Photo compression

[Guest]

When I download my pictures from my camara they are jpeg. My question is:
When I print the pictures are they still in the compressed stage or in the
uncompressed? Thanks Mack

 

[Bumbrlik]

The jpeg pictures are stored in a specific way (what you call a compressed
format) - it is a bunch of coefficient coming from a discrete cosine
transformation. Don't worry about it, the format is irrelevant when you view
the picture or print it. Any software that can handle jpeg format will know
what to do.

 

[Jim]

When I download my pictures from my camara they are jpeg. My question is:
When I print the pictures are they still in the compressed stage or in the
uncompressed? Thanks Mack

Uncompressed. JPEGs must be uncompressed before anything can be done with
them.
Jim

 

[yves alarie]

The answer is yes, in the sense that your computer cannot send more
information to the printer than what is contained in the jpeg file. So your
prints are of a quality dependent upon the level of compression you selected
in your camera.
A jpeg file is a "compressed" file in the sense that the information
captured by the sensor of your digital camera is stored in the jpeg format
(or TIF or RAW format if your camera can do this, these are so to speak
uncompressed formats and the file size will be much larger).
Your camera uses this compression (instead of RAW or TIF) to save space on
your memory card and if you look in your camera manual you will see that you
can use different level of compression. Something like "ultra fine", "fine"
etc. The higher the compression level you select in your camera, the smaller
the file will be and the lower the quality of the print will be.
When you send a jpeg file to your printer, the information available is only
what is in the jpeg file (according to the level of compression you selected
in your camera), nothing more and nothing less. There is no "decompression",
there is only a translation (the printer driver does this) of the
information in the jpeg file to your printer.
So, the print will be better if you select the lowest compression level
available in your camera.

You can take a look at this site about jpeg compression and how it affects
the image and print.
http://en.wikipedia.org/wiki/JPEG

 

[Guest]

I have a 5 meg camara and set at it's lowest (or best picture) compression.
When I download to my pc it compresses it to the jpeg settings. I can change
to tiff after it is on my pc. Say a 2 megabyte picture becomes a 14 megabyte
picture. Is this what I need to do before I print them out. Thanks, Mack

 

[Yves Alarie]

NO.
The damage is done. When you save as JPEG in your camera it stays as JPEG
and is copied to your computer, obviously, as JPEG. Your computer does not
compress the file to JPEG, it is already a JPEG file on your camera memory
card.
YES you can convert it to TIF. However, you will gain nothing by doing this
and sending this converted JPEG file to TIF to your printer over the
original JPEG.
If you want a TIF file, you need to save it as TIF in your camera (if your
camera can do this) and you pay a big price: much larger file size.
Having said this, it now depends on what you want to do with the file and
how you want to edit this JPEG file.
When you open a JPEG file for editing in a particular editing software, you
do your editing and you "Save as" to save your editing. There will be "some"
degradation to the new file. So, you don't want to edit and "Save as" 5 or
10 etc. times adding new edits to this original file (note here that when
you open a JPEG to view it and you then just close it there is absolutely no
degradation, this comes only when you Save As).
In this editing case, it is fine to convert your JPEG to TIF. Then you edit
the TIF file as many times as you want and Save As as many times as you
want, no degradation with Save As of a TIF file.
Don't let me scare you about "degradation".
You have a 5 MP camera and you use the lowest compression JPEG. This is
extremely good. Using Save As a few times as you edit the file will make no
visible difference.
It also depends what you use to edit. For example, if you use editing
software like Adobe Photoshop Element 3 or Microsoft Digital Image Pro, when
you Save As your edits, you are given the option of Save as in formats such
as .psd or .png. You can Save As as many times as you want in these formats,
no degradation. You simply use this until you complete your editing and then
you Save As JPEG when you are ready to print. This saves you from having to
convert the JPEG to TIF.

The issue of JPEG vs TIF is certainly worth knowing about when using a
digital camera. Below is a little exercise. Nothing like doing it yourself
to find out exactly what is going on and then deciding how you will proceed
with your settings.

