymous
June 4, 2005 9:15:13 PM

David,

In comparison to conventional film cameras, I feel the steep learning curve
for beginners using digital cameras. I still could not digest the whole
manual. RAM in my head was not big enough to hold all howtos. I wish that
I could implant a 1GB RAM to my brain. Pictures were taken with Sony T1
(5MP) in Sedona, Arizona during the past memorial holiday. That was my
first exposure to digital camera. In order to save memory space in memory
stick, I set the picture size to 3mp. When downloaded, all of them were in
1.1-1.3 MB size. I was worried about the quality of prints. That worry
triggered me to post the question to this NG.

Pictures were printed at Costco at a cost of 17c/print (3 x 5). All
pictures were turned out to be sharp and gorgeous. To my naked eyes, I do
not see any difference between digital and film prints. I am now a
satisfied customer with Sony Camera. Good bye to my Pentax and Olympus
film cameras. Satoshi

"David Dyer-Bennet" <dd-b@dd-b.net> wrote in message
news:m2zmu6m5ua.fsf@gw.dd-b.net...
> "satoshi" <satoshi@thuntek.net> writes:
>
>> Thanks for excellent posts from you and others.
>>
>>>I have no idea how you managed to start out expecting the files to be
>>>5MB for 3MP
>>
>> 5MB was a typo. In fact, I was not thinking 3b for 1 px for color.
>> Sometime, brain cells do not work properly.
>
> Tell me about it; you've seen by now that *I* managed to mess up the
> size numbers while correcting you on them!
> --
> David Dyer-Bennet, <mailto d-b@dd-b.net>, <http://www.dd-b.net/dd-b/&gt;
> RKBA: <http://noguns-nomoney.com/&gt; <http://www.dd-b.net/carry/&gt;
> Pics: <http://dd-b.lighthunters.net/&gt;
> <http://www.dd-b.net/dd-b/SnapshotAlbum/&gt;
> Dragaera/Steven Brust: <http://dragaera.info/&gt;
Anonymous
June 4, 2005 11:44:42 PM

"satoshi" <satoshi@thuntek.net> writes:

> In comparison to conventional film cameras, I feel the steep
> learning curve for beginners using digital cameras.

I can easily believe it. I came to digital photography only after 30
years of film photography (including medium and large format as well
as 35mm, and doing my own darkroom work a lot) and 30 years of
computer programming; and before I started actual digital
*photography*, I'd been working with scanned images (and later
scanning my own film) for 5 or so years. I had a big head start on
the learning curve, and I took it really slow. And I'm sure there are
a number of features of my current camera I'm still not using
optimally!

> I still could not digest the whole manual. RAM in my head was not
> big enough to hold all howtos. I wish that I could implant a 1GB
> RAM to my brain. Pictures were taken with Sony T1 (5MP) in Sedona,
> Arizona during the past memorial holiday. That was my first
> exposure to digital camera. In order to save memory space in memory
> stick, I set the picture size to 3mp. When downloaded, all of them
> were in 1.1-1.3 MB size. I was worried about the quality of prints.
> That worry triggered me to post the question to this NG.

I hope I didn't give the impression I thought you were "dumb". A bit
confused, yes, but then you already knew that, it's what prompted you
to ask the question in the first place. Ignorance is curable, and

> Pictures were printed at Costco at a cost of 17c/print (3 x 5). All
> pictures were turned out to be sharp and gorgeous. To my naked eyes, I do
> not see any difference between digital and film prints. I am now a
> satisfied customer with Sony Camera. Good bye to my Pentax and Olympus
> film cameras. Satoshi

Good, glad that worked out. It *should* have worked out, 3MP is fine
for that small print size. It's nice when practice works as predicted
in theory!
--
David Dyer-Bennet, <mailto d-b@dd-b.net>, <http://www.dd-b.net/dd-b/&gt;
RKBA: <http://noguns-nomoney.com/&gt; <http://www.dd-b.net/carry/&gt;
Pics: <http://dd-b.lighthunters.net/&gt; <http://www.dd-b.net/dd-b/SnapshotAlbum/&gt;
Dragaera/Steven Brust: <http://dragaera.info/&gt;
Anonymous
June 4, 2005 11:44:43 PM

In fact, I was pleasantry surprised to see such nice prints. I could not
believe those prints. I read tons of comments saying that digital prints
won't match film prints. That's what I was concerned. For amateurs, they
won't likely for 8 x 10 prints unless those have to do with very important
events. This first exposure of digital camera tells me that 3-5 mp camera
would make everybody happy. I just learned that New Canon Eos 20Da will
have "LCD preview" :
http://www.steves-digicams.com/pr/canon_06022005_20da_p.... I might
consider to upgrade to this dSLR by the end of this year. Thanks for the
wonderful and practical information on digital image from this NG. I thank
to David for your kind understanding. Satoshi

