From: Ryan McGinnis on
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On 7/30/2010 9:12 AM, ray wrote:
> On Fri, 30 Jul 2010 01:25:37 -0700, bobwilliams wrote:
>
>> Let's assume I have a 10MP camera
>> My sensor is say, 3650 X 2740 pixels. But say I want to create an image
>> at 1825 x 1370 pixels. How does the camera actually reduce the 5.0MPs to
>> 2.5MPs Does it choose groups of 4 pixels and somehow average them out to
>> groups of 1 pixel each?
>> How does this process differ from compressing the 10MP image by a factor
>> of 4.
>> I know that in one case the image SIZE is reduced (as well as the file
>> size) whereas in the other case, the image SIZE remains the same but the
>> file size is reduced.
>> How exactly does each process affect the appearance of say an 8x10
>> print. Bob Williams
>
> I would imagine you are talking about JPEG compression here. Suggest you
> experiment a little with your favourite photo manipulation software.
> You'll find that most images can be very highly compressed without any
> noticeable degredation. The same is not true for dropping resolution.

I'd take a different approach: why try to reduce filesize? Storage is
incredibly cheap and getting cheaper by the hour. If you are not
shooting RAW, a terabyte drive will hold more photos than you're likely
to take in your lifetime on a 10MP camera, and they run around $150.
You can't go back and re-take your photo in a higher resolution or with
less compression, but you can always buy more hard drives.

- --
- -Ryan McGinnis
The BIG Storm Picture -- http://bigstormpicture.com
Vortex-2 image licensing at http://vortex-2.com
Getty: http://www.gettyimages.com/search/search.aspx?artist=Ryan+McGinnis

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From: Dave Cohen on
Ryan McGinnis wrote:
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> Hash: SHA1
>
> On 7/30/2010 9:12 AM, ray wrote:
>> On Fri, 30 Jul 2010 01:25:37 -0700, bobwilliams wrote:
>>
>>> Let's assume I have a 10MP camera
>>> My sensor is say, 3650 X 2740 pixels. But say I want to create an image
>>> at 1825 x 1370 pixels. How does the camera actually reduce the 5.0MPs to
>>> 2.5MPs Does it choose groups of 4 pixels and somehow average them out to
>>> groups of 1 pixel each?
>>> How does this process differ from compressing the 10MP image by a factor
>>> of 4.
>>> I know that in one case the image SIZE is reduced (as well as the file
>>> size) whereas in the other case, the image SIZE remains the same but the
>>> file size is reduced.
>>> How exactly does each process affect the appearance of say an 8x10
>>> print. Bob Williams
>> I would imagine you are talking about JPEG compression here. Suggest you
>> experiment a little with your favourite photo manipulation software.
>> You'll find that most images can be very highly compressed without any
>> noticeable degredation. The same is not true for dropping resolution.
>
> I'd take a different approach: why try to reduce filesize? Storage is
> incredibly cheap and getting cheaper by the hour. If you are not
> shooting RAW, a terabyte drive will hold more photos than you're likely
> to take in your lifetime on a 10MP camera, and they run around $150.
> You can't go back and re-take your photo in a higher resolution or with
> less compression, but you can always buy more hard drives.
>
> - --
The op beat me to the same question. My concern was not with file size
but with noise. Canon do use a lower resolution when higher iso is
selected by them for low light scene settings. I'll just run a bunch of
test shots including using the noise reduction layer in PhotoPlus (could
never afford PS).
From: ray on
On Fri, 30 Jul 2010 09:56:21 -0500, Ryan McGinnis wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
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> On 7/30/2010 9:12 AM, ray wrote:
>> On Fri, 30 Jul 2010 01:25:37 -0700, bobwilliams wrote:
>>
>>> Let's assume I have a 10MP camera
>>> My sensor is say, 3650 X 2740 pixels. But say I want to create an
>>> image at 1825 x 1370 pixels. How does the camera actually reduce the
>>> 5.0MPs to 2.5MPs Does it choose groups of 4 pixels and somehow average
>>> them out to groups of 1 pixel each?
>>> How does this process differ from compressing the 10MP image by a
>>> factor of 4.
>>> I know that in one case the image SIZE is reduced (as well as the file
>>> size) whereas in the other case, the image SIZE remains the same but
>>> the file size is reduced.
>>> How exactly does each process affect the appearance of say an 8x10
>>> print. Bob Williams
>>
>> I would imagine you are talking about JPEG compression here. Suggest
>> you experiment a little with your favourite photo manipulation
>> software. You'll find that most images can be very highly compressed
>> without any noticeable degredation. The same is not true for dropping
>> resolution.
>
> I'd take a different approach: why try to reduce filesize? Storage is
> incredibly cheap and getting cheaper by the hour. If you are not
> shooting RAW, a terabyte drive will hold more photos than you're likely
> to take in your lifetime on a 10MP camera, and they run around $150. You
> can't go back and re-take your photo in a higher resolution or with less
> compression, but you can always buy more hard drives.

I'm not arguing about the cost of storage - I'm answering a question.
There could be any number of reasons to concern oneself with file size -
for one, when you're doing web pages. Huge files can take a long time to
download even with broadband connection - and not EVERYONE has high speed
connections.


>
> - --
> - -Ryan McGinnis
> The BIG Storm Picture -- http://bigstormpicture.com Vortex-2 image
> licensing at http://vortex-2.com Getty:
> http://www.gettyimages.com/search/search.aspx?artist=Ryan+McGinnis
>
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From: Ryan McGinnis on
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On 7/30/2010 12:50 PM, ray wrote:

>> I'm not arguing about the cost of storage - I'm answering a question.
>> There could be any number of reasons to concern oneself with file size -
>> for one, when you're doing web pages. Huge files can take a long time to
>> download even with broadband connection - and not EVERYONE has high speed
>> connections.

That's true -- though I guess I just assumed that the easiest method was
to take full res photos and downsample them with software. But it's
true that not all users will ever need the high-res shots for any
reason. This might come into play with some of those wireless shooting
setups, too, where bandwidth is at a premium.

- --
- -Ryan McGinnis
The BIG Storm Picture -- http://bigstormpicture.com
Vortex-2 image licensing at http://vortex-2.com
Getty: http://www.gettyimages.com/search/search.aspx?artist=Ryan+McGinnis

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From: bobwilliams on
ray wrote:
> On Fri, 30 Jul 2010 01:25:37 -0700, bobwilliams wrote:
>
>> Let's assume I have a 10MP camera
>> My sensor is say, 3650 X 2740 pixels. But say I want to create an image
>> at 1825 x 1370 pixels. How does the camera actually reduce the 5.0MPs to
>> 2.5MPs Does it choose groups of 4 pixels and somehow average them out to
>> groups of 1 pixel each?
>> How does this process differ from compressing the 10MP image by a factor
>> of 4.
>> I know that in one case the image SIZE is reduced (as well as the file
>> size) whereas in the other case, the image SIZE remains the same but the
>> file size is reduced.
>> How exactly does each process affect the appearance of say an 8x10
>> print. Bob Williams
>
> I would imagine you are talking about JPEG compression here. Suggest you
> experiment a little with your favourite photo manipulation software.
> You'll find that most images can be very highly compressed without any
> noticeable degredation. The same is not true for dropping resolution.
That is what I have noticed too. I was just wondering how such good
quality was retained after losing so much image information either by
compression or image size reduction.
Bob