Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Computing > Digital Photography > File Size vs. Printed Photo Size

Reply
Thread Tools

File Size vs. Printed Photo Size

 
 
All Things Mopar
Guest
Posts: n/a
 
      03-21-2005
Roger N. Clark Commented courteously...

> Notes on the Resolution and Other Details of the Human

Eye
> http://www.clarkvision.com/imagedetail/eye-

resolution.html
>
> Here is a test where people can tell the difference

between
> 300 and 600 ppi prints:
> http://www.clarkvision.com/imagedetail/printer-ppi


Thanks for the links. Interesting reading. Viewing
distance and quite a few other factors enter into this
issue, of course.

Dr. Kris Zaklika of Corel's Paint Shop Pro division
(formerly, Jasc), has published a pretty convincing
treatise that suggests that the human eye.

My personal opinion at this point is that the OP may have
been more interested in the practical minimums for PPI
rather than perhaps what might be termed the theoretical
minimums. But, that's just my opinion.

Here's what Dr. Zaklika had to say:

The way you eye works is roughly like this. There are
light sensitive cells in the back of your eye which have a
particular size and spacing. Your eye can't resolve two
objects that, when projected on the back of your eye, fall
on just a single light sensor. How big an object will be
when it is projected onto the back of the eye depends on
the angle it subtends at the eye.

Ignoring failures of the eye lens and the need to wear
corrective glasses, there is a minimal subtended angle for
an object to be resolved. Objects that subtend a smaller
angle are perceived as one indistinct object. It's this
angle that is critical. What this angle means is that
small details can be seen when they are close to your eye
but only large details can be seen when they are far from
your eye. Stand next to a dog and you can see each hair of
its fur but look at a dog 100 meters away and you cannot
see the hairs (even though you can see the fur in some
general way). All this means that the largest image you
can print with acceptable quality depends on how far you
will be from this image when you look at it.

The rough rule of thumb is that at normal viewing distance
of around 24 inches, an object subtending the minimal
angle at the eye is about 1/200th of an inch. This means
you need 200
pixels per inch to show all the detail. If you place more
pixels in every inch your eye will simply be unable to see
them or, more accurately, will be unable to discern the
detail they represent. Some really pedantic people examine
their images very closely and claim that they need 300
pixels to capture all the detail. Other people believe 150
pixels per inch give them an acceptable picture. I would
use 150 pixels per inch as a lower limit for images seen
at normal distances.

This would mean that your 3072 by 2048 image could be
printed at 3072/150 by 2048/150 inches or about 20.5 x
13.6 inches. However, you have to consider this. The
bigger you print your image, the less likely it is that
you will be very close to it when looking at it. This is
because you won't be able to see all of the image when you
are too close. Therefore, if you need a large image to
hang on a wall that will typically be viewed from a
distance of 6 feet and not 2 feet, you could print it at
50 to 100 pixels per inch (instead of 150 to 300). This
would allow you to make a picture as big as 3072/50 by
2048/50 inches or about 61 x 41 inches. Of course, if you
stood close to such a print, you would see the distinct
pixels. This, then, is why the answer to your question
depends on the circumstances and on what you need. The
attached diagram is an attempt to explain some of what I
have said in a visual way.


--
ATM, aka Jerry
 
Reply With Quote
 
 
 
 
Bubbabob
Guest
Posts: n/a
 
      03-21-2005
If you want to find out what the appropriate rez for your printer is, go to
this site, download the PDF files and print them. It will be obvious. A
little empirical science beats a whole lot of anecdotal rot.

<http://www.inkjetart.com/tips/ppi/>
 
Reply With Quote
 
 
 
 
Roger N. Clark (change username to rnclark)
Guest
Posts: n/a
 
      03-22-2005
All Things Mopar wrote:

