Megapixels and image size

Mogweed wrote:

 > I've not yet got a digital camera but I'm being drawn to the Pentax
 > Optio S.
 >
 > I'm not a photographer by any means and phrases like "f-stops", "white
 > balance", "histograms" and such like just leave me cold and mean
 > nothing whatsoever to me - and, I have to admit, I have no particular
 > interest in doing anything to change that situation. I'm strictly a
 > 'point-n-shoot' sort of guy which is why the Pentax appeals to me -
 > small enough to take anywhere and as long as it takes the holiday
 > snaps (both landscape scenery and inside the bars), that's all I want.
 >
 > The thing I need help with is understanding megapixels and print
 > sizes. I know that the Optio S is a 3.2 Mp camera and that that
 > equates to a resolution of 2048 x 1536 and I also know that that will
 > give a good quality print size of 8" x 10" but I've never needed or
 > wanted prints of that size ("standard" sizes for us are either 6" x
 > 4" or (preferably) 7" x 5").
 >
 > So, my question is, would I take the shots at 2048 x 1536 then use
 > software such as Photoshop or PaintShop Pro to get them down to the
 > required print size, or would I shoot at a lower resolution in the
 > first place (the Optio S is capable of 1600 x 1200, 1024 x 768 and
 > 640 x 480 as well)? Just how do you equate pixels to inches for
 > printing?
 >
 > Cheers,
 >
 > Mogweed.

The higher the resolution you take your picture at the better the print
quality and the degradation due to editing is less apparent. Lower
resolution will increase the number of pictures you can get on a card,
but, image detail will be less apparent. The option to shoot at high
resolution is always good even if you don't use it much.

When it comes to printing there is no need to re-size the image, just
select the option in your printer driver to fit to page.

The number of screen pixels described in your screen resolution is
irrelevant when it comes to printing. When you look at the EXIF info
on a picture you have taken though you will find there not only the
resolution of the picture, but, also the number of pixels per inch,
PPI, which is normally 72 ppi. Dividing your resolution by 72 will
give you an idea of the size the image is displayed at, but, due to
different sizes of screen it is in virtual inches.

Rob<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Megapixels and image size 

Mogweed wrote:
 > I've not yet got a digital camera but I'm being drawn to the Pentax
 > Optio S.
 >
 > I'm not a photographer by any means and phrases like "f-stops", "white
 > balance", "histograms" and such like just leave me cold and mean
 > nothing whatsoever to me - and, I have to admit, I have no particular
 > interest in doing anything to change that situation. I'm strictly a
 > 'point-n-shoot' sort of guy which is why the Pentax appeals to me -
 > small enough to take anywhere and as long as it takes the holiday
 > snaps (both landscape scenery and inside the bars), that's all I want.
 >
 > The thing I need help with is understanding megapixels and print
 > sizes. I know that the Optio S is a 3.2 Mp camera and that that
 > equates to a resolution of 2048 x 1536 and I also know that that will
 > give a good quality print size of 8" x 10" but I've never needed or
 > wanted prints of that size ("standard" sizes for us are either 6" x
 > 4" or (preferably) 7" x 5").
 >
 > So, my question is, would I take the shots at 2048 x 1536 then use
 > software such as Photoshop or PaintShop Pro to get them down to the
 > required print size, or would I shoot at a lower resolution in the
 > first place (the Optio S is capable of 1600 x 1200, 1024 x 768 and
 > 640 x 480 as well)? Just how do you equate pixels to inches for
 > printing?


Mogweed,

Rule of thumb is between 200-300 pixels per inch for top quality. So for a
4x6 inch print you'll need roughly 1200 by 1800 for a nice sharp print.
Truth be told, I've gotten by with as little as 72 pixels per inch on the
final print when pressed to the wall.

Which brings me to sharpening. Most images will benefit from sharpening,
and you should always do some resharpening if you resample the image in
Photoshop.

