# Resolution and print size

Discussion in 'Digital Photography' started by Marc Wossner, Jan 23, 2007.

1. ### Marc WossnerGuest

Hi ng,

I´ve a problem understanding digital camera resolution and max print
sizes for files derived by those cameras. I take the Canon EOS-D60 as
an example. The D60 has a pixel size of 7.4 microns, so there are 136
pixels/mm. However, that doesn't mean that the camera will actually
resolve 136 lines per mm. The real useful resolution will be 70-80% of
that, something like 105 lines per mm. Also, this is lines, while film
and lens resolution is always given in line pairs, and it takes two
lines to make a line pair. So the D-60 will actually resolve about 53
line pairs/mm at best. - I know that it makes no sense to compare
resolution in lines/mm as the sensor and 35 mm film are different in
size. Lines/picture height are better. For the D60 this means that
it´s measured resolution limit of 1600 lines/picture height is
equivalent to a 35 mm camera resolution of 1600 / 2 / 24 = 33 line
pairs per mm. - Anyway, if I take those 53 lp/mm into the formula to
calculate system resolution like 1/T = 1/l + 1/f = 1/400+1/53 =
1/0,0214 = 46,8 lp/mm and divide this value by the resolution limit of
the eye for 10 inches (6,88 lp/mm), I reach a max magnification of
x6,8. - I know that this formula gives only a rough approximation. -
The sensor is 22.7 x 15.1 mm, so max print size should be 6 inches
wide. Now I found a value based on experience that says that D60 images
printed at 200 dpi (that´s a full 10x15 inch print) look very good and
sharp. That´s consistent with other statements I found for other
cameras that all give values for max print size that are higher than
can be expected from theoretical resolution alone. It´s quite clear to
me that our perception of sharpness is based on more than resolution
alone, that grain/noise plays an important role as well and that a
camera like the D60 produces images that are virtually noise free. But
as resolution still matters can someone explain to me how those figures
correlate or where I made a mistake in calculating them?

Marc Wossner

Marc Wossner, Jan 23, 2007

2. ### SimonLWGuest

"Marc Wossner" <> wrote in message
news:...
Hi ng,

I´ve a problem understanding digital camera resolution and max print
sizes for files derived by those cameras. I take the Canon EOS-D60 as
an example. The D60 has a pixel size of 7.4 microns, so there are 136
pixels/mm. However, that doesn't mean that the camera will actually
resolve 136 lines per mm. The real useful resolution will be 70-80% of
that, something like 105 lines per mm. Also, this is lines, while film
and lens resolution is always given in line pairs, and it takes two
lines to make a line pair. So the D-60 will actually resolve about 53
line pairs/mm at best. - I know that it makes no sense to compare
resolution in lines/mm as the sensor and 35 mm film are different in
size. Lines/picture height are better. For the D60 this means that
it´s measured resolution limit of 1600 lines/picture height is
equivalent to a 35 mm camera resolution of 1600 / 2 / 24 = 33 line
pairs per mm. - Anyway, if I take those 53 lp/mm into the formula to
calculate system resolution like 1/T = 1/l + 1/f = 1/400+1/53 =
1/0,0214 = 46,8 lp/mm and divide this value by the resolution limit of
the eye for 10 inches (6,88 lp/mm), I reach a max magnification of
x6,8. - I know that this formula gives only a rough approximation. -
The sensor is 22.7 x 15.1 mm, so max print size should be 6 inches
wide. Now I found a value based on experience that says that D60 images
printed at 200 dpi (that´s a full 10x15 inch print) look very good and
sharp. That´s consistent with other statements I found for other
cameras that all give values for max print size that are higher than
can be expected from theoretical resolution alone. It´s quite clear to
me that our perception of sharpness is based on more than resolution
alone, that grain/noise plays an important role as well and that a
camera like the D60 produces images that are virtually noise free. But
as resolution still matters can someone explain to me how those figures
correlate or where I made a mistake in calculating them?

