Reducing picture size with same quality.
 

I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are
reduced to about 500KB with software such as Photoshop. When I take
small pictures with the camera the quality/definition is very good. I
don't want to take two shots of everything just to be able to get
small pictures for emailing. Why cant large quality pictures be
reduced to smaller ones - with the same definition?
Peter

Reducing picture size with same quality.
 

On Fri, 23 Mar 2012 14:46:51 +1100, Peter Jason wrote:

I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are
reduced to about 500KB with software such as Photoshop. When I take
small pictures with the camera the quality/definition is very good. I
don't want to take two shots of everything just to be able to get
small pictures for emailing. Why cant large quality pictures be
reduced to smaller ones - with the same definition?

Peter,

I would be asking this question in one of the Photoshop newsgroups, of
which I see about 10 on my news server.

Reducing picture size with same quality.
 

Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are
reduced to about 500KB with software such as Photoshop. When I take
small pictures with the camera the quality/definition is very good. I
don't want to take two shots of everything just to be able to get
small pictures for emailing. Why cant large quality pictures be
reduced to smaller ones - with the same definition?
Peter

There are a couple ways to shrink picture size.

1) Resolution change. You can use "scale image"
in your image editor, and change the locked together
"X resolution" and "Y resolution" settings from say
1200 DPI to 600 DPI. That cuts the number of pixels by
a factor of 4.

2) You can use a lossless compression format. I think GIF is
lossless, but it only supports pictures with 256 colors.
There are other examples here of lossless methods. You
might get a factor of 3 using a lossless method. Using
(1) and (2), we can get close to a factor of 12.

http://en.wikipedia.org/wiki/Image_compression

3) Once you move to a lossy compression method, then you're
in control of the picture quality versus size tradeoff.

http://en.wikipedia.org/wiki/Jpeg

If you look at the "Jpeg tombstone" image further down
that page, and look at Q=10, you get a compression of 46:1 .
Which is a significant improvement.

There are other methods of compression. The JPEG article
mentions the algorithm isn't applied all that intelligently,
and there are some options for further improvement. But then,
the person receiving the picture, might not have a decoder for it.

Another form of compression, involves fractals.

http://en.wikipedia.org/wiki/Fractal_compression

That article says fractal compression starts to win, at
compression ratios higher than 50:1. And that's why I
picked the Q=10 picture in particular, from the JPEG article.
If the picture quality at Q=10 is good enough, you probably
can't do much better with the fractal method. But if the
quality is unacceptable, then a fractal method taking a
long time to compress, may achieve a more pleasing result.

Most good lossy compression methods (100:1 compression), will tend
to have a weakness for certain kinds of content. They may do
better with "natural images", than with artificially generated
images (like a cartoon with solid colors). A cartoon sees
excellent compression with GIF, probably higher than the
factor of three that I quoted above.

The best way to learn about this stuff, is to play with it.

Paul

Reducing picture size with same quality.
 

On 23/03/2012 2:46 PM, Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are
reduced to about 500KB with software such as Photoshop. When I take
small pictures with the camera the quality/definition is very good. I
don't want to take two shots of everything just to be able to get
small pictures for emailing. Why cant large quality pictures be
reduced to smaller ones - with the same definition?
Peter


http://answers.microsoft.com/en-us/w...9-ad9acd370b9b

Reducing picture size with same quality.
 

On 03/22/12 23:46, Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are
reduced to about 500KB with software such as Photoshop. When I take
small pictures with the camera the quality/definition is very good. I
don't want to take two shots of everything just to be able to get
small pictures for emailing. Why cant large quality pictures be
reduced to smaller ones - with the same definition?
Peter

Because, when you transfer one gallon of beer, into an one pint glass,
some of the beer will spill out.
And that's against the Law in most Countries,
(spilling beer, that's it).....

Reducing picture size with same quality.
 

In message , Peter Jason
writes:
I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are
reduced to about 500KB with software such as Photoshop. When I take
small pictures with the camera the quality/definition is very good. I
don't want to take two shots of everything just to be able to get
small pictures for emailing. Why cant large quality pictures be
reduced to smaller ones - with the same definition?
Peter

My first reaction was to say they can't, but then I got to wondering
what _method_ you are using in Photoshop (and, for that matter, the
camera) to achieve smaller sizes.

If you're reducing the image size in pixels, you obviously will lose
definition.

If you're reducing it by image compression, you won't lose definition,
on the whole - you'll just risk getting artefacts visible in some
places.

If the "smaller" pictures your camera takes have quality/definition
that's "very good", why do you take the larger ones at all (i. e. why
not leave the camera set to "smaller")? [I'm curious to know whether
it's a pixel-size or a "quality" setting thing in the camera.
--
J. P. Gilliver. UMRA: 1960/1985 MB++G.5AL-IS-P--Ch++(p)Ar@T0H+Sh0!:`)DNAf

....Every morning is the dawn of a new error...