Using TIF over JPEG is best


This used to be correct, in the days of poor resolution digital cameras and
scanners. Things have changed dramatically and unless you want to print very
large (by large I mean more than 12 x 18) from a pro shop there is
absolutely no advantage to save tif files over jpg for printing.

The first point is, every time you "Save as" a jpg there is a little loss
and artifacts introduced, so if you edit a picture and you Save as many
time, there is some degradation with each Save as, but not with Save if you
use Save to save your changes as you are editing(even if you don't do
anything to the picture and you Save as, just to change the name of the
file,
it is the Save as that is the problem). So if you plan to edit the file many
times, keep it in tif until done and then save it as jpg. Since you can
always saved it back as tif for further editing, no problem.
The second point is, can you see the difference? Only you can tell, no
amount of info will convince you. So you do the experiment yourself. It has
been done many times. Here is how to do it.
Take one of your jpg file, right click on it and click on Copy. Hold the
Ctrl key down and press the letter V. This will make a new file in your
folder "Copy of filename.jpg" (note there is no degradation when you do
this,
since you don't open the file and Save as, you only copied it). Now.
1. Open this file in your photo editor and Save as. Give it the name Copy of
filename 1.jpg
2. Open Copy of filename 1.jpg, Save as and change 1 to 2 in the file name.
3. Continue doing this until you Save as this file 15 times.
Then you can start opening them and look at them on your screen, when do you
begin to see degradation? Can't see it yet, keep going to 25 Save As. At one
point you will see the degradation.
But the real test is not seeing on your screen, you screen magnifies
everything and we don't trust you (well, no insult here!) since you know the
number you are looking
at.
Now, print number 1, 3, 9, 15 and 25. Print as large as your printer can
print.
Don't look at the print too closely, just place a little number in pencil on
the back of them. Then, give them to somebody and ask them to place them on
a table in a random order. Can you pick No.1? If you do, try again the
next day. Did you get it again? If you can pick No 1 consistently, then it
does make a difference. If not, no more to argue about.
Then you can ask your tif using friends to pick the print they think is the
best.
You may be surprised!

If your camera can save directly in tif, you can also make a direct
comparison. Set the camera on a tripod, take the same scene ( take 4 or 5)
in tif and jepg and then print. Can you consistently pick the tif over jepg.

If you do, then shoot in tif when you have an important picture, otherwise
use jpeg.
Give us your results a few weeks from now, if you wish. We do not always
have the same objectives when taking photos.

 

[Yves]

When I started my answer and said "the damage is done" I should have
explained what the "damage" is.
What I mean by damage is simply that if you save as RAW or TIF in your
camera you get the best possible. Saving as JPEG is a step below in quality,
your camera does the compression to JPEG format to save space on your memory
card. This compression is, so to speak, "damage". So converting your JPEG to
TIF is not going to help, except to edit and Save As many times as I
explained.
But, how much "damage" saving in JPEG? With your camera at 5 MP and using
the lowest compression I doubt that you can see any such damage.
Sorry about not adding this. I did not mean to scare you by "the damage is
done".

 

[Guest]

Thanks for replying. I understand all that you said, but what I don't
understand is this: a picture that is say 2 megabytes, when I convert to
tiff it becomes say 14 megabytes. Where does the extra megabytes come from?
Thanks, Mack

 

[Yves Alarie]

