HELP: PS 6.01 72 VS 300 DPI Dilemma

RPK said:

Just to clarify my original posting.

Per the EXIF data on a raw and unedited JPG straight out of the
camera, the DPI setting show as 300 DPI. Only after "saving as"
through Photoshop does it drop down to 72 DPI. No actions, crops or
edits were done, just simply saving it as a different file.

I'm very lost ...

Either the camera is mis-reporting the DPI as 300 or Photoshop is
doing something that I don't know about.

When saving the "edited" .JPG, I always choose the lowest
compression / highest file size method. This leads to another
question.

If my original .JPG is say 1.MB and I save in PS with a compression
setting of 12 (highest I believe) what's happening to inflate the
file upwards to 2.0MB? I am not gaining data, I believe it's just
compressed less. With this in mind, should I always save at "12"
and have a larger file than the original or go for the normal
compression setting?

Now on to saving as a .TIFF from a .JPEG, what is the point there.
If it's already compressed once, didn't I loose the data? Will I
have any additional gain by using the .TIFF format. Bear in mind,
the file was a .JPG in the first place.

Click to expand...

When you resave in .JPG, which is not highly recommended because you can lose details, Photoshop is probably resampling all the data of the original, which is 300 DPI and resampling it to 72 DPI. The best way is to never touch the originals. Open the originals and the use "Save As" to save as another file, thus leaving your original with all its data untouched. Otherwise try saving as .JPG, but make sure the "resampling" is off.

The other way is to save it in .TIFF, which will result in a larger file, but with retain all 300 DPI of data. TIFF files are the standard format that professionals use to save their image files.

Tsan, thank you! I've got it and appreciate your opening my eyes.

You say that .TIFF is the industry standard for professionals. With that in mind, do I have an advantage of saving my editied .JPG as a .TIFF? I know that .JPG will throw away a little data every time so I guess .TIFF would be the best route. BUT if the original is .JPG, what are the advantages?

No no no no no..... Let's start from the beginning...

Let's say you have an image file from your camera. The camera shoots at a resolution of 640x480 pixels. The color depth is 24 bits/pixel. So this would produce a

640x480=307200 x 24 bits = 7372800 bits / 8 = 921600 bytes
921600 bytes / 1024000 = .9 Mb

So the native file size of a 24 bit 640x480 pixel file is .9 Mb

Now, your camera offers several methods to conserve space so you can shoot and store more pictures. Typically it uses JPEG lossy compression and lets you choose between several different quality settings. So if you use jpeg compression at say 4:1, your .9 Mb file will be compressed to .22 Mb or 225 Kb.

Then when you transfer this jpeg image file to your computer and open it up with Photoshop for editing, photoshop will uncompress the file to display a 24 bit 640x480 pixel file. The .9Mb filesize will reappear in the status window.

There's a simple algebraic formula that can be used to calculate the resolution, etc.

Pixel dimension divided by resolution = document dimension

640 pixels / 300 pixels/inch = 2.13 inches
480 pixels / 300 pixels/inch = 1.60 inches

If I change one of these variables, like the resolution, then several things can happen. If for example, the resolution is changed to 72 pixels/inch (Photoshop's default) and the image stays the same (we still have the same total number of pixels) then either the pixel dimension decreases or the document size increases. Normally, Photoshop will adjust the document dimension.

640 pixels / 72 pixels/inch = 8.88 inches
480 pixels / 72 pixels/inch = 6.66 inches

We still have the exact same amount of colored dots, they are just spread over a larger area. The quality of your image has not decreased.

Now, when you save this file in Photoshop to a jpg file (agian using jpeg compression) with a quality set to "12" (which for this example we'll say does 2:1 compression), your new file would be about .45 Mb.

What does this do to your image quality (independent of any processing like sharpening, etc. which you may have used to improve the photo)?

When your camera originally compressed the image, some data was lost. That's why it is referred to as lossy compression. It trys to remove dots that you would not normally notice so the image quality appears close to the original image. When you open the camera's jpeg in Photoshop, it is de-compressed to the original pixel count. New data is added to replace the dots removed by the camera's jpeg compression. The software decodes by guessing the best color pixel for the replacement (I'm really over-simplifying this, but...) Then, when you save it as a jpeg again, other dots (possible some of the same ones as before) are removed. The quality setting is used to determine how much will actually get removed. Compressing over and over will degrade the image quality. With every generation of compression, more data is potentially lost. So I wouldn't recommend opening your original image in photoshop just to adjust the resolution so it says 300 DPI.

