The digital zoom myth busted

The digital zoom test.

The equipment included a Nikon Coolpix 5000 camera with Firmware 1.7. I
used a triopd. I set the camera to manual mode, and made all the exposures
on the same setting. I used "fine" full resolution .jpg files, because that
is the setting I most frequently use. I set the camera to 80mm mode (full
optical telephoto) and made several exposures. Then I used the 4x digital
zoom and made several exposures.

After downloading the files to the PC, I used Photoshop 6 to resample the
optical zoom to 4x as large. That's from 2560x1920 to 10240x7680 with the
bicubic setting. I cropped the large file to approximately the size of the
small file. At this point I have two images on the monitor. They have about
the same number of pixels and about the same field of view.

Here are the two images, side by side (digital zoom on the right) at 100%:

http://www.2fiddles.com/photos/UnalteredSampleCopy.tif (273k)

After applying levels of 36, 0.81, and 178, I arrived at this:

http://www.2fiddles.com/photos/levelsCopy.tif (351k)

I provide the first file in case anyone would like to perform experiments
on the unaltered files. Although I call the optical zoom image
"unaltered," it really has been altered. I used photoshop to resample it.
For those who might like to try other resampling software, there is the
original section of the optical zoom:

http://www.2fiddles.com/photos/OpticalSample.tif (51k)

To my eyes, the digital zoom looks better. There is better gradiation in
the colors. In particular, I'm comparing the green leaf and the orange leaf
in the lower right hand quadrant. In exchange, the resampled optical zoom
seems to have a tiny bit more shadow detail, as seen in the pine needles in
the upper left quadrant.

The one thing they are not, is the same, which is the myth. I performed
this test to confirm observations I made under less controlled
circumstances, where I though the digital zoom rendered tones smoother, but
the exposures were different, which prevented a good comparison.

Bob

PS the samples are all lwz compression PC byte order Photoshop tifs. The
quicktime plugin does a good job of opening them, but they won't open in at
least some browsers in "standard trim."

--
Delete the inverse SPAM to reply

bob wrote:
The digital zoom test.

My understanding is that the camera will crop and enlarge the area under
digital zoom *before* conversion to jpg, which would explain differences
in picture quality.

Try the experiment again with the camera set to produce RAW or TIF or BMP
files.

Kibo informs me that "Jacobe Hazzard"
stated that:

bob wrote:
The digital zoom test.

My understanding is that the camera will crop and enlarge the area under
digital zoom *before* conversion to jpg, which would explain differences
in picture quality.

That would be my explanation too.

Try the experiment again with the camera set to produce RAW or TIF or BMP
files.

Betcha digital-zoom isn't available in RAW mode.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

wrote in newsj9un0t0dch7ejorid8kimh4dg1siug2io@
4ax.com:

Kibo informs me that "Jacobe Hazzard"
stated that:

bob wrote:
The digital zoom test.

snip
Betcha digital-zoom isn't available in RAW mode.

Reminds me of a joke about a heavy metal group band member that was having
an animated argument with his manager:

"So let me see if I got this straight. We got live chickens squawking on
the stage, and we kill the chickens an axe... Then we chop up one of the
speakers, and we totally trash all the guitars and the drum set, all in
order to get the most out of the concert, and you decided to record it
digitally to get better sound ???"

--
Lasse Vågsæther Karlsen
http://www.vkarlsen.no/

PGP KeyID: 0x0270466B

Kibo informs me that "Lasse Vågsæther Karlsen"
stated that:

wrote in newsj9un0t0dch7ejorid8kimh4dg1siug2io@
Betcha digital-zoom isn't available in RAW mode.

Reminds me of a joke about a heavy metal group band member that was having
an animated argument with his manager:

"So let me see if I got this straight. We got live chickens squawking on
the stage, and we kill the chickens an axe... Then we chop up one of the
speakers, and we totally trash all the guitars and the drum set, all in
order to get the most out of the concert, and you decided to record it
digitally to get better sound ???"

Heh. Good summary.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

Jacobe Hazzard wrote:
bob wrote:
The digital zoom test.

My understanding is that the camera will crop and enlarge the area
under digital zoom *before* conversion to jpg, which would explain
differences in picture quality.

Try the experiment again with the camera set to produce RAW or TIF or
BMP files.

I agree - although my argument /for/ using digital zoom in the past has
been based on the premise that (providing you stick to 2:1 zoom - perhaps
4:1 but I've not tested that) the interpolated image in the camera will
suffer less from the JPEG compression than the full resolution image.

One added factor in Bob's tests is that he is also "testing" the
interpolation algorithms used on Photoshop 6.