Marc Wossner

Just take the # of pixels on the long side of the image, and divide by 300
dpi for high quality prints, 250dpi for good quality or 200dpi for fair
quality, ect. to get the recommended max print size. Very basic and it has
always worked for me.

When you start splitting hairs with numbers, you have to consider lens
sharpness and contrast, actual resolution of the printer, illumination
levels of print to be viewed and so on.
-S

SimonLW, Jan 23, 2007

3. ### Dr. Joel M. HoffmanGuest

>pairs per mm. - Anyway, if I take those 53 lp/mm into the formula to
>calculate system resolution like 1/T = 1/l + 1/f = 1/400+1/53 =
>1/0,0214 = 46,8 lp/mm and divide this value by the resolution limit of
>the eye for 10 inches (6,88 lp/mm), I reach a max magnification of
>x6,8. - I know that this formula gives only a rough approximation. -
>The sensor is 22.7 x 15.1 mm, so max print size should be 6 inches
>wide. Now I found a value based on experience that says that D60 images
>printed at 200 dpi (that´s a full 10x15 inch print) look very good and
>sharp.

I think a better way of looking at your numbers is this:

Up to 6" wide (or so), you get (almost) no increase in quality from
more pixels, because the increase in resolution is beyond the
resolving power of the human eye.

However, equipment is not perfect, and if any stage of your workflow
introduces fuzziness (which it surely does), you'll find the 6" figure
growing. Suppose, for example (and this is probably true), that you
use a printer that only prints at 200dpi. Then up to 10x15 or so you
get (almost) no increase in quality from more pixels.

It is also true, as you note, that we perceive sharpness based not
only on resolution. This is why sharpening a low resolution image can
make it look sharp, even at the expense of detail. Similarly, I have
seen 3'x4' images printed on canvas from very low resolution images,
and they look great. I suspect this has something to do with the
coarse texture of the canvas, but I don't know for sure.

-Joel

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Dr. Joel M. Hoffman, Jan 23, 2007
4. ### Tzortzakakis DimitriosGuest

? "Marc Wossner" <> ?????? ??? ??????
news:...
Hi ng,

I´ve a problem understanding digital camera resolution and max print
sizes for files derived by those cameras. I take the Canon EOS-D60 as
an example. The D60 has a pixel size of 7.4 microns, so there are 136
pixels/mm. However, that doesn't mean that the camera will actually
resolve 136 lines per mm. The real useful resolution will be 70-80% of
that, something like 105 lines per mm. Also, this is lines, while film
and lens resolution is always given in line pairs, and it takes two
lines to make a line pair. So the D-60 will actually resolve about 53
line pairs/mm at best. - I know that it makes no sense to compare
resolution in lines/mm as the sensor and 35 mm film are different in
size. Lines/picture height are better. For the D60 this means that
it´s measured resolution limit of 1600 lines/picture height is
equivalent to a 35 mm camera resolution of 1600 / 2 / 24 = 33 line
pairs per mm. - Anyway, if I take those 53 lp/mm into the formula to
calculate system resolution like 1/T = 1/l + 1/f = 1/400+1/53 =
1/0,0214 = 46,8 lp/mm and divide this value by the resolution limit of
the eye for 10 inches (6,88 lp/mm), I reach a max magnification of
x6,8. - I know that this formula gives only a rough approximation. -
The sensor is 22.7 x 15.1 mm, so max print size should be 6 inches
wide. Now I found a value based on experience that says that D60 images
printed at 200 dpi (that´s a full 10x15 inch print) look very good and
sharp. That´s consistent with other statements I found for other
cameras that all give values for max print size that are higher than
can be expected from theoretical resolution alone. It´s quite clear to
me that our perception of sharpness is based on more than resolution
alone, that grain/noise plays an important role as well and that a
camera like the D60 produces images that are virtually noise free. But
as resolution still matters can someone explain to me how those figures
correlate or where I made a mistake in calculating them?