I usually open my images and then SAVE-AS the new jpeg to a different file so I can always retain the original camera file as-is.

Tsan said:

RPK said:

Just to clarify my original posting.

Per the EXIF data on a raw and unedited JPG straight out of the
camera, the DPI setting show as 300 DPI. Only after "saving as"
through Photoshop does it drop down to 72 DPI. No actions, crops or
edits were done, just simply saving it as a different file.

I'm very lost ...

Either the camera is mis-reporting the DPI as 300 or Photoshop is
doing something that I don't know about.

When saving the "edited" .JPG, I always choose the lowest
compression / highest file size method. This leads to another
question.

If my original .JPG is say 1.MB and I save in PS with a compression
setting of 12 (highest I believe) what's happening to inflate the
file upwards to 2.0MB? I am not gaining data, I believe it's just
compressed less. With this in mind, should I always save at "12"
and have a larger file than the original or go for the normal
compression setting?

Now on to saving as a .TIFF from a .JPEG, what is the point there.
If it's already compressed once, didn't I loose the data? Will I
have any additional gain by using the .TIFF format. Bear in mind,
the file was a .JPG in the first place.

Click to expand...

When you resave in .JPG, which is not highly recommended because
you can lose details, Photoshop is probably resampling all the data
of the original, which is 300 DPI and resampling it to 72 DPI. The
best way is to never touch the originals. Open the originals and
the use "Save As" to save as another file, thus leaving your
original with all its data untouched. Otherwise try saving as .JPG,
but make sure the "resampling" is off.

The other way is to save it in .TIFF, which will result in a larger
file, but with retain all 300 DPI of data. TIFF files are the
standard format that professionals use to save their image files.

Click to expand...

There's no advantage to the TIFF unless you plan to edit multiple generations of the original image. Using TIFF avoids losing any data due to compression. However, if you work from a copy of the original jpg and store the original jpeg in a safe place, you will be fine. You'll have a smaller file and the original data - best of both worlds.

RPK said:

Tsan, thank you! I've got it and appreciate your opening my eyes.

You say that .TIFF is the industry standard for professionals. With
that in mind, do I have an advantage of saving my editied .JPG as a
.TIFF? I know that .JPG will throw away a little data every time
so I guess .TIFF would be the best route. BUT if the original is
.JPG, what are the advantages?

Click to expand...

RPK said:

Tsan, thank you! I've got it and appreciate your opening my eyes.

You say that .TIFF is the industry standard for professionals. With
that in mind, do I have an advantage of saving my editied .JPG as a
.TIFF? I know that .JPG will throw away a little data every time
so I guess .TIFF would be the best route. BUT if the original is
.JPG, what are the advantages?

Click to expand...

As long as you keep that original .JPG file unedited, it will be fine. It saves space.

Some people make a .TIFF save of their originals and use the .TIFF for editing. From there you can created resized images for web use and then save to .JPG. If you need to use your original again, open it and save it to another .TIFF file and edit for whatever use you need.

Good luck,
Tsan

RPK said:

Ok, I know this issue has already been hashed here but I am still
at a loss of why things are happening.

Scenario:
1). Open 1MB JPEG in Photoshop 6.0 / 300 DPI / shot in CoolPix 995
"fine" mode / 2560 x 1920

Click to expand...

DPI and PPI explain different concepts. DOTS per inch have to do with printing processes. PIXELS per inch have to do with how many pixels are crushed into an inch of reproduction. Your computer screen is probably about 90 PPI but many are as low-res as 72 PPI. Your print will want to see about 180 PPI for great looking images.

Photoshop had to peg it somewhere, and when it re-saves things, unless you intercede to tell it different, it uses 72 PPI.

With an image open, full size, you can change the PPI number and watch the size of image change. Make sure that "Resample Image" is not checked.

That 300 PPI (or marked at DPI) idea is bogus. The file may show it as data, but when you think about trying to reproduce a pixel accurately at 300 of them per inch, the meaningful difference that pixel contributes to the image gets totally lost.