"David Dyer-Bennet" <dd-b@dd-b.net> wrote in message
news:m23brxd43p.fsf@gw.dd-b.net...
> "satoshi" <satoshi@thuntek.net> writes:
>
>> In comparison to conventional film cameras, I feel the steep
>> learning curve for beginners using digital cameras.
>
> I can easily believe it. I came to digital photography only after 30
> years of film photography (including medium and large format as well
> as 35mm, and doing my own darkroom work a lot) and 30 years of
> computer programming; and before I started actual digital
> *photography*, I'd been working with scanned images (and later
> scanning my own film) for 5 or so years. I had a big head start on
> the learning curve, and I took it really slow. And I'm sure there are
> a number of features of my current camera I'm still not using
> optimally!
>
>> I still could not digest the whole manual. RAM in my head was not
>> big enough to hold all howtos. I wish that I could implant a 1GB
>> RAM to my brain. Pictures were taken with Sony T1 (5MP) in Sedona,
>> Arizona during the past memorial holiday. That was my first
>> exposure to digital camera. In order to save memory space in memory
>> stick, I set the picture size to 3mp. When downloaded, all of them
>> were in 1.1-1.3 MB size. I was worried about the quality of prints.
>> That worry triggered me to post the question to this NG.
>
> I hope I didn't give the impression I thought you were "dumb". A bit
> confused, yes, but then you already knew that, it's what prompted you
> to ask the question in the first place. Ignorance is curable, and
> there's nothing shameful about it.
>
>> Pictures were printed at Costco at a cost of 17c/print (3 x 5). All
>> pictures were turned out to be sharp and gorgeous. To my naked eyes, I
>> do
>> not see any difference between digital and film prints. I am now a
>> satisfied customer with Sony Camera. Good bye to my Pentax and Olympus
>> film cameras. Satoshi
>
> Good, glad that worked out. It *should* have worked out, 3MP is fine
> for that small print size. It's nice when practice works as predicted
> in theory!
> --
> David Dyer-Bennet, <mailto d-b@dd-b.net>, <http://www.dd-b.net/dd-b/&gt;
> RKBA: <http://noguns-nomoney.com/&gt; <http://www.dd-b.net/carry/&gt;
> Pics: <http://dd-b.lighthunters.net/&gt;
> <http://www.dd-b.net/dd-b/SnapshotAlbum/&gt;
> Dragaera/Steven Brust: <http://dragaera.info/&gt;
Anonymous
June 5, 2005 7:49:40 AM

satoshi <satoshi@thuntek.net> wrote:
: In fact, I was pleasantry surprised to see such nice prints. I could
: not believe those prints. I read tons of comments saying that digital
: prints won't match film prints. That's what I was concerned. For
: amateurs, they won't likely for 8 x 10 prints unless those have to do
: with very important events. This first exposure of digital camera
: tells me that 3-5 mp camera would make everybody happy.

a 3mp image should be able to be printed up to 8x10 with acceptable
results. If you are primarily interrested in 3x5s your 3mp images should
be great. And you will even have a little "breathing room" if you decide
to crop the image a bit. If you think that you may want to crop and then
print to 8x10 you may want to bump the camera back up to 5mp so you keep
that breathing room.

Randy

==========
Randy Berbaum
Champaign, IL
Anonymous
June 5, 2005 11:44:18 AM

Randy, I reset the camera to 5mp size.
I now have 500 mb memory stick.

Let me ask you this question: What format does Costco or other companies
(e.g., ofoto) accept for printing?
What I meant was whether they take cdr, tiff, pdf (converted to pdf with
Photoshop), psd (photoshop format) or other formats to print. If they
could take pdf, it would be great. Satoshi

"Randy Berbaum" <rberbaum@bluestem.prairienet.org> wrote in message
news 7tsok\$ava\$1@wildfire.prairienet.org...
> satoshi <satoshi@thuntek.net> wrote:
> : In fact, I was pleasantry surprised to see such nice prints. I could
> : not believe those prints. I read tons of comments saying that digital
> : prints won't match film prints. That's what I was concerned. For
> : amateurs, they won't likely for 8 x 10 prints unless those have to do
> : with very important events. This first exposure of digital camera
> : tells me that 3-5 mp camera would make everybody happy.
>
> a 3mp image should be able to be printed up to 8x10 with acceptable
> results. If you are primarily interrested in 3x5s your 3mp images should
> be great. And you will even have a little "breathing room" if you decide
> to crop the image a bit. If you think that you may want to crop and then
> print to 8x10 you may want to bump the camera back up to 5mp so you keep
> that breathing room.
>
> Randy
>
> ==========
> Randy Berbaum
> Champaign, IL
>
Anonymous
June 6, 2005 8:22:52 AM

satoshi <satoshi@thuntek.net> wrote:
: Randy, I reset the camera to 5mp size.
: I now have 500 mb memory stick.

