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

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.

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

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

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).....

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...

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

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.

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.

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