Even an Epson printer at 2880 X 720 dpi will only have 9 pixels wide, by two pixels tall, of potential color spots to define that 300 dpi original camera pixel detail. To reproduce that camera pixel accurately, it will need to have a chunk of paper surface that can accomodate 256 levels of Cyan, Magenta, Yellow and blacK ink. That means the equivalent of a 32 X 8 dot patch of print surface (or 16 x 16). Anything less is a statistical compromise.

RPK said:

2). Apply auto-levels and unsharp-mask
3). Save file, JPEG at it's 10 setting (high quality), no resize /
2560 x 1920

When checking the EXIF info, the file now is 72 DPI but still at
2560 x 1920. What's happening here. Is Photoshop making a mistake
in the DPI? Even more odd, if I change the size to 300 DPI within
PS, the file print size goes smaller instead of larger.

If the dimensions are the same 2560 x 1920, does it matter what the
DPI is? I'm left wondering why PS took it to 72 DPI from 300 DPI
with no loss of file size.

HELP!

Click to expand...

You can ignore the 72 or 300 when Resample Image is disabled. Pay attention to the Document Size numbers in inches or cm first, then look at the pixels/inch (cm) number to see how detailed things are going to be on the final print.

National Geographic Magazine, for instance, uses a 175 dot line screen to reproduce color images inside the magazine. Covers are 150 dpi. Rules of photographic thumb.

-iNova

RPK said:

Ok, I know this issue has already been hashed here but I am still
at a loss of why things are happening.

Scenario:
1). Open 1MB JPEG in Photoshop 6.0 / 300 DPI / shot in CoolPix 995
"fine" mode / 2560 x 1920
2). Apply auto-levels and unsharp-mask
3). Save file, JPEG at it's 10 setting (high quality), no resize /
2560 x 1920

When checking the EXIF info, the file now is 72 DPI but still at
2560 x 1920. What's happening here. Is Photoshop making a mistake
in the DPI? Even more odd, if I change the size to 300 DPI within
PS, the file print size goes smaller instead of larger.

If the dimensions are the same 2560 x 1920, does it matter what the
DPI is? I'm left wondering why PS took it to 72 DPI from 300 DPI
with no loss of file size.

HELP!

Click to expand...

Hi

As I understand it, if the image is 2560 x 1920, then that IS the size of the image.

DPI only affects the PRINTED size that can be attained from the given image size in pixels.

i.e. If you set DPI to 100 you would get a 25.6 x 19.2 inch print, if you set DPI to 200 you would get a 12.8 x 9.6 inch print ect...

No matter what you set the DPI to, your image will always be 2560 x 1920 pixels on screen, the size it displays at 100% zoom being determined by the screen resoloution you have set. The file size does not change if you alter the DPI figure alone.

Hope this helps.

You use several terms. A 175 dot line screen is analog & produces much more resulotion than 150 dpi since the dots are of varying sizes. I followed you reasoning until this paragraph. What are you trying to say since a dot line screen does not equate to DPI or PPI. Thanks.

Peter iNova56624 said:

National Geographic Magazine, for instance, uses a 175 dot line
screen to reproduce color images inside the magazine. Covers are
150 dpi. Rules of photographic thumb.

-iNova

Click to expand...

--Bill Liggett

I think you mean that National Geographic Covers are 150 line screen. A 150 line photographic screen is analog producing dots of varying sizes making it much more precise than 150 dots per inch. A dot line screen is different than DPI. Your paragraph is inconsistent.

Peter iNova said:

National Geographic Magazine, for instance, uses a 175 dot line
screen to reproduce color images inside the magazine. Covers are
150 dpi. Rules of photographic thumb.

Click to expand...

--Bill Liggett

Debbie et. al.:

First: Photoshop DOES NOTHING with your DPI from your original JPG-image!!! Most of the digtal cameras save their JPGs with 72 or 96 DPI, not more or less. Period! If you open your downloaded image (e.g. with Nikon-View 4) you can see the resolution in the image description file delivered with the image, if you have turned the txt-file option on (what I did for several other reasons).

The DPI information of your image is more or less unimportant. It has historical reasons why cameras are saving with 72/96 DPI. The resampling of the image (should be the last step of a digital processing in whatever program) is important for the further use (e.g web applications, ink jet printers, laser prints etc.) to adjust the image size to the REAL physical resolution of your output device (72 DPI for screens, ~ 200 DPI for most of the common used ink jet printers, 400/600 ... for laser printers and even more).