> Dr. Kris Zaklika of Corel's Paint Shop Pro division
> (formerly, Jasc), has published a pretty convincing
> treatise that suggests that the human eye.
>
> My personal opinion at this point is that the OP may have
> been more interested in the practical minimums for PPI
> rather than perhaps what might be termed the theoretical
> minimums. But, that's just my opinion.
>
> Here's what Dr. Zaklika had to say:
>
> The way you eye works is roughly like this. There are
> light sensitive cells in the back of your eye which have a
> particular size and spacing. Your eye can't resolve two
> objects that, when projected on the back of your eye, fall
> on just a single light sensor. How big an object will be
> when it is projected onto the back of the eye depends on
> the angle it subtends at the eye.
>
> Ignoring failures of the eye lens and the need to wear
> corrective glasses, there is a minimal subtended angle for
> an object to be resolved. Objects that subtend a smaller
> angle are perceived as one indistinct object. It's this
> angle that is critical. What this angle means is that
> small details can be seen when they are close to your eye
> but only large details can be seen when they are far from
> your eye. Stand next to a dog and you can see each hair of
> its fur but look at a dog 100 meters away and you cannot
> see the hairs (even though you can see the fur in some
> general way). All this means that the largest image you
> can print with acceptable quality depends on how far you
> will be from this image when you look at it.
>
> The rough rule of thumb is that at normal viewing distance
> of around 24 inches, an object subtending the minimal
> angle at the eye is about 1/200th of an inch. This means
> you need 200
> pixels per inch to show all the detail.


This is pretty close to the actual data, but he misses a critical
factor. His number of 1/200 inch at 24 inches is 0.43 arc-minutes,
close to the published visual acuity of 1.7, which
means resolving objects 0.6 arc-minutes separation. But this
number refers to RESOLVING two objects as separate. You need to
pixels to resolve something (there must be a pixel in between
the two spots/lines). Thus his numbers should be doubled.
If one takes the published visual acuity data for the human eye,
then 0.6 arc minutes at 24 inches is about 1/240. But needing
two pixels, that means in the print you need 480 pixels per inch.

> If you place more
> pixels in every inch your eye will simply be unable to see
> them or, more accurately, will be unable to discern the
> detail they represent. Some really pedantic people examine
> their images very closely and claim that they need 300
> pixels to capture all the detail. Other people believe 150
> pixels per inch give them an acceptable picture. I would
> use 150 pixels per inch as a lower limit for images seen
> at normal distances.


The above numbers are not in conflict; meaning the lower
limit, though subjective, is generally accepted as about
150 pixels per inch. However, this doesn't mean you can't
make larger prints from interpolated images. I made a
stunning (if I do say so myself) 16 x 18 inch prints from
a 3 megapixel original (6.3 MP camera, cropped). In original
pixels that is about 114 dpi in original pixels per inch
interpolated up to 305 ppi for printing on a Lightjet.
The image won in the Natures Best International photo contest:
http://www.clarkvision.com/features/....best.win.2004

Subject and image impact is more important than pixels per inch!

> This would mean that your 3072 by 2048 image could be
> printed at 3072/150 by 2048/150 inches or about 20.5 x
> 13.6 inches. However, you have to consider this. The
> bigger you print your image, the less likely it is that
> you will be very close to it when looking at it. This is
> because you won't be able to see all of the image when you
> are too close. Therefore, if you need a large image to
> hang on a wall that will typically be viewed from a
> distance of 6 feet and not 2 feet, you could print it at
> 50 to 100 pixels per inch (instead of 150 to 300). This
> would allow you to make a picture as big as 3072/50 by
> 2048/50 inches or about 61 x 41 inches. Of course, if you
> stood close to such a print, you would see the distinct
> pixels. This, then, is why the answer to your question
> depends on the circumstances and on what you need. The
> attached diagram is an attempt to explain some of what I
> have said in a visual way.


BUT a truly spectacular image, when printed large draws people
in close. In a large print, say 40 x 50 inches, watch people's
mouths drop as they approach a really sharp print, especially
when it is sharp up close, 10 inches away. You only get that
with large format cameras. 40 inches * 300ppi x 50 inches *
300 ppi = 180 Megapixels. Large format 4x5 Fujichrome Velvia
delivers such images (and more).

