A Photography forum. PhotoBanter.com

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » PhotoBanter.com forum » Digital Photography » Digital Photography
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Compression in JPEG files in digital cameras



 
 
Thread Tools Display Modes
  #1  
Old August 18th 07, 07:55 PM posted to rec.photo.digital,uk.rec.photo.misc
[email protected]
external usenet poster
 
Posts: 182
Default Compression in JPEG files in digital cameras

I need some help in explaining the JPEG compression feature in digital
cameras. My camera (which likely is similar to most others) has the
feature to compress the photo JPEG files in the storage card. It also
has the choice to have different pixel sizes (example: 3000x2250,
2000x1500, 1024x768, etc). What is the difference of the above two
features? If you store a 3000x2250 pixel data in compressed mode,
does it loose its quality? Can it be re-instated to full uncompressed
size without loosing photo quality?. When I compressed the data, it
will fit more pictures in a single storage card. But, is it the same
if I choose 2000x1500 pixel and no compression instead?
Thanks for info.

  #2  
Old August 18th 07, 08:29 PM posted to rec.photo.digital,uk.rec.photo.misc
harrogate3[_2_]
external usenet poster
 
Posts: 10
Default Compression in JPEG files in digital cameras


wrote in message
ups.com...
I need some help in explaining the JPEG compression feature in

digital
cameras. My camera (which likely is similar to most others) has the
feature to compress the photo JPEG files in the storage card. It

also
has the choice to have different pixel sizes (example: 3000x2250,
2000x1500, 1024x768, etc). What is the difference of the above two
features? If you store a 3000x2250 pixel data in compressed mode,
does it loose its quality? Can it be re-instated to full

uncompressed
size without loosing photo quality?. When I compressed the data, it
will fit more pictures in a single storage card. But, is it the same
if I choose 2000x1500 pixel and no compression instead?
Thanks for info.



Don't ask much, do you?

Jpg is a lossy form of saving the picture - Google on 'explanation of
jpg' and it will give you the detail - as distinct from compressed per
se. As you have lost picture info you cannot get it back, so there is
no way to regenerate the original intact. If you want to save in a
non-compressed format you need to use TIFF (OK it is slightly
compressed) or better still RAW which is just the raw data off the
sensor without adjustment.

The differences in resolution affect file size and quality of
reproduction. 3000x2250 is about 6.7Mp, 2000x1500 is 3Mp, etc. For
'normal' printing at full frame (i.e. without cropping) 3Mp will
produce an acceptable colour picture at A4 or thereabouts. For most
day-to-day use 5Mp is enough, 6Mp is really the limit for a compact.
If you go much higher than that you start to get digital noise in
saturated colours due mainly to thermal effects in the sensor. Another
point that is often missed is that the lenses on many compacts -
particularly at the cheaper end of the market - often do not have the
resolution in themselves to match the resolution of the sensor.

In a nutshell, use RAW or TIFF if your camera has it, otherwise go for
the best quality that the camera can provide - memory cards are dirt
cheap these days.


--
Woody

harrogate3 at ntlworld dot com


  #3  
Old August 18th 07, 08:33 PM posted to rec.photo.digital,uk.rec.photo.misc
Trev
external usenet poster
 
Posts: 81
Default Compression in JPEG files in digital cameras


wrote in message
ups.com...
I need some help in explaining the JPEG compression feature in digital
cameras. My camera (which likely is similar to most others) has the
feature to compress the photo JPEG files in the storage card. It also
has the choice to have different pixel sizes (example: 3000x2250,
2000x1500, 1024x768, etc). What is the difference of the above two
features? If you store a 3000x2250 pixel data in compressed mode,
does it loose its quality? Can it be re-instated to full uncompressed
size without loosing photo quality?. When I compressed the data, it
will fit more pictures in a single storage card. But, is it the same
if I choose 2000x1500 pixel and no compression instead?
Thanks for info.

All jpegs have some compression. In simple terms, because I am, jpeg saving
examines the image in 16 pixel groups and assess how much alike the colours
are. Just how much the need to be is the compression factor high compression
means they dont have to be as close as low compression. What it does now it
save one pixel of that colour and notes where the simler pixels are then
dumps them.
When you reopen the image the missing pixels are replaced with copies of
that saved one.