So just refer to the manual of your output device to set the proper final resolution (200 for ink jets, 300/600 for laser printers) and get the maximum allowable image size you can display or print (see some of the post above).

After resizing it make no sense to print a image bigger than calculated by Photoshop (or whatever). The result will be a pixelized (or blurry/unsharp) picture. If you want to crop a part of your image after resizing, take care of the remaining REAL image dimension you can print, it's smaller, of course!

You can refer to my homepage (sorry, folks, it's in German), where you can fnd a table with the maximum allowable print sizes. It was cited from my users manual of my Nikon CP995, so you can also refer to that.

http://home.t-online.de/home/c.kleimeier/html/grundlagen.htm

All the best from Germany

Christoph

Debbie said:

RPK said:

Ok, I know this issue has already been hashed here but I am still
at a loss of why things are happening.

Scenario:
1). Open 1MB JPEG in Photoshop 6.0 / 300 DPI / shot in CoolPix 995
"fine" mode / 2560 x 1920
2). Apply auto-levels and unsharp-mask
3). Save file, JPEG at it's 10 setting (high quality), no resize /
2560 x 1920

When checking the EXIF info, the file now is 72 DPI but still at
2560 x 1920. What's happening here. Is Photoshop making a mistake
in the DPI? Even more odd, if I change the size to 300 DPI within
PS, the file print size goes smaller instead of larger.

If the dimensions are the same 2560 x 1920, does it matter what the
DPI is? I'm left wondering why PS took it to 72 DPI from 300 DPI
with no loss of file size.

HELP!

Click to expand...

--
Debbie

Click to expand...

Christoph Kleimeier said:

Debbie et. al.:

First: Photoshop DOES NOTHING with your DPI from your original
JPG-image!!! Most of the digtal cameras save their JPGs with 72 or
96 DPI, not more or less. Period! If you open your downloaded image
(e.g. with Nikon-View 4) you can see the resolution in the image
description file delivered with the image, if you have turned the
txt-file option on (what I did for several other reasons).

The DPI information of your image is more or less unimportant. It
has historical reasons why cameras are saving with 72/96 DPI. The
resampling of the image (should be the last step of a digital
processing in whatever program) is important for the further use
(e.g web applications, ink jet printers, laser prints etc.) to
adjust the image size to the REAL physical resolution of your
output device (72 DPI for screens, ~ 200 DPI for most of the common
used ink jet printers, 400/600 ... for laser printers and even
more).

So just refer to the manual of your output device to set the proper
final resolution (200 for ink jets, 300/600 for laser printers) and
get the maximum allowable image size you can display or print (see
some of the post above).

After resizing it make no sense to print a image bigger than
calculated by Photoshop (or whatever). The result will be a
pixelized (or blurry/unsharp) picture. If you want to crop a part
of your image after resizing, take care of the remaining REAL image
dimension you can print, it's smaller, of course!

You can refer to my homepage (sorry, folks, it's in German), where
you can fnd a table with the maximum allowable print sizes. It was
cited from my users manual of my Nikon CP995, so you can also refer
to that.

http://home.t-online.de/home/c.kleimeier/html/grundlagen.htm

All the best from Germany

Christoph

Click to expand...

Cristoph,

Your handling of English makes me very envious as an American who speaks(?) it and a little southwestern Spanish. Guten tag.

Paul Linder

Christoph Kleimeier said:

Debbie said:

RPK said:

Ok, I know this issue has already been hashed here but I am still
at a loss of why things are happening.

Scenario:
1). Open 1MB JPEG in Photoshop 6.0 / 300 DPI / shot in CoolPix 995
"fine" mode / 2560 x 1920
2). Apply auto-levels and unsharp-mask
3). Save file, JPEG at it's 10 setting (high quality), no resize /
2560 x 1920

When checking the EXIF info, the file now is 72 DPI but still at
2560 x 1920. What's happening here. Is Photoshop making a mistake
in the DPI? Even more odd, if I change the size to 300 DPI within
PS, the file print size goes smaller instead of larger.

If the dimensions are the same 2560 x 1920, does it matter what the
DPI is? I'm left wondering why PS took it to 72 DPI from 300 DPI
with no loss of file size.

HELP!

Click to expand...

--
Debbie

Click to expand...

Click to expand...