Hi,
I printed a full-size A4 (larger than 8X10")with a cheapo Kodak CX 7300 and
a Canon Pixma IP 4300 and looks perfect, much better than any B&W prints I
did in my film era, save colour.(With some german glossy paper, 25 euros for
50 A4 sheets, compu color by Felix Schoeler).Surely you have a better camera
than mine?
Hope this helps,

--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
dimtzort AT otenet DOT gr

Tzortzakakis Dimitrios, Jan 23, 2007
5. ### Paul D. SullivanGuest

> I´ve a problem understanding digital camera resolution and max
> print sizes for files derived by those cameras.

I have historically used the 300 dpi guide, but find that with
digital cameras, I can get pretty good results with a minimum of
about 240 dpi - 250 dpi of resolveable detail, perhaps because
with digital there is no grain or other such distorting factors
to deal with.

This depends on a number of factors, such as the quality of the
camera / ccd / lens, the ISO level of the shot, lighting levels
and type of object being shot.

For outdoor nature shots, I can get away with as low as 200 dpi
and still be somewhat satisfied, but for shots of people,
anything below the 240-250 dpi range and I can start to notice
things.

A good 5mp camera like the Oly C5050 can give you great looking,
300+ dpi prints in 4x6 and 5x7 and still accommodate some
cropping. But for 8x10's, I think 5mp can be stretching it for
non-nature type shots, like portraits, etc.

That's just my personal feeling though. I'm not trying to
indicate that it's right for everybody - it is just what I have
found to be my preferences over the years.

Paul D. Sullivan, Jan 23, 2007
6. ### Marc WossnerGuest

As you all state the common dpi values is the traditional resolution
measure of line pairs per mm or lines per picture with or picture
height not relevant when calculating the resolution of a digital
imaging system? - I still use silver film and try to figure out the
theoretical foundations before I switch to digital.

Marc Wossner

Marc Wossner, Jan 25, 2007
7. ### Gary EickmeierGuest

Marc Wossner wrote:

> As you all state the common dpi values is the traditional resolution
> measure of line pairs per mm or lines per picture with or picture
> height not relevant when calculating the resolution of a digital
> imaging system? - I still use silver film and try to figure out the
> theoretical foundations before I switch to digital.

An interesting aside, Marc - my video projector has a basic 1440 x 1080
pixels resolution, but it displays video at fantastic resolution at a 10
foot wide screen size. To my eye, I can't imagine having any more detail
in some of the images I'm seeing on a good broadcast. My thought is that
all that matters is how big the resultant image is in your eye. If I sat
5 feet away from my screen, it wouldn't fare as well. So I sit about 20
feet back, and it is impressive and amazing.

I have also seen very large paper prints from various digital (and film)
cameras at exhibitions and shows. I guess the proof is in the pudding,
so try various outrageous sizes and see at what point it breaks down.
Probably doable anywhere above 100 DPI.

Gary Eickmeier

Gary Eickmeier, Jan 25, 2007
8. ### David J. LittleboyGuest

"Marc Wossner" <> wrote:
>
> As you all state the common dpi values is the traditional resolution
> measure of line pairs per mm or lines per picture with or picture
> height not relevant when calculating the resolution of a digital
> imaging system? - I still use silver film and try to figure out the
> theoretical foundations before I switch to digital.

Forget the theory: look at the images.

This guy complains about moiré and fine text in street signs getting messed
up, but it sure looks to me that the 5D and 645 (actually, 6x6 cropped to
slightly smaller than 645) are pretty much equivalent for prints 17x26" and
smaller.

http://www.shortwork.net/equip/review-1Ds-SQ-scantech/

David J. Littleboy
Tokyo, Japan

David J. Littleboy, Jan 25, 2007
9. ### Marc WossnerGuest

> On 25 Jan., 15:29, "David J. Littleboy" <> wrote:
> > "Marc Wossner" <> wrote:

>
> > As you all state the common dpi values is the traditional resolution
> > measure of line pairs per mm or lines per picture with or picture
> > height not relevant when calculating the resolution of a digital
> > imaging system? - I still use silver film and try to figure out the
> > theoretical foundations before I switch to digital.