Images with large expenses of simler colour like sky and sand compress down
to a smaller file size at the same level of compression than a image busy in
fine detail. This happens each time you save as jpeg, losing some detail
each time until the image is ruined so dont keep making changes and resaving
none of this Makes any difference the dimensions such as 3000 x 2000 adding
the compression and smaller dimensions will make a mush smaller file. When
it comes to printing the more pixels the better if you want a larger print
as we use a print scaling factor referred to as ppi pixels per inch. That
how many pixels we pack into a SQ inch of paper. for a print that we will
inspect at upto arms length we need 200ppi. this means the finest detail in
the print will be 200th of an inch. so for a 10 x 8 print we need 10 x 200
= 2000 pixels wide by 8 x 200 = 1600 pixels high.
I hope that is of some help


  #4  
Old August 18th 07, 08:38 PM posted to rec.photo.digital,uk.rec.photo.misc
A.Lee
external usenet poster
 
Posts: 6
Default Compression in JPEG files in digital cameras

wrote:

I need some help in explaining the JPEG compression feature in digital
cameras. My camera (which likely is similar to most others) has the
feature to compress the photo JPEG files in the storage card.
It also has the choice to have different pixel sizes (example:
3000x2250, 2000x1500, 1024x768, etc). What is the difference of the
above two features?


Smaller files size/pixel size equals poorer quality.On the other hand,
it means more pics on the card. With the cost of memory so low now, it
isnt really much of a feature now, as there is no point in saving in
smaller formats.

If you store a 3000x2250 pixel data in compressed mode,
does it lose its quality?


Yes. Any system that saves as jpeg will be a compromise between file
size and quality.

Can it be re-instated to full uncompressed size without loosing photo
quality?.


No.

When I compressed the data, it will fit more pictures in a single
storage card. But, is it the same if I choose 2000x1500 pixel and no
compression instead?


No. As above, if you save as a jpeg, you will lose quality. For the best
quality, pics should be saved in RAW format, or any of the other
proprietary no-loss formats that camera makers use.
Alan.

--
To reply by e-mail, change the ' + ' to 'plus'.
  #5  
Old August 18th 07, 08:38 PM posted to rec.photo.digital,uk.rec.photo.misc
ray
external usenet poster
 
Posts: 2,278
Default Compression in JPEG files in digital cameras

On Sat, 18 Aug 2007 11:55:45 -0700, aniramca wrote:

I need some help in explaining the JPEG compression feature in digital
cameras. My camera (which likely is similar to most others) has the
feature to compress the photo JPEG files in the storage card. It also
has the choice to have different pixel sizes (example: 3000x2250,
2000x1500, 1024x768, etc). What is the difference of the above two
features? If you store a 3000x2250 pixel data in compressed mode,
does it loose its quality? Can it be re-instated to full uncompressed
size without loosing photo quality?. When I compressed the data, it
will fit more pictures in a single storage card. But, is it the same
if I choose 2000x1500 pixel and no compression instead?
Thanks for info.


It will uncompress to the full resolution - however it will not be an
exact replica of the original image. JPEG is a 'lossy' compression
algorithm - meaning that some detail is lost in the act of compressing the
data. There are 'lossless' compression schemes as well, but the level of
compression with them is generally considerably less. From a practical
standpoint, you can do a lot of compression on a JPEG image before you see
noticeable loss of information. Before I got a camera capable of saving
RAW images, I always chose the highest resolution and the smallest amount
of compressin on JPEG images - now I simply save nearly everything in RAW
- even though it does take a lot of space. Memory cards are very cheap now
- IMHO it is better to get some extra cards and save everything using the
best method possible. I currently have 2-1gb cards and 1-2gb card for my
5mp camera - they run around $15 and $30 respectively.

  #6  
Old August 19th 07, 12:53 AM posted to rec.photo.digital,uk.rec.photo.misc
Dave Cohen
external usenet poster
 
Posts: 841
Default Compression in JPEG files in digital cameras

ray wrote:
On Sat, 18 Aug 2007 11:55:45 -0700, aniramca wrote:

I need some help in explaining the JPEG compression feature in digital
cameras. My camera (which likely is similar to most others) has the
feature to compress the photo JPEG files in the storage card. It also
has the choice to have different pixel sizes (example: 3000x2250,
2000x1500, 1024x768, etc). What is the difference of the above two
features? If you store a 3000x2250 pixel data in compressed mode,
does it loose its quality? Can it be re-instated to full uncompressed
size without loosing photo quality?. When I compressed the data, it
will fit more pictures in a single storage card. But, is it the same
if I choose 2000x1500 pixel and no compression instead?
Thanks for info.


It will uncompress to the full resolution - however it will not be an
exact replica of the original image. JPEG is a 'lossy' compression
algorithm - meaning that some detail is lost in the act of compressing the
data. There are 'lossless' compression schemes as well, but the level of
compression with them is generally considerably less. From a practical
standpoint, you can do a lot of compression on a JPEG image before you see
noticeable loss of information. Before I got a camera capable of saving
RAW images, I always chose the highest resolution and the smallest amount
of compressin on JPEG images - now I simply save nearly everything in RAW
- even though it does take a lot of space. Memory cards are very cheap now
- IMHO it is better to get some extra cards and save everything using the
best method possible. I currently have 2-1gb cards and 1-2gb card for my
5mp camera - they run around $15 and $30 respectively.


