Paint Shop Pro support - What does easy compression tell me about a jpeg?

Author

What does easy compression tell me about a jpeg?

Zak

2006-05-15, 4:13 am

Sometimes I compress a jpeg which I have downloaded from the Net.

I always use the same old version 3.1 of ACDSEE for compression mainly
because it is simple and convenient although I do have Photoshop and
Paint Shop Pro. However I tend not to use them for something which
seems so straightforward.

As an example, I notice that (with the SAME settings for compression in
Acdsee) some 500 KB jepgs will compress to 300 KB but other 500 KB jpegs
will compress right down to a surprisingly small 100 KB.

What does the final size in KB compared to the original size tell me
about the properties of original jpeg?

Or to put it another way, how is the degree of compression (given the
same settings on Acdsee) linked to the original jpeg's properties such
as pixel size, print size, etc?

Andrew Morton

2006-05-15, 6:59 am

Zak wrote:
> As an example, I notice that (with the SAME settings for compression
> in Acdsee) some 500 KB jepgs will compress to 300 KB but other 500 KB
> jpegs will compress right down to a surprisingly small 100 KB.
>
> What does the final size in KB compared to the original size tell me
> about the properties of original jpeg?

Nothing. The file size is related to how much detail there is in the image.
More detail<=>larger file.

> Or to put it another way, how is the degree of compression (given the
> same settings on Acdsee) linked to the original jpeg's properties such
> as pixel size, print size, etc?

It isn't.

Andrew

Mike Russell

2006-05-15, 6:59 am

"Zak" <duff@nomail.invalid> wrote in message
news:Xns97C44F19D7AEF64A18E@127.0.0.1...
> Sometimes I compress a jpeg which I have downloaded from the Net.
>
> I always use the same old version 3.1 of ACDSEE for compression mainly
> because it is simple and convenient although I do have Photoshop and
> Paint Shop Pro. However I tend not to use them for something which
> seems so straightforward.
>
> As an example, I notice that (with the SAME settings for compression in
> Acdsee) some 500 KB jepgs will compress to 300 KB but other 500 KB jpegs
> will compress right down to a surprisingly small 100 KB.
>
> What does the final size in KB compared to the original size tell me
> about the properties of original jpeg?
>
> Or to put it another way, how is the degree of compression (given the
> same settings on Acdsee) linked to the original jpeg's properties such
> as pixel size, print size, etc?

Jpeg uses an adaptive algorithm for compression. Lower quality numbers
result in smaller files, but the actual size, as you imply, depends on the
amount of detail contained in the image. File size, and therefore jpeg file
size does not depend on the pixel size or print size of the image, since
these are ancillary data that are unrelated to image content.

For example, a 512x512 image containing only white will save to 14KB at jpeg
quality 10 in Photoshop, while the same size image containing gaussian noise
compresses to 695KB. Blurring the noise image by .5 pixel results in a 424
KB jpeg image.

Normal photographs will vary between these two extremes, with the biggest
variable probably being the amount of noise in the image. Certain material,
such as scanned cartoons, will save smaller and at a higher quality as gif
images, or RLE encoded tiff images, than as compressed jpegs. Each RGB
channel is compressed separately, and in theory a somewhat smaller image
could be achieved by jpeg compressing an Lab image, with a higher quality
for the Lightness channel.
--
Mike Russell
www.curvemeister.com/forum/

Mike Russell

2006-05-15, 6:59 am

"Mike Russell" <RE-MOVEmike@Curvemeister.comRE-MOVE> wrote in message
news:aPX9g.16985$Lm5.13553@newssvr12.news.prodigy.com...
> Each RGB channel is compressed separately, and in theory a somewhat
> smaller image could be achieved by jpeg compressing an Lab image, with a
> higher quality for the Lightness channel.

Oops - scratch that. Jpeg images do not compress the RGB channels
separately, but treat color data separately from luminance.
--
Mike Russell
www.curvemeister.com/forum/

tacit

2006-05-15, 11:08 pm

In article <Xns97C44F19D7AEF64A18E@127.0.0.1>,
Zak <duff@nomail.invalid> wrote:

> As an example, I notice that (with the SAME settings for compression in
> Acdsee) some 500 KB jepgs will compress to 300 KB but other 500 KB jpegs
> will compress right down to a surprisingly small 100 KB.

A lot depends on how much the JPEG was compressed to begin with.

If it was originally compressed with a high quality setting, and you
save it from ACDSee with a medium quality setting, it may shrink a bit.
If it was originally saved with an extremely high quality setting, and
oyu save it with a medium quality setting, it may shrink quite a lot.

--
Art, photography, shareware, polyamory, literature, kink:
all at http://www.xeromag.com/franklin.html
Nanohazard, Geek shirts, and more: http://www.villaintees.com

Uni

2006-05-16, 5:05 am

tacit wrote:

> In article <Xns97C44F19D7AEF64A18E@127.0.0.1>,
> Zak <duff@nomail.invalid> wrote:
>
>
>
>
> A lot depends on how much the JPEG was compressed to begin with.