Christoph Kleimeier said:

Debbie et. al.:

First: Photoshop DOES NOTHING with your DPI from your original
JPG-image!!! Most of the digtal cameras save their JPGs with 72 or
96 DPI, not more or less. Period!

Click to expand...

I tried to tell 'em the same thing a week ago, but everybody had other complex twists to such a simple fact.

Sorry, Bruce,that I have repeated your comment, but I've tried to follow up all the threads going with this (now somewhat annoying) discussion. I'm certainly NOT an professional photographer as you are (what I've found in your personal profike of this forum), so your statement makes me proud -what means that I now know that I have understand the facts behind digital photography. Thanks for your reply!

One thing that I want to follow personally as good as I can: Read, read, read, whatever it was and try to understand....

All the best from rainy Stade/Germany

Christoph

Bruce M. said:

Christoph Kleimeier said:

Debbie et. al.:

First: Photoshop DOES NOTHING with your DPI from your original
JPG-image!!! Most of the digtal cameras save their JPGs with 72 or
96 DPI, not more or less. Period!

Click to expand...

I tried to tell 'em the same thing a week ago, but everybody had
other complex twists to such a simple fact.

Click to expand...

Paul,

thanks for your kind words! May be the reason is, that I work for an American chemical company (Dow Chemical) for roughly 11 years and I have to speak and write English/American as good as I can. As long as i understand what my partner/colleague is telling me and vice versa, it's OK with me, regardless how good or bad I wrote or speak.

Nevertheless, this dicussion has to be stopped, it' (my personal oppinon) is worthless know...

Thanks again and all the best

Christoph
from Himmelpforten (near Hamburg) Germany

P.S.: Your name sound pretty German?!

Paul Linder said:

Christoph Kleimeier said:

Debbie et. al.:

First: Photoshop DOES NOTHING with your DPI from your original
JPG-image!!! Most of the digtal cameras save their JPGs with 72 or
96 DPI, not more or less. Period! If you open your downloaded image
(e.g. with Nikon-View 4) you can see the resolution in the image
description file delivered with the image, if you have turned the
txt-file option on (what I did for several other reasons).

The DPI information of your image is more or less unimportant. It
has historical reasons why cameras are saving with 72/96 DPI. The
resampling of the image (should be the last step of a digital
processing in whatever program) is important for the further use
(e.g web applications, ink jet printers, laser prints etc.) to
adjust the image size to the REAL physical resolution of your
output device (72 DPI for screens, ~ 200 DPI for most of the common
used ink jet printers, 400/600 ... for laser printers and even
more).

So just refer to the manual of your output device to set the proper
final resolution (200 for ink jets, 300/600 for laser printers) and
get the maximum allowable image size you can display or print (see
some of the post above).

After resizing it make no sense to print a image bigger than
calculated by Photoshop (or whatever). The result will be a
pixelized (or blurry/unsharp) picture. If you want to crop a part
of your image after resizing, take care of the remaining REAL image
dimension you can print, it's smaller, of course!

You can refer to my homepage (sorry, folks, it's in German), where
you can fnd a table with the maximum allowable print sizes. It was
cited from my users manual of my Nikon CP995, so you can also refer
to that.

http://home.t-online.de/home/c.kleimeier/html/grundlagen.htm

All the best from Germany

Christoph

Click to expand...

Cristoph,
Your handling of English makes me very envious as an American who
speaks(?) it and a little southwestern Spanish. Guten tag.

Paul Linder

Paul Linder said:

Debbie said:

RPK said:

Ok, I know this issue has already been hashed here but I am still
at a loss of why things are happening.

Scenario:
1). Open 1MB JPEG in Photoshop 6.0 / 300 DPI / shot in CoolPix 995
"fine" mode / 2560 x 1920
2). Apply auto-levels and unsharp-mask
3). Save file, JPEG at it's 10 setting (high quality), no resize /
2560 x 1920

When checking the EXIF info, the file now is 72 DPI but still at
2560 x 1920. What's happening here. Is Photoshop making a mistake
in the DPI? Even more odd, if I change the size to 300 DPI within
PS, the file print size goes smaller instead of larger.

If the dimensions are the same 2560 x 1920, does it matter what the
DPI is? I'm left wondering why PS took it to 72 DPI from 300 DPI
with no loss of file size.

HELP!

Click to expand...

--
Debbie

Click to expand...

Click to expand...

Click to expand...