> Forget the theory: look at the images.

Not so easy if something keeps nagging your mind. But I agree with you:
Image quality of the 5D is absolutely stunning.

>
> This guy complains about moiré and fine text in street signs getting messed
> up, but it sure looks to me that the 5D and 645 (actually, 6x6 cropped to
> slightly smaller than 645) are pretty much equivalent for prints 17x26" and
> smaller. http://www.shortwork.net/equip/review-1Ds-SQ-scantech/

So there´s the question again: How can you print that large from the
resolution the 5D gives?
When you calculate 4368 pixels * 0,7 = 3057,6 lines / 2 = 1529 line
pairs / 35,8 mm you reach 42,7 lp/mm.
I don´t know the true resolution of the lens, but as it´s a prime
lens let´s assume 100 lp/mm.
Taking it into account like this 1/T = 1/43 + 1/100 makes it a system
resolution of 30 lp/mm worst case.
The images presented are printed at 17x26" so that´s a magnification
of x18.
Divide the 30 lp/mm by the 2 lp/mm that are necessary for that diagonal
you get a max magnification of x15.
But the guy shows clippings that appear sharp from 10" and for that
distance you need 6,88 lp/mm to have a sharp impression.
Note that those figures are all based on "normal" 20/20 vision or max
resolvable detail of 1 minute of an arc (see Norman Koren´s site for
the calculation: http://www.normankoren.com/Tutorials/MTF.html).
As I know that you are quite knowledgeable from various other threads
David, can you explain me how this is possible, or better, where my
possible misconception is?

Marc

Marc Wossner, Jan 25, 2007
10. ### Paul D. SullivanGuest

I hate math... lol...

> So there´s the question again: How can you print that large
> from the resolution the 5D gives?
> When you calculate 4368 pixels * 0,7 = 3057,6 lines / 2 = 1529
> line pairs / 35,8 mm you reach 42,7 lp/mm.
> I don´t know the true resolution of the lens, but as it´s a
> prime
> lens let´s assume 100 lp/mm.
> Taking it into account like this 1/T = 1/43 + 1/100 makes it a
> system resolution of 30 lp/mm worst case.
> The images presented are printed at 17x26" so that´s a
> magnification of x18.
> Divide the 30 lp/mm by the 2 lp/mm that are necessary for that
> diagonal you get a max magnification of x15.
> But the guy shows clippings that appear sharp from 10" and for
> that distance you need 6,88 lp/mm to have a sharp impression.
> Note that those figures are all based on "normal" 20/20 vision
> or max resolvable detail of 1 minute of an arc (see Norman
> Koren´s site for the calculation:
> http://www.normankoren.com/Tutorials/MTF.html).
> As I know that you are quite knowledgeable from various other
> threads David, can you explain me how this is possible, or
> better, where my possible misconception is?
>
> Marc

Paul D. Sullivan, Jan 25, 2007
11. ### David J. LittleboyGuest

"Marc Wossner" <> wrote:
> On 25 Jan., 15:29, "David J. Littleboy" <> wrote:
> > "Marc Wossner" <> wrote:

>
> This guy complains about moiré and fine text in street signs getting
> messed
> up, but it sure looks to me that the 5D and 645 (actually, 6x6 cropped to
> slightly smaller than 645) are pretty much equivalent for prints 17x26"
> and
> smaller. http://www.shortwork.net/equip/review-1Ds-SQ-scantech/

So there´s the question again: How can you print that large from the
resolution the 5D gives?
<<<<<<<<<<<<<

Well, don't ask me; I think printing 645 larger than 13x19 is nuts. But 35mm
folks make 16x20s all the time. (I saw an exhibit of 20x30s at the Nikon
gallery here that was incredibly soft mush; they looked bad from across the
room.)