Roger
Photos, digital info at: http://www.clarkvision.com
 
Reply With Quote
 
Stephen Poley
Guest
Posts: n/a
 
      03-22-2005
On Mon, 21 Mar 2005 08:09:59 -0000, Bubbabob
<rnorton@_remove_this_thuntek.net> wrote:

>Stephen Poley <(E-Mail Removed)> wrote:
>
>> On Mon, 21 Mar 2005 03:14:40 GMT, http://www.velocityreviews.com/forums/(E-Mail Removed) (Dr. Joel M. Hoffman)
>> wrote:
>>
>>>>I finally bought the Lumix FZ20k. It includes a variety of photo size
>>>>options, from TIF to JPG, from 2560 to 640, from find to now to fine.
>>>>Are there general recommendations about file size vs. the type of
>>>>photos one might want to print? For example, if I will never exceed
>>>>5x7, can I reduce from, say, 2560 to 1280, and not worry about it?
>>>
>>>As a general rule, you want 300dpi in a final print. (400dpi looks
>>>better, but beyond that you don't get much improvement.

>>
>> I don't believe that you (or anyone else) can tell the difference
>> between a 300 dpi print and a 400 dpi print.

>
>If you have fine vertical lines or parallel diagonal lines, you'll see
>the difference. You need to pick a print resolution that has a
>relationship to the actual pitch of the nozzles. For all Epson and Canon
>printers it's 360 ppi. 720 works but there's not much point in it. Other
>values will cause moires.


OK, we may be talking at cross-purposes. If we're talking about the
actual printing process, I agree with your comments. There can be
reasons for having a printing pitch finer than the resolution of the
image being printed. But the OP was talking about photo image size.

It's also true that my statement required some qualifications - but I
decided to get a reaction first and then add them.

See my other post.

--
Stephen Poley
 
Reply With Quote
 
Stephen Poley
Guest
Posts: n/a
 
      03-22-2005
On Mon, 21 Mar 2005 07:30:41 -0700, "Roger N. Clark (change username to
rnclark)" <(E-Mail Removed)> wrote:

>Bubbabob wrote:
>> Stephen Poley <(E-Mail Removed)> wrote:
>>
>>
>>>On Mon, 21 Mar 2005 03:14:40 GMT, (E-Mail Removed) (Dr. Joel M. Hoffman)
>>>wrote:
>>>
>>>
>>>>>I finally bought the Lumix FZ20k. It includes a variety of photo size
>>>>>options, from TIF to JPG, from 2560 to 640, from find to now to fine.
>>>>>Are there general recommendations about file size vs. the type of
>>>>>photos one might want to print? For example, if I will never exceed
>>>>>5x7, can I reduce from, say, 2560 to 1280, and not worry about it?
>>>>
>>>>As a general rule, you want 300dpi in a final print. (400dpi looks
>>>>better, but beyond that you don't get much improvement.
>>>
>>>I don't believe that you (or anyone else) can tell the difference
>>>between a 300 dpi print and a 400 dpi print.

>>

>The human eye has incredible resolution. Most current
>printer are limited to good quality, but the printer is the
>limit, not the eye.


Having made a sweeping statement, I guess I'd better add the
qualifications.

Firstly: I have frequently seen it said that the major commercial labs
do no better than 300 pixels per inch, and I have seen no evidence to
the contrary. And based on the evidence of what I have seen friends and
acquaintances producing, one isn't going to improve on the quality of
commercial labs with the run-of-the-mill printers that most people have.
One is going to have to expend considerable money and effort. In that
context the bald statement to an apparent newbie that 400 dpi (I gather
pixels per inch was intended) looks better than 300, with no further
qualification, is simply silly. Hence my rather sweeping reaction.

Having said that, I remain rather skeptical about the claims of the
megapixelphiles as far as real photographic situations are concerned.
Yes, in testcard-like situations there may well be a visible difference.
But no-one I know wants to look at photographs of testcards. Yes, if one
is photographing fine black and white print, there may be a difference.
I use a scanner/photocopier, not a camera. The line resolution tests you
refer to apply only to pure black / pure white line pairs. Replace them
with medium brown / medium green line pairs and you won't get even
approximately the same results.

In any case, for 80% of the camera users I have met (note that I didn't
use the word photographer) striving for anything over 300 ppi would
certainly be a complete waste of time.

--
Stephen Poley
 
Reply With Quote
 
Stephen Poley
Guest
Posts: n/a
 
      03-22-2005
On 21 Mar 2005 22:04:23 -0800, (E-Mail Removed) wrote:

>>... I find it comic that people discussing the latest and
>> greatest technology persist in using inches.