The resolution refers to the amount of detail captured by the sensor and
saved before any compression (if any) is applied. Ultimately it will
translate into how large an image you can print. Initially, large prints
will lose resolution, continued enlargement will exhibit pixelation.
I always shoot at maximum resolution (5mp in my case). There will be
instances when lower resolutions are ultimately desired for web use or
email, but this can all be done later. This has little to do with how
the file is saved.

Jpeg compression reduces file size from whatever lossless format the
camera uses to a more manageable size. Usually, you are given a choice
of 3 settings with names like fine, super fine and normal. I can't for
the life of me ever see any difference between fine (the default) and
super fine except a very large size difference, so I use default and if
others disagree, as I'm sure they will, that's ok, but I don't want to
hear about it.
As mentioned elsewhere, the algorithm works by cleverly looking for
adjacent pixels of close color match and combining them. As you increase
the compression the quality goes down, but the appearance is quite
different from low resolution.
Fortunately you can easily see how this works. Save a file at least
compression, then use something like Irfanview to output a series of
files at decreasing quality (increasing compression). At some point you
will begin to notice the deterioration. Some software will actually show
you a preview of how the image will look at different degrees of
compression before you save.
I always save the original from the camera and avoid editing a modified
jpeg a second or more time.
Tiff and raw are lossless formats, but only some p&s's even offer that
option, presumably since the audience for a p&s isn't likely to want to
do the post processing involved, but there are exceptions.
Dave Cohen

  #7  
Old August 19th 07, 03:42 AM posted to rec.photo.digital,uk.rec.photo.misc
ray
external usenet poster
 
Posts: 2,278
Default Compression in JPEG files in digital cameras

On Sat, 18 Aug 2007 23:53:50 +0000, Dave Cohen wrote:

ray wrote:
On Sat, 18 Aug 2007 11:55:45 -0700, aniramca wrote:

I need some help in explaining the JPEG compression feature in digital
cameras. My camera (which likely is similar to most others) has the
feature to compress the photo JPEG files in the storage card. It also
has the choice to have different pixel sizes (example: 3000x2250,
2000x1500, 1024x768, etc). What is the difference of the above two
features? If you store a 3000x2250 pixel data in compressed mode,
does it loose its quality? Can it be re-instated to full uncompressed
size without loosing photo quality?. When I compressed the data, it
will fit more pictures in a single storage card. But, is it the same
if I choose 2000x1500 pixel and no compression instead?
Thanks for info.


It will uncompress to the full resolution - however it will not be an
exact replica of the original image. JPEG is a 'lossy' compression
algorithm - meaning that some detail is lost in the act of compressing the
data. There are 'lossless' compression schemes as well, but the level of
compression with them is generally considerably less. From a practical
standpoint, you can do a lot of compression on a JPEG image before you see
noticeable loss of information. Before I got a camera capable of saving
RAW images, I always chose the highest resolution and the smallest amount
of compressin on JPEG images - now I simply save nearly everything in RAW
- even though it does take a lot of space. Memory cards are very cheap now
- IMHO it is better to get some extra cards and save everything using the
best method possible. I currently have 2-1gb cards and 1-2gb card for my
5mp camera - they run around $15 and $30 respectively.


The resolution refers to the amount of detail captured by the sensor and
saved before any compression (if any) is applied. Ultimately it will
translate into how large an image you can print. Initially, large prints
will lose resolution, continued enlargement will exhibit pixelation.
I always shoot at maximum resolution (5mp in my case). There will be
instances when lower resolutions are ultimately desired for web use or
email, but this can all be done later. This has little to do with how
the file is saved.


Other things being equal, a jpeg saved with more compression will show
some 'blockiness' at a lower magnification than one saved with less
compression i.e. higher jpeg quality.


Jpeg compression reduces file size from whatever lossless format the
camera uses to a more manageable size. Usually, you are given a choice
of 3 settings with names like fine, super fine and normal. I can't for
the life of me ever see any difference between fine (the default) and
super fine except a very large size difference, so I use default and if
others disagree, as I'm sure they will, that's ok, but I don't want to
hear about it.
As mentioned elsewhere, the algorithm works by cleverly looking for
adjacent pixels of close color match and combining them. As you increase
the compression the quality goes down, but the appearance is quite
different from low resolution.
Fortunately you can easily see how this works. Save a file at least
compression, then use something like Irfanview to output a series of
files at decreasing quality (increasing compression). At some point you
will begin to notice the deterioration. Some software will actually show
you a preview of how the image will look at different degrees of
compression before you save.
I always save the original from the camera and avoid editing a modified
jpeg a second or more time.
Tiff and raw are lossless formats, but only some p&s's even offer that
option, presumably since the audience for a p&s isn't likely to want to
do the post processing involved, but there are exceptions.
Dave Cohen


  #8  
Old August 19th 07, 09:09 AM posted to rec.photo.digital,uk.rec.photo.misc
Bucky
external usenet poster
 
Posts: 115
Default Compression in JPEG files in digital cameras

On Aug 18, 11:55 am, wrote:
I need some help in explaining the JPEG compression feature in digital
cameras. My camera (which likely is similar to most others) has the
feature to compress the photo JPEG files in the storage card. It also
has the choice to have different pixel sizes (example: 3000x2250,
2000x1500, 1024x768, etc). What is the difference of the above two
features?