Seriously, though, if you have a decent image, the larger you print it, the
better it looks. Even if the result is mush. So no one has ever been unhappy
with a large print they've made from their own images.

>>>>>>>>>>>>>>>

When you calculate 4368 pixels * 0,7 = 3057,6 lines / 2 = 1529 line
pairs / 35,8 mm you reach 42,7 lp/mm.
I don´t know the true resolution of the lens, but as it´s a prime
lens let´s assume 100 lp/mm.
Taking it into account like this 1/T = 1/43 + 1/100 makes it a system
resolution of 30 lp/mm worst case.
<<<<<<<<<<<<<<<<

Let's see. The 5D produces 2912 x 4374 pixels (plus or minus a few depending
on the RAW converter), and digital images tend to have a practical
resolution of about one line pair per 3 pixels. So that's 970 lp/in or 38
lp/mm. OK. Our numbers agree<g>.

In real life, the 5D produces about 240 ppi at 12x18 (1/2" borders on 13x19
paper). The prints look gorgeous. That's a 12x enlargement with 3 lp/mm
resolution. That's pretty cool, because film look really really bad at a 12x
enlargement. Either grainy or mushy or both.

>>>>>>>>>>>>>>>>

The images presented are printed at 17x26" so that´s a magnification
of x18.
Divide the 30 lp/mm by the 2 lp/mm that are necessary for that diagonal
you get a max magnification of x15.
But the guy shows clippings that appear sharp from 10" and for that
distance you need 6,88 lp/mm to have a sharp impression.
<<<<<<<<<<<<<<<<<

My theory on what's going on here is that your "you need 6,88 lp/mm to have
a sharp impression" is due to misinformation from the dizzy Leica folks.

What they do is shoot high contrast (1:1000) test charts and assume that
their real life images achieve similar levels of detail capture; they think
that tests with strobe illuminated charts with the camera bolted to granite
test bench somehow relates to handheld street shooting. My experience
shooting film (and the data sheets from the mfrs) is that you see nothing of
the sort in real life images _other than street signs_. Film types (and
I've made this mistake myself) will look at a street sign image and think
how cool it is that their camera resolves it, while failing to notice that
the textures at that enlargement not only aren't captured, but are
completely swamped by the grain noise.

>>>>>>>>>>>>>>>>

Note that those figures are all based on "normal" 20/20 vision or max
resolvable detail of 1 minute of an arc (see Norman Koren´s site for
the calculation: http://www.normankoren.com/Tutorials/MTF.html).
As I know that you are quite knowledgeable from various other threads
David, can you explain me how this is possible, or better, where my
possible misconception is?
<<<<<<<<<<<<<<<<

He's looking at film images that are grossly soft as well. I've printed a
lot of test images at that magnification from film, and they're mush.

David J. Littleboy
Tokyo, Japan

David J. Littleboy, Jan 26, 2007
12. ### Paul D. SullivanGuest

> In real life, the 5D produces about 240 ppi at 12x18 (1/2"
> borders on 13x19 paper). The prints look gorgeous. That's a
> 12x enlargement with 3 lp/mm resolution. That's pretty cool,
> because film look really really bad at a 12x enlargement.
> Either grainy or mushy or both.

That is one of the great things about digital - no grain.

My 5mp Oly C5050 does 8x10 at 240 ppi and it looks at least as
good as 8x10's that I have taken and had printed with my 35mm
film camera. Sometimes it is obviously clearer even if the level
of detail is not as great overall.