As time passes, I hope you'll start to be interested in highlight, shadow,
and neutral, so you can be a Curvemeister customer

Take care.
--

Mike Russell
<a style='text-decoration: underline;' href="http://www.curvemeister.com" target="_blank">www.curvemeister.com</a>
<a style='text-decoration: underline;' href="http://www.geigy.2y.net" target="_blank">www.geigy.2y.net</a><!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Megapixels and image size 

"Canopus" <FQJFXARZCCXT.DeleteThis@spammotel.com> wrote in message
news:xn0dgjz21jgoh2000@news.individual.net...
 > Mogweed wrote:
 >
  > > I've not yet got a digital camera but I'm being drawn to the Pentax
  > > Optio S.
  > >
  > > I'm not a photographer by any means and phrases like "f-stops", "white
  > > balance", "histograms" and such like just leave me cold and mean
  > > nothing whatsoever to me - and, I have to admit, I have no particular
  > > interest in doing anything to change that situation. I'm strictly a
  > > 'point-n-shoot' sort of guy which is why the Pentax appeals to me -
  > > small enough to take anywhere and as long as it takes the holiday
  > > snaps (both landscape scenery and inside the bars), that's all I want.
  > >
  > > The thing I need help with is understanding megapixels and print
  > > sizes. I know that the Optio S is a 3.2 Mp camera and that that
  > > equates to a resolution of 2048 x 1536 and I also know that that will
  > > give a good quality print size of 8" x 10" but I've never needed or
  > > wanted prints of that size ("standard" sizes for us are either 6" x
  > > 4" or (preferably) 7" x 5").
  > >
  > > So, my question is, would I take the shots at 2048 x 1536 then use
  > > software such as Photoshop or PaintShop Pro to get them down to the
  > > required print size, or would I shoot at a lower resolution in the
  > > first place (the Optio S is capable of 1600 x 1200, 1024 x 768 and
  > > 640 x 480 as well)? Just how do you equate pixels to inches for
  > > printing?
  > >
  > > Cheers,
  > >
  > > Mogweed.
 >
 > The higher the resolution you take your picture at the better the print
 > quality and the degradation due to editing is less apparent. Lower
 > resolution will increase the number of pictures you can get on a card,
 > but, image detail will be less apparent. The option to shoot at high
 > resolution is always good even if you don't use it much.
 >
 > When it comes to printing there is no need to re-size the image, just
 > select the option in your printer driver to fit to page.
 >
 > The number of screen pixels described in your screen resolution is
 > irrelevant when it comes to printing. When you look at the EXIF info
 > on a picture you have taken though you will find there not only the
 > resolution of the picture, but, also the number of pixels per inch,
 > PPI, which is normally 72 ppi. Dividing your resolution by 72 will
 > give you an idea of the size the image is displayed at, but, due to
 > different sizes of screen it is in virtual inches.
 >
 > Rob

Thanks very much Rob. You've explained it all very well - it all makes sense
to me now )

Cheers mate,

Mogweed.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Megapixels and image size 

On 2 Apr 2004 18:38:55 GMT, "Canopus" wrote:

 >Mogweed wrote:
 >
  >> I've not yet got a digital camera but I'm being drawn to the Pentax
  >> Optio S.
 >
  >> So, my question is, would I take the shots at 2048 x 1536 then use
  >> software such as Photoshop or PaintShop Pro to get them down to the
  >> required print size, or would I shoot at a lower resolution in the
  >> first place (the Optio S is capable of 1600 x 1200, 1024 x 768 and
  >> 640 x 480 as well)? Just how do you equate pixels to inches for
  >> printing?
 >
 >The higher the resolution you take your picture at the better the print
 >quality and the degradation due to editing is less apparent. Lower
 >resolution will increase the number of pictures you can get on a card,
 >but, image detail will be less apparent. The option to shoot at high
 >resolution is always good even if you don't use it much.

Shooting at the highest available resolution is also best if you only
want to print a part of the picture (crop it). If you want to save
space it's always better to turn the compression up a notch - i.e. go
from SuperFine to Fine or whatever Pentax names it's compression
rates - rather than reducing the resolution.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Megapixels and image size 

On Fri, 2 Apr 2004 17:38:20 +0000 (UTC), "Mogweed"
<mogweedTWOTHOUSAND DeleteThis @hotmail.com> vaguely proposed a theory
.......and in reply I say!:
remove ns from my header address to reply via email

300 PPI is considered the extent of human eyesight, and the best print
shops only print at this anyway. 200 PPI is still very good,
especially if the larger print is to be displayed where people are not
going to rub noses with it.

