Reducing picture size with same quality.

[Peter Jason]

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

 

[Monty]

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.

 

[Paul]

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

 

[Rob]

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/...indows-7/a30f4dae-0e89-448f-9659-ad9acd370b9b

 

[Vic RR Garcia]

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).....

 

[J. P. Gilliver (John)]

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.

 

[Ken Springer]

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

 

[Wolf K]

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.

 

[Dave \Crash\ Dummy]

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.

 

[Char Jackson]

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

No smiley?

 

[Wolf K]

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.

 

[Dave \Crash\ Dummy]

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.

 

[Paul]

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/Portable_Network_Graphics#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

 

[Wolf K]

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.

 

[Peter Jason]

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/Portable_Network_Graphics#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

 

[JD]

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

Maybe you could tell us how you are re-sizing the pictures? Details!

 

[Ken Springer]

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

Way, way back in the dark ages of computing, i.e. the 1980's and '90's,
I was experimenting with desktop publishing.

The rule was, *never* convert the photo to a lossy format like JPG,
until you are finished manipulating the photo. That was before digital
cameras, and you scanned your photos. Make a copy of the file you
scanned, and work on the copy. Make a lot of saves, changing the name
slightly each time, just in case things didn't work out the way you wanted.

I would still use a RAW or Tiff image, or some other lossless file
format, today if my consumer digital camera gave me the option of
something other than JPG.


--
Ken

Mac OS X 10.6.8
Firefox 10.0.2
Thunderbird 10.0.2
LibreOffice 3.5.0 rc3

 

[Paul]

Way, way back in the dark ages of computing, i.e. the 1980's and '90's,
I was experimenting with desktop publishing.

The rule was, *never* convert the photo to a lossy format like JPG,
until you are finished manipulating the photo.

Sage advice.

You use whatever techniques you can which lose as little information
as possible, before creating the final output. If you decompress,
recompress, decompress, recompress with a chain of JPEG transactions,
it'll "let all the air out of your tires". JPEG should be saved for
the final conversion before emailing. A lossless format should be
used up to that point. (One would hope RAW is such a format.)

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

"Raw files are so named because they are not yet processed and therefore
are not ready to be printed or edited with a bitmap graphics editor.
Normally, the image is processed by a raw converter in a wide-gamut
internal colorspace where precise adjustments can be made before
conversion to a "positive" file format such as TIFF...

These images are often described as "RAW image files", although
there is not actually one single raw file format."

So RAW comes out of the camera, but you use the camera software to make
a standard image format. And at that point, should be selecting a lossless
or no-compression format. JPEG would not be appropriate (even with Q=100)
at that point. Once all your intermediate edits are finished, the
result can be saved twice, once in a lossless format, and a second
time in JPEG for the email. If you use a quality setting of 10% (Q=10),
that gives 50:1 compression or thereabouts for the JPEG. Although I probably
wouldn't send a picture like that, I might be tempted to use that
low a Q, if the recipient is a dialup networking user. If the person
has a broadband connection, I'd send a larger image. Some email
services will handle 10 to 20 MB files, without resorting to chopping
the thing in pieces and using more than one email message.

One secret to good pictures, is lots of light, and low noise
sensors. The $100 webcam, has a lot of noise modulation on
the image it captures. And when you shove that into a JPEG
compressor, the file size bloats up. If you use a $10K camera,
there's a good chance the noise level is lower, and the image
will be more compressible.

When I want to reduce noise in a picture (with my $100 webcam),
I take still photos of non-action scenes, and I shoot the same
picture twice (same lighting). Then, I use Photoshop averaging
(A+B divided by 2). When you average two noisy pictures together,
the noise level is reduced in the final picture. If you had a
good camera, that probably wouldn't be necessary - but nothing
I own falls into the "good" category

Paul

 

[Bob L]

Have you tried Irfanview and use the re-sample instead of re-size ? It
givess better results than resize.

 

[Justine Time]

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 use Paintshop Pro X2 and have similar probs if I want to resize an image.
I now use a small free bit of software to do the resizing. Simple and
works great (Easy thumbnails)

Here is a an original pic from my camera reduced down in size 5 times.
From 2848x2136 to 88x66
(Large file so may be slow to show)

http://www.steveonline.info/test1.html