Reducing picture size with same quality.
 

On 3/22/12 9:46 PM, Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are
reduced to about 500KB with software such as Photoshop. When I take
small pictures with the camera the quality/definition is very good. I
don't want to take two shots of everything just to be able to get
small pictures for emailing. Why cant large quality pictures be
reduced to smaller ones - with the same definition?
Peter

One question no one asked, what makes you say you lose definition?

--
Ken

Mac OS X 10.6.8
Firefox 10.0.2
Thunderbird 10.0.2
LibreOffice 3.5.0 rc3

Reducing picture size with same quality.
 

On 22/03/2012 11:46 PM, Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are
reduced to about 500KB with software such as Photoshop. When I take
small pictures with the camera the quality/definition is very good. I
don't want to take two shots of everything just to be able to get
small pictures for emailing. Why cant large quality pictures be
reduced to smaller ones - with the same definition?
Peter

Reducing image size (eg from 4000x3000 pixels to 1200x800 pixels) will
"lose definition" as you cal it. There is no way around that. Reason: a
detail that was shown with a 6x6 pixel square in the original image will
now be shown by a 2x2 pixel square in the reduced image.

You can use a a"lossless compression" algorithm, but your camera has
already done that. The original image it took was a bitmap. The built
in software converted that to the *.jpg image that you copied to your
computer.

Bottom line: unless you have good reasons to do so, do not make image
files smaller. And if you must do so, always work ona copy, never on
the original image. FWIW, I have a "working copies" folder to ensure
that I don't mess with originals by mistake. Takes an extra step to copy
the image, but worth it.

HTH,
Wolf K.

Reducing picture size with same quality.
 

Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are
reduced to about 500KB with software such as Photoshop. When I take
small pictures with the camera the quality/definition is very good. I
don't want to take two shots of everything just to be able to get
small pictures for emailing. Why cant large quality pictures be
reduced to smaller ones - with the same definition?

Convert the large JPG image to a lossless format, like PNG, then reduce
that image.
--
Crash

English is not my native tongue; I'm an American.

Reducing picture size with same quality.
 

On Fri, 23 Mar 2012 13:43:22 -0400, "Dave \"Crash\" Dummy"
wrote:

Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are
reduced to about 500KB with software such as Photoshop. When I take
small pictures with the camera the quality/definition is very good. I
don't want to take two shots of everything just to be able to get
small pictures for emailing. Why cant large quality pictures be
reduced to smaller ones - with the same definition?

Convert the large JPG image to a lossless format, like PNG, then reduce
that image.

No smiley? :-)

--

Char Jackson

Reducing picture size with same quality.
 

On 23/03/2012 1:43 PM, Dave "Crash" Dummy wrote:
Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are
reduced to about 500KB with software such as Photoshop. When I take
small pictures with the camera the quality/definition is very good. I
don't want to take two shots of everything just to be able to get
small pictures for emailing. Why cant large quality pictures be
reduced to smaller ones - with the same definition?

Convert the large JPG image to a lossless format, like PNG, then reduce
that image.

Won't work if by "reduce the image" you mean "change pixel dimensions."

HTH
Wolf K.

Reducing picture size with same quality.
 

Wolf K wrote:
On 23/03/2012 1:43 PM, Dave "Crash" Dummy wrote:
Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good
quality camera. These are excellent, but I lose definition when
these are reduced to about 500KB with software such as Photoshop.
When I take small pictures with the camera the quality/definition
is very good. I don't want to take two shots of everything just
to be able to get small pictures for emailing. Why cant large
quality pictures be reduced to smaller ones - with the same
definition?

Convert the large JPG image to a lossless format, like PNG, then
reduce that image.

Won't work if by "reduce the image" you mean "change pixel
dimensions."

Depends on what you mean by "won't work." Any reduction is going to lose
detail because there are fewer pixels, but I have found that I get
better quality when I scale down a lossless format than I do when I
scale down a lossy one.
--
Crash

What happens online, stays online.

Reducing picture size with same quality.
 

Dave "Crash" Dummy wrote:
Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are
reduced to about 500KB with software such as Photoshop. When I take
small pictures with the camera the quality/definition is very good. I
don't want to take two shots of everything just to be able to get
small pictures for emailing. Why cant large quality pictures be
reduced to smaller ones - with the same definition?

Convert the large JPG image to a lossless format, like PNG, then reduce
that image.

Doing that might make sense if the JPG was Q=95 and 4MB in size, and
dropping to Q=10 would provide enough extra compression to shrink
the file (and degrade the quality of the image).

The question would be, whether PNG has a compression option, and
once the JPG is decompressed, the PNG compression is better than
the JPG compression (at whatever Q setting was used).

http://en.wikipedia.org/wiki/Portabl...cs#Compression

"Comparison to JPEG

JPEG uses a lossy encoding method specifically designed for
photographic image data, which is typically dominated by soft,
low-contrast transitions, and an amount of noise or
similar irregular structures.