So your 2048*1536 = 7 x 5" at best photo quality, and 10 x 7 at quite
good quality. You could probably get away with even lower res.

But always take the best shots. You may want to crop an image, and
then you start losing resolution very fast.

One thing: Avoid using the "interpolated mode if the camera has it. If
it claims to take a photo that makes the MPi's higher than the
camera's sensor, this is interpolation. It wastes space. It does give
a "cleaner" picture, but you can achieve the same or better in Paint
Shop Pro (recommended at the price!) or whatever and double your shots
per card.

Most printer software, and any decent print shop, will simply print
your photo to fit the page you want (assuming it's the right _shape_!)
Many have little kiosks where you can actually do some cropping etc
onscreen, then print.

If you are not into too much muckin abaht then I would consider
getting stuff printed for you. I have learnt slowly that the average
home printer is _not_ really suitable for printing. The main trouble
found has been longevity of the prints. Then there is colour matching,
expensive paper, inks etc. In the end it may even cost you _more_ to
print your own, if quality is an issue. Do your stuff in editing
software (the fun part), decide what you want printed, then put it on
a CD and get it done is my advice.

 >I've not yet got a digital camera but I'm being drawn to the Pentax Optio S.
 >
 >I'm not a photographer by any means and phrases like "f-stops", "white
 >balance", "histograms" and such like just leave me cold and mean nothing
 >whatsoever to me - and, I have to admit, I have no particular interest in
 >doing anything to change that situation. I'm strictly a 'point-n-shoot' sort
 >of guy which is why the Pentax appeals to me - small enough to take anywhere
 >and as long as it takes the holiday snaps (both landscape scenery and inside
 >the bars), that's all I want.
 >
 >The thing I need help with is understanding megapixels and print sizes. I
 >know that the Optio S is a 3.2 Mp camera and that that equates to a
 >resolution of 2048 x 1536 and I also know that that will give a good quality
 >print size of 8" x 10" but I've never needed or wanted prints of that size
 >("standard" sizes for us are either 6" x 4" or (preferably) 7" x 5").
 >
 >So, my question is, would I take the shots at 2048 x 1536 then use software
 >such as Photoshop or PaintShop Pro to get them down to the required print
 >size, or would I shoot at a lower resolution in the first place (the Optio S
 >is capable of 1600 x 1200, 1024 x 768 and 640 x 480 as well)? Just how do
 >you equate pixels to inches for printing?
 >
 >Cheers,
 >
 >Mogweed.

****************************************************
remove ns from my header address to reply via email

I went on a guided tour not long ago.The guide got
us lost. He was a non-compass mentor.........sorry
.........no I'm not.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Megapixels and image size 

"Old Nick" <nsnfwhite RemoveThis @dodo.net.au> wrote in message
news:7lrr601ruan2vtt2htv9u70pa0lc4lr71p@4ax.com...
 > On Fri, 2 Apr 2004 17:38:20 +0000 (UTC), "Mogweed"
 > <mogweedTWOTHOUSAND RemoveThis @hotmail.com> vaguely proposed a theory
 > ......and in reply I say!:
 > remove ns from my header address to reply via email
 >
 > 300 PPI is considered the extent of human eyesight, and the best print
 > shops only print at this anyway. 200 PPI is still very good,
 > especially if the larger print is to be displayed where people are not
 > going to rub noses with it.
 >
 > So your 2048*1536 = 7 x 5" at best photo quality, and 10 x 7 at quite
 > good quality. You could probably get away with even lower res.
 >
 > But always take the best shots. You may want to crop an image, and
 > then you start losing resolution very fast.
 >
 > One thing: Avoid using the "interpolated mode if the camera has it. If
 > it claims to take a photo that makes the MPi's higher than the
 > camera's sensor, this is interpolation. It wastes space. It does give
 > a "cleaner" picture, but you can achieve the same or better in Paint
 > Shop Pro (recommended at the price!) or whatever and double your shots
 > per card.
 >
 > Most printer software, and any decent print shop, will simply print
 > your photo to fit the page you want (assuming it's the right _shape_!)
 > Many have little kiosks where you can actually do some cropping etc
 > onscreen, then print.
 >
 > If you are not into too much muckin abaht then I would consider
 > getting stuff printed for you. I have learnt slowly that the average
 > home printer is _not_ really suitable for printing. The main trouble
 > found has been longevity of the prints. Then there is colour matching,
 > expensive paper, inks etc. In the end it may even cost you _more_ to
 > print your own, if quality is an issue. Do your stuff in editing
 > software (the fun part), decide what you want printed, then put it on
 > a CD and get it done is my advice.

