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Re: Image Size and Compression.

 
 
ray
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      07-30-2010
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.
 
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Ryan McGinnis
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      07-30-2010
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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/se...=Ryan+McGinnis

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Dave Cohen
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      07-30-2010
Ryan McGinnis wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> 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).
 
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ray
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      07-30-2010
On Fri, 30 Jul 2010 09:56:21 -0500, Ryan McGinnis wrote:

> -----BEGIN PGP SIGNED MESSAGE-----
> 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.


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/se...=Ryan+McGinnis
>
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Ryan McGinnis
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      07-30-2010
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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/se...=Ryan+McGinnis

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Peter
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      07-30-2010
"Dave Cohen" <(E-Mail Removed)> wrote in message
news:i2uvmg$dn3$(E-Mail Removed)-september.org...

> 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).



Try Corel PaintShop Photo Pro. Corel sells it for $59.9. It is excellent
value and does not have a large learning curve.
In the interests of full disclosure, I am a Corel partner, but only for
WordPerfect.

--
Peter

 
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David J Taylor
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      07-30-2010
"bobwilliams" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
[]
> 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


By matching the compression to both the source and the eye/brain
characteristics - i.e. limiting the amount of detail where the eye can't
see it. JPEG is generally very well designed for its intended use.

Cheers,
David

 
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Peter
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      07-30-2010
"bobwilliams" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> ray wrote:


>> 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.


It depends on the image and viewing method.
As a general rule: (Yes there may be some exceptions, depending on the
particular image.)
If you are talking about digital viewing, you may not even notice the
degradation. If set up for magazine printing, maybe there would be some
noticeable degradation. For photo quality ink jet printing depends on the
size. the larger the print, the more you will notice the degradation.

IOW there is no one definitive answer that fits all cases.
--
Peter

 
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Wolfgang Weisselberg
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      07-31-2010
Ryan McGinnis <(E-Mail Removed)> wrote:

> 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.


A proper backup concept will cost much more than $150.

-Wolfgang
 
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Ryan McGinnis
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      07-31-2010
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On 7/31/2010 3:42 PM, Wolfgang Weisselberg wrote:
> Ryan McGinnis <(E-Mail Removed)> wrote:
>
>> 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.

>
> A proper backup concept will cost much more than $150.


Depends how you run it. I go with one primary drive and one secondary
drive for temp backups of new stuff. Every month or so I archive the
new stuff to two sets of DVDs, delete it off of the secondary drive, and
place one set of DVDs in a bank vault. DVDs are pretty cheap.


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

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