>
>We use inches because the *entire print industry* thinks in, and uses,
>inches. I live in a metric country but we still use dpi, ppi, and inch
>measurements for paper - because that's what they are still cut to, and
>that is the worldwide standard.


Rubbish. The pack of paper lying in front of me now announces its
dimensions as 210x297mm. Nothing about inches. My local processing
service offers 13cm photos, 20cm photos etc. Nothing about inches.

>If you want to use pixels per cm, go
>ahead, but don't expect many to follow or recognise your numbers.
>
>And I'm afraid if you can't see the difference between 300 dpi and 100
>dpi ...


Who said anything about 100 dpi? I didn't.

--
Stephen Poley
 
Reply With Quote
 
Bubbabob
Guest
Posts: n/a
 
      03-23-2005
Stephen Poley <(E-Mail Removed)> wrote:

> Firstly: I have frequently seen it said that the major commercial labs
> do no better than 300 pixels per inch, and I have seen no evidence to
> the contrary.


Noritsu 3101 processors, pretty much the top of the line, use 320 ppi.
Fuji Frontiers operate at 400 ppi.
 
Reply With Quote
 
Bubbabob
Guest
Posts: n/a
 
      03-23-2005
Stephen Poley <(E-Mail Removed)> wrote:

> Rubbish. The pack of paper lying in front of me now announces its
> dimensions as 210x297mm. Nothing about inches. My local processing
> service offers 13cm photos, 20cm photos etc. Nothing about inches.
>


The accomodation for metric papers is in the printer driver software. The
ink nozzles are laid out in inches.
 
Reply With Quote
 
Confused
Guest
Posts: n/a
 
      03-23-2005
Bubbabob <rnorton@_remove_this_thuntek.net> wrote:

> Stephen Poley <(E-Mail Removed)> wrote:
>
> > Rubbish. The pack of paper lying in front of me now announces its
> > dimensions as 210x297mm. Nothing about inches. My local processing
> > service offers 13cm photos, 20cm photos etc. Nothing about inches.

>
> The accomodation for metric papers is in the printer
> driver software. The ink nozzles are laid out in inches.


I don't know about ink nozzles, but when this Californian wrote
printer and plotter drivers for Epson and Lotus back in the dot-matrix
and ribbon days I don't remember having to do any metric conversions.
Internationalization other than accommodating Japan and the USA was
considered, yet. The important criteria was microcomputer based
systems that worked 100% of the time... until the paper jammed.

Technology was changing so fast very few people could keep up, let
alone worry about silly things like which measurement system was used.
The bulk of the inventions and programs came from the USA and there
was no need to change "metrics".

That was then, this is now, and a lot has changed. Maybe we need an
entirely new measurement system so everyone has to change and the "It
must be metric!" camp won't be so uppity. ;^)

Jeff
 
Reply With Quote
 
chrlz@go.com
Guest
Posts: n/a
 
      03-24-2005
Yes, indeed A4 is a metric size of 210 x 297. Nice round figures..

My point was, visit ANY website, talk to any printer or photographer or
publisher, and ask them to think in pixels per cm. You will get blank
stares. Can you point us to any sites that discuss these issues and
use dpc and/or ppc?


And no, I see that you *didn't* say that you couldn't spot the
difference between 100 and 300 dpi - on re-reading your post, you said
this:

> I can't see the difference between 120 pixels per cm
> (300 pixels per inch) and 100 without a magnifying glass.


I apologise - because I am *so* used to talking in dpi and ppi, I read
that as 100 *ppi*. You didn't label it, nor did you put the conversion
in, as you did for the first figure. And it didn't occur to me that
you would be making a point of not being able to tell the difference
when you increased linear resolution by only 20%...

 
Reply With Quote
 
 
 
Reply

Thread Tools

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

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Relive Those Photo Memories With a Printed PHOTO BOOK or CALENDAR! photo Digital Photography 0 12-09-2006 05:22 PM
Re: File Size vs. Printed Photo Size chrlz@go.com Digital Photography 7 03-24-2005 12:22 AM
Canon A70 - getting date printed on photo Mike Digital Photography 7 11-24-2004 01:23 PM
Where to get Photo books printed? C.S. Digital Photography 2 06-17-2004 08:00 AM
Printed photo life length... PR Digital Photography 10 09-17-2003 09:01 PM



Advertisments