: Let me ask you this question: What format does Costco or other companies
: (e.g., ofoto) accept for printing?
: What I meant was whether they take cdr, tiff, pdf (converted to pdf with
: Photoshop), psd (photoshop format) or other formats to print. If they
: could take pdf, it would be great. Satoshi

Since I have never used any of these locations I don't know the price they
charge. I do all my own printing at home. But from what I have taken from
similar discussions I think most places prefer JPG files but some
locations use machinery that can take other file formats. Your best bet
would be to phone your local store and ask the folks at the photography
desk what formats their equipment can handle. It is possible that some of
them may be able to use a Photoshop format, but this would probably be
fewer than other more prevalent formats (Adobe tends to be protective of
their in-house formats). But if you convert one of these files to a low
compression (12) JPG just for transport to the photo shop for printing you
should do just fine. Remember that if you have multiple layers on a PS
formated photo, you will have to "flatten" it before you can "save as" a
JPG file.

Randy

==========
Randy Berbaum
Champaign, IL
June 6, 2005 5:20:48 PM

satoshi wrote:
> During this memorial holiday vacation, I took tons of pictures with a new
> Sony DSC T1 digital camera (5MP).
> In order to save space, image size was set at 3MP (instead of 5MP). Then,
> images were downloaded to my computers. The images looked great to my
> naked eyes. When I looked at the files, all of them are in jpg format but
> the images sizes are 1.3MB to 1.4 MB. I expected them to be 5mb. I am
> wondering what is the conversion equation from MP to MB. Please enlighten
> me. TIA. Satoshi
>
>
The size of a .jpg file depends on the compression factor, and on details of the picture.
I set the compression factor for my 3 Mp camera by experimenting with the
compressions available, and I settled on one that gives files of about 2/3 Mp. You
either have a minimal compression factor, or your photos may be 5 Mp. Perhaps your camera
didn't maintain the 3 Mp setting you made.
Anonymous
June 8, 2005 12:01:27 AM

On Fri, 03 Jun 2005 21:56:06 -0500, David Dyer-Bennet <dd-b@dd-b.net>
wrote:

>"satoshi" <satoshi@thuntek.net> writes:
>
>> During this memorial holiday vacation, I took tons of pictures with a new
>> Sony DSC T1 digital camera (5MP).
>
>> In order to save space, image size was set at 3MP (instead of 5MP).
>> great to my naked eyes. When I looked at the files, all of them are
>> in jpg format but the images sizes are 1.3MB to 1.4 MB. I expected
>> them to be 5mb. I am wondering what is the conversion equation from
>> MP to MB. Please enlighten me.
>
>Pixels ain't bytes! That's why they have different names.
>
>In most images you will work with, each pixel is represented by
>*three* bytes, one giving the red light intensity, one giving the
>green light intensity, and one giving the blue light intensity.
>Uncompressed, a 3MP image would take up 3MB.
>
>JPEG compression is really *very* good at making still image files
>smaller. I guess those alleged "experts" really were! (JPEG stands
>for "Joint Photographic Experts Group").
>
>So that's how your 3MP images end up as 1.3MB or so files. The exact
>degree of compression depends on the JPEG settings used (your camera
>may well give you a couple of choices, often called things like
>"normal", "fine", or "super-fine") AND on the content of the image
>(hence the variation in size between images taken with the same
>settings).
>
>I have no idea how you managed to start out expecting the files to be
>5MB for 3MP images, by the way; I don't follow that bit. Not
>important, really.

Maybe because of the logic implied in your statement above,
"In most images you will work with, each pixel is represented by
*three* bytes, one giving the red light intensity, one giving the
green light intensity, and one giving the blue light intensity", which
would get you to 9MB for openers, not, as you further said,
"Uncompressed, a 3MP image would take up 3MB."

>
>(I'm talking here about "24-bit color", which is what the vast
>majority of images floating around in the digital world are in I
>think. I'm avoiding other, more complicated, cases because they don't
>seem relevant to the original poster's question, not because I've
>never heard of them.)
!