Using PNG instead of a high-quality JPEG for such images would
result in a large increase in filesize with negligible gain in
quality.

By contrast, when storing images that contain text, line art,
or graphics – images with sharp transitions and large areas of
solid color – the PNG format can compress image data more than
JPEG can, and without the noticeable visual artifacts which
JPEG produces around high-contrast areas."

So PNG is kinda like GIF, in that it likes "cartoon" type
pictures, more than camera-captured pictures of natural scenes.

For the most part, if it's a camera, sticking with JPEG and
twiddling the Q knob, is a pretty good approach (in terms of
being easy to understand, and easy for a recipient to deal with).

HTH,
Paul

Reducing picture size with same quality.
 

On 23/03/2012 3:14 PM, Dave "Crash" Dummy wrote:
Wolf K wrote:
On 23/03/2012 1:43 PM, Dave "Crash" Dummy wrote:
Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good
quality camera. These are excellent, but I lose definition when
these are reduced to about 500KB with software such as Photoshop.
When I take small pictures with the camera the quality/definition
is very good. I don't want to take two shots of everything just
to be able to get small pictures for emailing. Why cant large
quality pictures be reduced to smaller ones - with the same
definition?

Convert the large JPG image to a lossless format, like PNG, then
reduce that image.

Won't work if by "reduce the image" you mean "change pixel
dimensions."

Depends on what you mean by "won't work." Any reduction is going to lose
detail because there are fewer pixels, but I have found that I get
better quality when I scale down a lossless format than I do when I
scale down a lossy one.

That's interesting, since AFAIK when the JPG is displayed or converted,
it's first reconstituted as a bitmap. Thus the quality of the resulting
PNG image would depend on the quality of the source JPG. AFAIK, the
scaling algorithm works on the actual JPG/PNG/etc data. If, as you say,
PNG reduced is better quality than JPG reduced, then there must be a
subtle differences in the algorithms. Or else the data structures differ
in what they conserve. Dash it all, now I'll have to do some research to
find out what's going on!

Anyhow, a JPG isn't necessarily lossy, it depends on the compression
ratio. Cameras generally use the lossless ("high quality") compression
ratio. Anyhow, all our cameras do so.

Many simple image-viewers/processors use a lower quality ratio by
default. You can find out if your does this by doing Save As on the
original image with small name change, then comparing the file sizes.
The programs I use offer setting the default compression ratio, so apart
from the effects of the processing itself, there is no change/loss in
quality.

HTH
Wolf K.

Reducing picture size with same quality.
 

On Fri, 23 Mar 2012 15:16:27 -0400, Paul wrote:

Dave "Crash" Dummy wrote:
Peter Jason wrote:
I have Win7 SP1. I take pictures of about 4 MB with a good quality
camera. These are excellent, but I lose definition when these are
reduced to about 500KB with software such as Photoshop. When I take
small pictures with the camera the quality/definition is very good. I
don't want to take two shots of everything just to be able to get
small pictures for emailing. Why cant large quality pictures be
reduced to smaller ones - with the same definition?

Convert the large JPG image to a lossless format, like PNG, then reduce
that image.

Doing that might make sense if the JPG was Q=95 and 4MB in size, and
dropping to Q=10 would provide enough extra compression to shrink
the file (and degrade the quality of the image).

The question would be, whether PNG has a compression option, and
once the JPG is decompressed, the PNG compression is better than
the JPG compression (at whatever Q setting was used).

http://en.wikipedia.org/wiki/Portabl...cs#Compression

"Comparison to JPEG

JPEG uses a lossy encoding method specifically designed for
photographic image data, which is typically dominated by soft,
low-contrast transitions, and an amount of noise or
similar irregular structures.

Using PNG instead of a high-quality JPEG for such images would
result in a large increase in filesize with negligible gain in
quality.

By contrast, when storing images that contain text, line art,
or graphics – images with sharp transitions and large areas of
solid color – the PNG format can compress image data more than
JPEG can, and without the noticeable visual artifacts which
JPEG produces around high-contrast areas."

So PNG is kinda like GIF, in that it likes "cartoon" type
pictures, more than camera-captured pictures of natural scenes.

For the most part, if it's a camera, sticking with JPEG and
twiddling the Q knob, is a pretty good approach (in terms of
being easy to understand, and easy for a recipient to deal with).

HTH,
Paul

Clearly this will take some research. I am impressed by the quality
of many Internet images that are merely about 150KB in size and yet I
cannot get mine anywhere near this quality, even with an expensive
camera. Would taking in RAW help, and using this in some imaging
software? I wonder how the Internet sites get their great detailed
pictures. Peter