Thank you very much to all of you who took the time and trouble to reply to
my question. I don't know what's going on with my ISP's newsfeed but most of
your replies have only shown up in the last 30 minutes.

Anyway, once again, cheers folks. Your help is much appreciated.

Mogweed.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Megapixels and image size 

Mike Russell wrote:

 > Rule of thumb is between 200-300 pixels per inch for top quality. So for a
 > 4x6 inch print you'll need roughly 1200 by 1800 for a nice sharp print.


You get a little relief on this for bigger prints depending on your
purpose. A large print is *generally* going to be viewed from a farther
distance, especially if hung on a wall.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Megapixels and image size 

I have done 1 megapixel pictures 11 x 14" and they look fine. It depends on
what kind of sharpness you need for the print. Think of the huge oil
paintings you see but when you get up close they are nothing but bad
brushstrokes. If you want to take aerial spy photos of the guy nextdoor's
wife nude sunbathing then yes the pixel blowup may matter.

The printers "slur" or blend the pixels into gradually changing colours now
and pixelation does not occur like it was known in the old days. At least
not square pixelation anyway.

"dp" <perley RemoveThis @adelphia.net> wrote in message
news:77ydnRoal_DfUvPdRVn-tA@adelphia.com...
 > Mike Russell wrote:
 >
  > > Rule of thumb is between 200-300 pixels per inch for top quality. So for
a
  > > 4x6 inch print you'll need roughly 1200 by 1800 for a nice sharp print.
 >
 >
 > You get a little relief on this for bigger prints depending on your
 > purpose. A large print is *generally* going to be viewed from a farther
 > distance, especially if hung on a wall.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Megapixels and image size 

Mogweed typed:

 > I've not yet got a digital camera but I'm being drawn to the Pentax
 > Optio S.
 >
 > I'm not a photographer by any means and phrases like "f-stops", "white
 > balance", "histograms" and such like just leave me cold and mean
 > nothing whatsoever to me - and, I have to admit, I have no particular
 > interest in doing anything to change that situation. I'm strictly a
 > 'point-n-shoot' sort of guy which is why the Pentax appeals to me -
 > small enough to take anywhere and as long as it takes the holiday
 > snaps (both landscape scenery and inside the bars), that's all I want.
 >



That's what i said when i bought my first camera. I didn't know much about
it, just wanted point-and-shoot. But after a year or so, things become
different. You come up with pics, which are too dark, wrong colors, wrong
whatever... and you'd like to have some manual control.
Remember, all cameras do have auto setup, like you want. But some of them
also have the possibility of setting things manually. Especially look for so
called sport setting - if camera doesn't have it, you won't be able to shoot
fast moving things.





 > The thing I need help with is understanding megapixels and print
 > sizes. I know that the Optio S is a 3.2 Mp camera and that that
 > equates to a resolution of 2048 x 1536 and I also know that that will
 > give a good quality print size of 8" x 10" but I've never needed or
 > wanted prints of that size ("standard" sizes for us are either 6" x
 > 4" or (preferably) 7" x 5").
 >
 > So, my question is, would I take the shots at 2048 x 1536 then use
 > software such as Photoshop or PaintShop Pro to get them down to the
 > required print size, or would I shoot at a lower resolution in the
 > first place (the Optio S is capable of 1600 x 1200, 1024 x 768 and
 > 640 x 480 as well)? Just how do you equate pixels to inches for
 > printing?
 >
 > Cheers,
 >
 > Mogweed.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Megapixels and image size 

Mogweed wrote:

 >
 > Thank you very much to all of you who took the time and trouble to
 > reply to my question. I don't know what's going on with my ISP's
 > newsfeed but most of your replies have only shown up in the last 30
 > minutes.
 >
 > Anyway, once again, cheers folks. Your help is much appreciated.
 >
 > Mogweed.