Paul D. Sullivan, Jan 26, 2007
13. ### Marc WossnerGuest

On 26 Jan., 01:42, "David J. Littleboy" <> wrote:
> "Marc Wossner" <> wrote:
> > On 25 Jan., 15:29, "David J. Littleboy" <> wrote:
> > > "Marc Wossner" <> wrote:

>
> > This guy complains about moiré and fine text in street signs getting
> > messed
> > up, but it sure looks to me that the 5D and 645 (actually, 6x6 cropped to
> > slightly smaller than 645) are pretty much equivalent for prints 17x26"
> > and
> > smaller. http://www.shortwork.net/equip/review-1Ds-SQ-scantech/So there´s the question again: How can you print that large from the

> resolution the 5D gives?
> <<<<<<<<<<<<<
>
> Well, don't ask me; I think printing 645 larger than 13x19 is nuts. But 35mm
> folks make 16x20s all the time. (I saw an exhibit of 20x30s at the Nikon
> gallery here that was incredibly soft mush; they looked bad from across the
> room.)
>
> Seriously, though, if you have a decent image, the larger you print it, the
> better it looks. Even if the result is mush. So no one has ever been unhappy
> with a large print they've made from their own images.
>
> When you calculate 4368 pixels * 0,7 = 3057,6 lines / 2 = 1529 line
> pairs / 35,8 mm you reach 42,7 lp/mm.
> I don´t know the true resolution of the lens, but as it´s a prime
> lens let´s assume 100 lp/mm.
> Taking it into account like this 1/T = 1/43 + 1/100 makes it a system
> resolution of 30 lp/mm worst case.
> <<<<<<<<<<<<<<<<
>
> Let's see. The 5D produces 2912 x 4374 pixels (plus or minus a few depending
> on the RAW converter), and digital images tend to have a practical
> resolution of about one line pair per 3 pixels. So that's 970 lp/in or 38
> lp/mm. OK. Our numbers agree<g>.
>
> In real life, the 5D produces about 240 ppi at 12x18 (1/2" borders on 13x19
> paper). The prints look gorgeous. That's a 12x enlargement with 3 lp/mm
> resolution. That's pretty cool, because film look really really bad at a 12x
> enlargement. Either grainy or mushy or both.
>
> The images presented are printed at 17x26" so that´s a magnification
> of x18.
> Divide the 30 lp/mm by the 2 lp/mm that are necessary for that diagonal
> you get a max magnification of x15.
> But the guy shows clippings that appear sharp from 10" and for that
> distance you need 6,88 lp/mm to have a sharp impression.
> <<<<<<<<<<<<<<<<<
>
> My theory on what's going on here is that your "you need 6,88 lp/mm to have
> a sharp impression" is due to misinformation from the dizzy Leica folks.

> What they do is shoot high contrast (1:1000) test charts and assume that
> their real life images achieve similar levels of detail capture; they think
> that tests with strobe illuminated charts with the camera bolted to granite
> test bench somehow relates to handheld street shooting. My experience
> shooting film (and the data sheets from the mfrs) is that you see nothing of
> the sort in real life images _other than street signs_. Film types (and
> I've made this mistake myself) will look at a street sign image and think
> how cool it is that their camera resolves it, while failing to notice that
> the textures at that enlargement not only aren't captured, but are
> completely swamped by the grain noise.
>
> Note that those figures are all based on "normal" 20/20 vision or max
> resolvable detail of 1 minute of an arc (see Norman Koren´s site for
> the calculation:http://www.normankoren.com/Tutorials/MTF.html).
> As I know that you are quite knowledgeable from various other threads
> David, can you explain me how this is possible, or better, where my
> possible misconception is?
> <<<<<<<<<<<<<<<<
>
> He's looking at film images that are grossly soft as well. I've printed a
> lot of test images at that magnification from film, and they're mush.