Sort of, no, more like, how well a text file will zip/compress.

:-)

Uni

>
> If it was originally compressed with a high quality setting, and you
> save it from ACDSee with a medium quality setting, it may shrink a bit.
> If it was originally saved with an extremely high quality setting, and
> oyu save it with a medium quality setting, it may shrink quite a lot.
>

Zak

2006-05-17, 7:12 pm

On 15 May 2006, Mike Russell<RE-MOVEmike@Curvemeister.comRE-MOVE>
wrote:

>
> Jpeg uses an adaptive algorithm for compression. Lower quality
> numbers result in smaller files, but the actual size, as you imply,
> depends on the amount of detail contained in the image. File size,
> and therefore jpeg file size does not depend on the pixel size or
> print size of the image, since these are ancillary data that are
> unrelated to image content.
>
> For example, a 512x512 image containing only white will save to
> 14KB at jpeg quality 10 in Photoshop, while the same size image
> containing gaussian noise compresses to 695KB. Blurring the noise
> image by .5 pixel results in a 424 KB jpeg image.

So blurring will result in a larger file size? That may explain it. I
see some very sharp pictures with what seems to be decent detail be
quite compressible.

Whereas poorer quality images (perhaps poor scans, images that have been
tinkered with, poor photo equipment if photo is very old) do not
compress corrtespeondingly better.

I thought the poorer the quality of the jpeg the more it would compress
but I guess that often it is the other way around.

Is my understanding broadly correct?

>
> Normal photographs will vary between these two extremes, with the
> biggest variable probably being the amount of noise in the image.
> Certain material, such as scanned cartoons, will save smaller and
> at a higher quality as gif images, or RLE encoded tiff images, than
> as compressed jpegs. Each RGB channel is compressed separately,
> and in theory a somewhat smaller image could be achieved by jpeg
> compressing an Lab image, with a higher quality for the Lightness
> channel.

Mike Russell

2006-05-17, 7:12 pm

From: "Zak" <duff@nomail.invalid>
....
> So blurring will result in a larger file size? That may explain it. I
> see some very sharp pictures with what seems to be decent detail be
> quite compressible.

No - the other way around. Blurring results in a file that compresses more
efficiently.

> Whereas poorer quality images (perhaps poor scans, images that have been
> tinkered with, poor photo equipment if photo is very old) do not
> compress corrtespeondingly better.

Adding noise, sharpening, increasing contrast, all tend to make the
resulting jpeg larger.

> I thought the poorer the quality of the jpeg the more it would compress
> but I guess that often it is the other way around.
>
> Is my understanding broadly correct?

In general, good clean scans will very little noise will compress better
than noisy scans. Because most edits result in increased contrast and
color, manipulated images, with certain exceptions, will generally be larger
than unmanipulated ones.
---
Mike Russell
www.mike.russell-home.net

2006-05-17, 7:12 pm

"Mike Russell" <RE-MOVEmike@Curvemeister.comRE-MOVE> wrote in message
news:5gEag.88723$dW3.9545@newssvr21.news.prodigy.com...
> From: "Zak" <duff@nomail.invalid>
> ...
>
> No - the other way around. Blurring results in a file that compresses
> more efficiently.

Question Mike: Gaussian blurr is, by definition, not an even blur (although
it is 'regular'), so adjacencies calculate to differences that do not
compress well. Is that correct?

Mike Russell

2006-05-17, 7:12 pm

From: "2" <nhoj@droffats.ten>
....
> Question Mike: Gaussian blurr is, by definition, not an even blur
> (although it is 'regular'), so adjacencies calculate to differences that
> do not compress well. Is that correct?

Gaussian refers to the "shape" that is used to distribute pixel values when
calculating the blur. It tapers off gradually, and would produce a slightly
smaller jpeg file than, for example, a box blur which has sharp edges.
---
Mike Russell
www.curvemeister.com/forum/

David Gilbert

2006-05-17, 7:12 pm

On Wed, 17 May 2006 15:32:14 GMT, "Mike Russell"
<RE-MOVEmike@Curvemeister.comRE-MOVE> wrote:

>From: "2" <nhoj@droffats.ten>
>...
>
>Gaussian refers to the "shape" that is used to distribute pixel values when
>calculating the blur. It tapers off gradually, and would produce a slightly
>smaller jpeg file than, for example, a box blur which has sharp edges.
>---
>Mike Russell
>www.curvemeister.com/forum/

Original image 2,046,076 bytes
Compressed JPG (15, 1.1.1.) 127,066 bytes
Compressed JPG (15, 1.1.1.) Blur More 106,958 bytes
Compressed JPG (15, 1.1.1.) Gaussian 1 112,566 bytes
Compressed JPG (15, 1.1.1.) Gaussian 2 100,179 bytes
Compressed JPG (15, 1.1.1.) Gaussian 5 91,055 bytes

--
Regards
David: NorthWest, England