Thanks for sharing your results, Bob.

David

"David J Taylor"
wrote in
:

Jacobe Hazzard wrote:
bob wrote:
The digital zoom test.

My understanding is that the camera will crop and enlarge the area
under digital zoom *before* conversion to jpg, which would explain
differences in picture quality.

Try the experiment again with the camera set to produce RAW or TIF or
BMP files.

I agree - although my argument /for/ using digital zoom in the past
has been based on the premise that (providing you stick to 2:1 zoom -
perhaps 4:1 but I've not tested that) the interpolated image in the
camera will suffer less from the JPEG compression than the full
resolution image.

One added factor in Bob's tests is that he is also "testing" the
interpolation algorithms used on Photoshop 6.

Thanks for sharing your results, Bob.


It was an interesting experiment, and you're welcome.

I did consider testing RAW mode, but I do not frequently use RAW mode. I
wanted to find out how to maximize the quality of my system, given how I
typically use it.

RAW mode takes much longer to write files, they are much larger, and
given typical lighting, don't seem to produce better prints. With my
camera. TIF files (on my camera) have all the disadvantages of RAW, only
more so, with none of the advantages.

I got the camera for it's wide angle abilities and I will continue to use
it that way. If I found I frequently needed longer focal lengths, I would
consider the teleconverter, but for now, if I know I'm going to be
cropping before printing, there seems to be an advantage to using the
digital zoom, especially where the subject is characterized by smooth
tones.

Bob

--
Delete the inverse SPAM to reply

wrote:
Kibo informs me that "Jacobe Hazzard"
stated that:


bob wrote:

The digital zoom test.

My understanding is that the camera will crop and enlarge the area under
digital zoom *before* conversion to jpg, which would explain differences
in picture quality.


That would be my explanation too.


Try the experiment again with the camera set to produce RAW or TIF or BMP
files.


Betcha digital-zoom isn't available in RAW mode.


Many of he new cameras use complex algorithms for making digital zoom
look better. These are usually referred to as 'enhanced digital zoom'
in the specs. Results vary, but some shots do look better than a simple
digital zoom.

On Wed, 27 Oct 2004 10:43:35 -0500, Jim Townsend
wrote:

bob wrote:

To my eyes, the digital zoom looks better. There is better gradiation in
the colors. In particular, I'm comparing the green leaf and the orange leaf
in the lower right hand quadrant. In exchange, the resampled optical zoom
seems to have a tiny bit more shadow detail, as seen in the pine needles in
the upper left quadrant.

The one thing they are not, is the same, which is the myth. I performed
this test to confirm observations I made under less controlled
circumstances, where I though the digital zoom rendered tones smoother, but
the exposures were different, which prevented a good comparison.

Digitally zoomed images have much less detail than those taken in regular
mode.. You have far less pixels to work with. All the processing in the
world won't get you detail that isn't there.

Digital zoom still isn't the same as optical zoom. No matter what you
do to your digitally zoomed picture, they will never have the detail of
the non zoomed ones.

He isn't claiming that. Obviously optical zoom is going to be better -
always. He is simply comparing in-camera digital-zoom with a digital
zoom that is done afterwards in software by cropping a section from a
non-digital-zoomed image.

Because you couldn't match what the camera did using Photoshop doesn't mean
it can't be done. I find it hard to believe that there is absolutely no
way for any editing software to match what Nikon's can do in its firmware..

Nikon's firmware has more data at it's disposal - it has access to the
12bit raw image which is quite obviously better than attempting to do
the same from an already compressed 8-bit jpeg outside the camera.
Now, if he were playing with NEF (RAW) or TIFF instead, the comparison
may show neither method is superior.

Here is a test: take a 1/4 section of any picture and compare it's
histogram to that of the whole picture, they are different right? And
that's part of the problem with an after-the-jpeg digital-zoom, the
jpeg was optimized based on the whole scene's levels, not just on the
section you want to zoom to.

Now, I must be alone here, but I think the image on the left
(photoshop's resize) is better than the digital-zoom - much less
artifacts, and the color difference isn't that big.

It is interesting however that the CP 5000 has such an effective resampling
algorithm..

I don't think it's anything special.

--
Owamanga!

Jim Townsend wrote:
[]
It is interesting however that the CP 5000 has such an effective
resampling algorithm..

Nikon seem to have very good firmware - their JPEGs seem to be able to
retain picture information in smaller files than other cameras need. I
suspect the parameters for the compression have been carefully chosen to
match the lens and sensor characteristics.

Careful attention to detail.

Cheers,
David