Try out news.individual.net, I haven't had any trouble like that since
changing to them, but, was always having problems when I used to use my
IPs news-server.

Rob<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Megapixels and image size 

Although I'm new at digital photography, I use the maximum resolution on
my camera. You never know when you may get that special shot that
deserves a large poster print. I bought 4 extra memory cards just because.



Mogweed wrote:
 > I've not yet got a digital camera but I'm being drawn to the Pentax Optio S.
 >
 > I'm not a photographer by any means and phrases like "f-stops", "white
 > balance", "histograms" and such like just leave me cold and mean nothing
 > whatsoever to me - and, I have to admit, I have no particular interest in
 > doing anything to change that situation. I'm strictly a 'point-n-shoot' sort
 > of guy which is why the Pentax appeals to me - small enough to take anywhere
 > and as long as it takes the holiday snaps (both landscape scenery and inside
 > the bars), that's all I want.
 >
 > The thing I need help with is understanding megapixels and print sizes. I
 > know that the Optio S is a 3.2 Mp camera and that that equates to a
 > resolution of 2048 x 1536 and I also know that that will give a good quality
 > print size of 8" x 10" but I've never needed or wanted prints of that size
 > ("standard" sizes for us are either 6" x 4" or (preferably) 7" x 5").
 >
 > So, my question is, would I take the shots at 2048 x 1536 then use software
 > such as Photoshop or PaintShop Pro to get them down to the required print
 > size, or would I shoot at a lower resolution in the first place (the Optio S
 > is capable of 1600 x 1200, 1024 x 768 and 640 x 480 as well)? Just how do
 > you equate pixels to inches for printing?
 >
 > Cheers,
 >
 > Mogweed.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Megapixels and image size 

On Sat, 3 Apr 2004 19:35:49 +0200, "SleeperMan"
<SleeperMan.TakeThisOut@too.sleepy> vaguely proposed a theory
.......and in reply I say!:
remove ns from my header address to reply via email

I second that, although my first camera had a separate handheld light
meter! _That_ was a manual camera! <G>

But taking photos is so fascinating, and control can be so critical
once understood, that some sort of further control is essential. It
ain't that hard. I read a comment that photography's hardest part is
"seeing" the picture, and all the other stuff is just technique <G>.
But if you "see" a picture, and your camera simply can't handle it so
the result is crappy, it can be very disappointing.

The Optio S seems a good camera, with quality, very small size and
simplicity, from what Steve's writes. I would like to know how much
flex the User Auto setting allows. That is where you may be able to
set up special situations. Unfortunately, Steve's doesn't say

It may be worth asking on Steve's Forums, in the apporopriate area.
Somebody will know. They are not a bad bunch.


 >That's what i said when i bought my first camera. I didn't know much about
 >it, just wanted point-and-shoot. But after a year or so, things become
 >different. You come up with pics, which are too dark, wrong colors, wrong
 >whatever... and you'd like to have some manual control.
 >Remember, all cameras do have auto setup, like you want. But some of them
 >also have the possibility of setting things manually. Especially look for so
 >called sport setting - if camera doesn't have it, you won't be able to shoot
 >fast moving things.
 >
 >
 >
 >
 >
  >> The thing I need help with is understanding megapixels and print
  >> sizes. I know that the Optio S is a 3.2 Mp camera and that that
  >> equates to a resolution of 2048 x 1536 and I also know that that will
  >> give a good quality print size of 8" x 10" but I've never needed or
  >> wanted prints of that size ("standard" sizes for us are either 6" x
  >> 4" or (preferably) 7" x 5").
  >>
  >> So, my question is, would I take the shots at 2048 x 1536 then use
  >> software such as Photoshop or PaintShop Pro to get them down to the
  >> required print size, or would I shoot at a lower resolution in the
  >> first place (the Optio S is capable of 1600 x 1200, 1024 x 768 and
  >> 640 x 480 as well)? Just how do you equate pixels to inches for
  >> printing?
  >>
  >> Cheers,
  >>
  >> Mogweed.
 >
 >