Tough question. My theory is that, assuming that jpeg compression is
optimized, that file size will be be the determination of image
quality. So, if you are wondering which will have a better image
quality: medium resolution at max quality (lowest compression) vs max
resolution at med quality (med compression), I would guess that the
one with a larger file size.

Of course, you should also do a sanity check by viewing both files
resampled to the same resolution (with antialiasing). For example, to
your screen resolution (1024x768 or whatever).

  #9  
Old August 19th 07, 09:34 AM posted to rec.photo.digital,uk.rec.photo.misc
Ron Hunter
external usenet poster
 
Posts: 4,064
Default Compression in JPEG files in digital cameras

wrote:
I need some help in explaining the JPEG compression feature in digital
cameras. My camera (which likely is similar to most others) has the
feature to compress the photo JPEG files in the storage card. It also
has the choice to have different pixel sizes (example: 3000x2250,
2000x1500, 1024x768, etc). What is the difference of the above two
features? If you store a 3000x2250 pixel data in compressed mode,
does it loose its quality? Can it be re-instated to full uncompressed
size without loosing photo quality?. When I compressed the data, it
will fit more pictures in a single storage card. But, is it the same
if I choose 2000x1500 pixel and no compression instead?
Thanks for info.

Most P&S cameras produce .jpg picture files, which are ALWAYS compressed
to some degree, and they also do lose some picture information, which is
why the JPEG compression system is labeled 'lossy'. In the practical
sense, if the camera has multiple compression settings, select the
lowest compression value, usually expressed as 'fine', or 'super fine',
and the highest resolution setting. Memory cards are VERY cheap these
days, so there is really no reason to skimp on resolution, or compress
excessively.
  #10  
Old August 19th 07, 09:35 AM posted to rec.photo.digital
David J Taylor[_4_]
external usenet poster
 
Posts: 1,151
Default Compression in JPEG files in digital cameras

Bucky wrote:
On Aug 18, 11:55 am, wrote:
I need some help in explaining the JPEG compression feature in
digital cameras. My camera (which likely is similar to most others)
has the feature to compress the photo JPEG files in the storage
card. It also has the choice to have different pixel sizes (example:
3000x2250, 2000x1500, 1024x768, etc). What is the difference of the
above two features?


Tough question. My theory is that, assuming that jpeg compression is
optimized, that file size will be be the determination of image
quality. So, if you are wondering which will have a better image
quality: medium resolution at max quality (lowest compression) vs max
resolution at med quality (med compression), I would guess that the
one with a larger file size.

Of course, you should also do a sanity check by viewing both files
resampled to the same resolution (with antialiasing). For example, to
your screen resolution (1024x768 or whatever).


What I have found in practice is that using the maximum resolution with
the "normal" quality setting can beat the lower resolution with the "fine"
quality setting. Of course, this is highly camera dependant, and you
should test for yourself.

My theory behind this is that running at the maximum resolution, you are
more limited by the MTF of the lens and other components, so there is
relatively less high-frequency component in the image, and that the JPEG
algorithm does not need to work so hard to compress the data, and can
therefore provide a higher quality image.

So my recommendation to the OP is to stick with maximum resolution (3000 x
2250), and to make a series of test photos at the different quality (JPEG
compression) levels, and see where you want to draw the line between file
size and image quality. Include both sharp edges and subtly coloured (or
even varying grey) areas in your test image. I have found that the
"normal" quality setting is satisfactory on the Nikon cameras I have
owned - your camera and image quality requirements may differ.

Nikon do seem to have the many parameters you can adjust in the JPEG
algorithm very well chosen.

Cheers,
David


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
What program is best at JPEG compression? [email protected] Digital Photography 84 August 7th 07 10:20 AM
Controlling compression with (Nikon) digital cameras. [email protected] Advanced Photography 4 January 1st 05 03:11 AM
Controlling compression with (Nikon) digital cameras. [email protected] Digital Photography 4 January 1st 05 03:11 AM
best compression for saving photos in jpeg? Brian Digital Photography 14 December 24th 04 12:59 PM
JPEG compression James Ramaley Digital Photography 14 October 26th 04 01:41 AM


All times are GMT +1. The time now is 10:51 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright 2004-2018 PhotoBanter.com.
The comments are property of their posters.