Good question!
Not so easy to answer.
Let me try to answer it. The answer below is not exactly "technically"
correct but it will give you an idea of what is happening.
Say you take a picture of the letter I, the letter is black and the
background is white paper.
A black object on a white background is very little information. If I save
this as a TIF file all the white pixels and all the black pixels are saved.
Big file.
If I save it as a JPEG, the algorithm in your camera looks at all the white
and says, in essence, why save all this. It is all white (or close enough)
so don't save all the white pixels. It then sees the black I, no big deal,
it is all black so why save all the pixels. Your computer software will read
the JPEG file and in essence, reconstruct (not decompress) the picture file
for you to see it and print it. This "black and white" example is probably
the best I can give you, because there is a very high contrast between black
and white and when JPEG algorithm is used instead of TIF the file will be
very very small, but regardless of the scene you photograph, the TIF file
will always be the same size. However, in doing so (JPEG compression) the
details in the white area will be lost (not everything is absolutely white)
and the edges between black and white will not be absolutely sharp (what is
called JPEG jaggies).
Now you have this JPEG file on your computer and you convert it to TIFF. It
makes a huge file because it tries to reconstructs every pixel as if the
picture was saved as TIF, instead of saying forget about all white and all
black as JPEG does. However, this reconstruction is worthless (unless you
want to edit and save as and prevent deterioration with Save as as you edit
with a JPEG), the JPEGs jaggies are there and all the white is white and all
the black is black.
If instead, you saved the picture in your camera as a TIF file, not all the
white is white, there is a gradation and not all the black is black, there
is a gradation and the edges between the black I and the white background is
saved properly. A lot more information saved in a TIF file and therefore a
larger file, such information is "discarded" when saving as JPEG. So
converting a JPEG file to TIF with your computer cannot create an original
TIF file taken by your camera. Thus my opening statement "the damage is
done"!
You can see this easily with your camera. Set it for the highest compression
JPEG (lowest picture quality) and take a picture of a big I letter on a
piece of white paper. Then convert it to TIF. See if you can see any
improvement when converting to TIF. Then take the same picture in TIF (if
your camera can do this) and compare. Huge difference. Easy to see. But then
take the same picture with the lowest compression and compare to TIF (if
your camera can do so) and with your camera at 5 MP and lowest compression
setting you probably will not be able to see the difference between the two,
low compression JPEG and no compression TIF.

Hope this helps, as I said, the above is not absolutely technically correct,
but it tells you that converting a low (or high) compression JPEG into a TIF
in your computer will not improve the quality of your prints, it will simply
make a much larger file, nothing more and nothing less. Thus the saying "the
damage is done" when you save in your camera with JPEG.
If you want a TIF file, set your camera to take one. You can't create an
original TIF file by converting a JPEG file to a TIF file in your computer
and with your camera at 5 MP, I really don't see why you would want to save
as TIF unless you are a pro photographer or you want really large prints
done at a pro lab.

 

[John Inzer]

Thanks for replying. I understand all that you said, but
what I don't understand is this: a picture that is say 2
megabytes, when I convert to tiff it becomes say 14
megabytes. Where does the extra megabytes come from?
Thanks, Mack

=====================================
The file size is radically different because of the
..jpg compression.

If you open the saved 2 MB .jpg in a program
that can assess file size (IrfanView for example).
You will see that the 2 MB .jpg is 14 MB when
uncompressed.

In IrfanView you can see this info at...Image /
Information / Current Memory Size.


--

John Inzer
Picture It! MVP
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Picture It! Support Center
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[Guest]

Thanks for all your answers. I understand how it works now. HP tells me
that I can convert and technically I can, it justs doesn't do any good or
improve the picture. The 8x10's that I print out now couldn't get any
better. I just wanted to know how it worked. Thanks for all your time and
the answers. Mack

 

[Yves Alarie]

Great.
Nothing like understanding how things work.
Now, happy shooting with your camera!

 

[Yves Alarie]

Hi John.
Quite true. But the 14 MB is memory size, not file size.
So if now you save this file as TIF, the file becomes 14 MB instead of 2 MB,
but there is no improvement if you print this same file as TIF (14 MB) or
JPEG (2 MB).

 

[John Inzer]

Hi John.
Quite true. But the 14 MB is memory size, not file size.
So if now you save this file as TIF, the file becomes 14
MB instead of 2 MB, but there is no improvement if you
print this same file as TIF (14 MB) or JPEG (2 MB).

============================
Memory size / file size...semantics...
The files are virtually the same aside
from the compression. And of course...
..jpg is lossy and .tif is lossless.

--

John Inzer
Picture It! MVP
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Picture It! Support Center
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[yves alarie]

I look at this differently.
The file size of the JPEG is 2 MB, but when you open it to see it on your
screen and to print it, the memory needed to display it and print it is 14
MB. This is the memory size and converting the file to TIF would result in a
file size of 14 MB. But the quality would still be JPEG, not an original
TIF.