****************************************************
remove ns from my header address to reply via email

I went on a guided tour not long ago.The guide got
us lost. He was a non-compass mentor.........sorry
.........no I'm not.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Megapixels and image size 

As usual Nick, good points....agree

Eddie



"Old Nick" <nsnfwhite.RemoveThis@dodo.net.au> wrote in message
news:7lrr601ruan2vtt2htv9u70pa0lc4lr71p@4ax.com...
 > On Fri, 2 Apr 2004 17:38:20 +0000 (UTC), "Mogweed"
 > <mogweedTWOTHOUSAND.RemoveThis@hotmail.com> vaguely proposed a theory
 > ......and in reply I say!:
 > remove ns from my header address to reply via email
 >
 > 300 PPI is considered the extent of human eyesight, and the best print
 > shops only print at this anyway. 200 PPI is still very good,
 > especially if the larger print is to be displayed where people are not
 > going to rub noses with it.
 >
 > So your 2048*1536 = 7 x 5" at best photo quality, and 10 x 7 at quite
 > good quality. You could probably get away with even lower res.
 >
 > But always take the best shots. You may want to crop an image, and
 > then you start losing resolution very fast.
 >
 > One thing: Avoid using the "interpolated mode if the camera has it. If
 > it claims to take a photo that makes the MPi's higher than the
 > camera's sensor, this is interpolation. It wastes space. It does give
 > a "cleaner" picture, but you can achieve the same or better in Paint
 > Shop Pro (recommended at the price!) or whatever and double your shots
 > per card.
 >
 > Most printer software, and any decent print shop, will simply print
 > your photo to fit the page you want (assuming it's the right _shape_!)
 > Many have little kiosks where you can actually do some cropping etc
 > onscreen, then print.
 >
 > If you are not into too much muckin abaht then I would consider
 > getting stuff printed for you. I have learnt slowly that the average
 > home printer is _not_ really suitable for printing. The main trouble
 > found has been longevity of the prints. Then there is colour matching,
 > expensive paper, inks etc. In the end it may even cost you _more_ to
 > print your own, if quality is an issue. Do your stuff in editing
 > software (the fun part), decide what you want printed, then put it on
 > a CD and get it done is my advice.
 >
  > >I've not yet got a digital camera but I'm being drawn to the Pentax Optio
S.
  > >
  > >I'm not a photographer by any means and phrases like "f-stops", "white
  > >balance", "histograms" and such like just leave me cold and mean nothing
  > >whatsoever to me - and, I have to admit, I have no particular interest in
  > >doing anything to change that situation. I'm strictly a 'point-n-shoot'
sort
  > >of guy which is why the Pentax appeals to me - small enough to take
anywhere
  > >and as long as it takes the holiday snaps (both landscape scenery and
inside
  > >the bars), that's all I want.
  > >
  > >The thing I need help with is understanding megapixels and print sizes. I
  > >know that the Optio S is a 3.2 Mp camera and that that equates to a
  > >resolution of 2048 x 1536 and I also know that that will give a good
quality
  > >print size of 8" x 10" but I've never needed or wanted prints of that
size
  > >("standard" sizes for us are either 6" x 4" or (preferably) 7" x 5").
  > >
  > >So, my question is, would I take the shots at 2048 x 1536 then use
software
  > >such as Photoshop or PaintShop Pro to get them down to the required print
  > >size, or would I shoot at a lower resolution in the first place (the
Optio S
  > >is capable of 1600 x 1200, 1024 x 768 and 640 x 480 as well)? Just how do
  > >you equate pixels to inches for printing?
  > >
  > >Cheers,
  > >
  > >Mogweed.
 >
 > ****************************************************
 > remove ns from my header address to reply via email
 >
 > I went on a guided tour not long ago.The guide got
 > us lost. He was a non-compass mentor.........sorry
 > ........no I'm not.<!-- ~MESSAGE_AFTER~ -->
 >> Stay informed about: Megapixels and image size