No. I do analog photography for a long time and started studying the
perception side to make better use of the medium. That´s where all I
know is derived from. The 6,88 lp/mm are calculated using only figures
of our visual system. Koren´s site explains this and all the
informations are backed up by a lot of scientifc research. 1 minute of
an arc *is* the resolution limit of the *average* human and the 6,88 is
based on that. But you can also reach it from another side:

cycles/degree = 600/Snellen denominator = 600/20 = 30 cycles/degree
cycles/degree * (180/pi) * (1/distance in mm) = 30 * (180/pi) * (1/250
mm) = 6,87 lp/mm

As stated this is an average value and a lot of people can see much
better, in the range of 60 cycles/degree.
That´s what I know and where it comes from. It holds true in analog
photography and that´s why I don´t understand what´s going on in the
digital case.

Marc

Marc Wossner, Jan 26, 2007
14. ### Guest

Forgive my selective editing, David, but in these three bits, I think
you summed it up well.

On Jan 26, 10:42 am, "David J. Littleboy" <> wrote:
> Seriously, though, if you have a decent image, the larger you print it, the
> better it looks. Even if the result is mush...

> My theory on what's going on here is that your "you need 6,88 lp/mm to have
> a sharp impression" is due to misinformation...

> What they do is shoot high contrast (1:1000) test charts and assume that
> their real life images achieve similar levels of detail capture...

Exactly. The 300 ppi thing (which is derived from the 6.88) is almost
useless, imo, as a guide to enlargability, unless you are only
enlarging resolution test charts. If the image content is any of the
following, then you can decrease that figure, sometimes dramatically:

- close up macros without fine detail (eg flower macros, not insects
with lots of tiny hairs..)
- very tightly cropped portraits (because getting too close to a face
feels uncomfortable to the viewer)
- soft focus portraits (obviously)

- a landscape (is that grass/foliage/pine needles.. or mush(â„¢David)?)
- cityscape (is that blurry bit my house, or why can't I read that
little sign?),
- beachscape (is that girl way back there topless?)
- or a large group portrait (is that Uncle Ed or Aunt Martha, 3rd row,
10th from the end?)

I proved this to myself long ago when I first tested out the much
maligned Sony DSCF828 (which does produce very nice and quite sharp 8Mp
images.) I blew a series of images up to 13" x 19" prints (ie about
190 ppi), including portraits like this one:

http://www.marktphoto.com/portrait/slides/happiness_is.jpg
(sorry, slightly oversharpened - you'll have to trust me that the
original is nailed!)

and also landscapes and other images that invited close inspection,
like this:

http://www.marktphoto.com/marina_details.jpg

The portraits looked stunning, and yet the detailed shots like the
second example looked mediocre. You would have sworn they were taken
on two different cameras. But on close inspection, you could see that
the portrait was indeed exactly as sharp as the other - it was a
combination of the way you viewed the images (the portrait 'made' you
want to view it at about 18" at which point you could see all the
*useful* detail, right down to the detail in the irises and
eyelashes.., but the landscape invited much closer inspection and you
could more easily see the very slight pixellation, even at the same
viewing distance). There's a lot of factors in this, eg diagonal
jaggies are much more likely to show up in boat rigging than eyes...
and of course how well you post process, what method you interpolate
with, etc...

Anyway, if you add it all up, your brain will tell you how sharp the
print is, but it is very likely lying..!

Just use the 300/200/100 thing as a vague guide and experiment..

, Jan 26, 2007
15. ### Marc WossnerGuest

After digging deeper into this I found a way to explain the facts that
contradict each other at first glance.
The following quote from an old thread lead me the way: "It´s not the
resolution of the image on the retina that makes the difference, it´s
the contrast of the relatively well resolved information." What
matters here is the subjective quality factor (sqf) and the fact that
the better contrast that most digital cameras reproduce at the spatial
frequencys between 5 and 10 cycles/degree, which are most important
for perceived sharpness, allows for larger prints than the resolution
numbers alone predict. The following three websites give further
information:

http://www.bobatkins.com/photography/technical/mtf/mtf4.html
http://www.imatest.com/docs/sqf.html
http://luminous-landscape.com/forum/lofiversion/index.php/t11480.html

Marc

Marc Wossner, Jan 28, 2007