JPEG question

[juliadream]

I have a couple of imaging tools on my Windows XP system (Paint, PictureIt,
PhotoPlus, Adobe Photoshop Album). Out of all these, it is Paint that
achieves the best JPEG compression. Paint's JPEGs are sometimes 10 times
smaller that PhotoPlus' even though I'm compressing the same image using
identical parameters (image size, number of colours, etc).

How is this possible? When I look at the resulting images, the 5MB JPEG
(PhotoPlus) and the 500K JPEG (Paint) are indistinguishable.

 

[Yves Alarie]

The smaller size is achieved by Paint because it uses a higher compression
level.
Just like you have a choice in your camera to save the file at different
compression levels.
I agree it is difficult to see the difference, unless you really look and
you cannot do this by opening one image and then opening the other. You need
to compare the images side by side on your screen or on prints and unless
you look at the images enlarged on your screen you are unlikely to see the
differences. Same with prints, you need large prints.
You can download this free image viewer to do this:
www.faststone.com
Select the two images and compare (a compare icon is on the top bar to
compare up to 4 images).
When the images open, enlarge them with the mouse wheel and at one point you
will begin to see the differences. Sharp edges will become less sharp and
colors will begin to fade.
With this same viewer, open an original file and then Save as and click on
the Advanced button. This will give you a slider to reduce the file size
(increase the compression level). Save at different compression levels and
then compare.

 

[juliadream]

The smaller size is achieved by Paint because it uses a higher compression
level.
Just like you have a choice in your camera to save the file at different
compression levels.
I agree it is difficult to see the difference, unless you really look and
you cannot do this by opening one image and then opening the other. You
need
to compare the images side by side on your screen or on prints and unless
you look at the images enlarged on your screen you are unlikely to see the
differences. Same with prints, you need large prints.
You can download this free image viewer to do this:
www.faststone.com
Select the two images and compare (a compare icon is on the top bar to
compare up to 4 images).
When the images open, enlarge them with the mouse wheel and at one point
you
will begin to see the differences. Sharp edges will become less sharp and
colors will begin to fade.
With this same viewer, open an original file and then Save as and click on
the Advanced button. This will give you a slider to reduce the file size
(increase the compression level). Save at different compression levels and
then compare.

Thanks for your response. PhotoPlus allows you to load multiple images and
compare them. I loaded both images side-by-side and zoomed into the finest
details (eyes, hair, etc). No matter how much I zoomed in, there's seemed
to be no difference (both images got equally distorted). I'm sure Paint's
algorithm is more lossy but I can't detect these losses even at zoom 5:1.

 

[Yves Alarie]

I don't have Photo Plus so I did not know if you could do this test with it.
Indeed it is not that easy to see differences, but it also depends on the
quality of your video display.
I can see the difference, but you have to know where to look and if are not
aware about where to look then you will miss it. Nothing wrong with this.
You are looking at the "whole" picture, I am looking where I know high
compression jpg will make a difference, but it will make a difference in
specific areas of the picture, not the whole picture.
One thing you can do is set up an experiment to really see the differences.
You take a white piece of paper and you draw straight black, red, blue any
color lines about one quarter of an inch thick. Then set your camera on a
tripod or just on a solid surface and take a picture at each of your camera
jpg compression settings.
JPG compression is poor for this kind of scene and you will see
deterioration fairly quickly. You can then take your highest compression
picture and save it in Paint and compare. You should be able to see the
difference immediately. You will not be distracted by the "whole" picture,
because there is no picture there, just lines and colors to look at. Unless
you have a very poor video display, the differences should jump at you.
Your original question was (and still is) very good. Indeed why is this
happening?
It is worth understanding what is going on and find where the limitations
are for the type of finished product one is looking for.

 

[Dave Hart]

I don't understand the file sizes you're getting.
I took a 9Mb bitmap image and saved it as JPEG
in each of Paint, Paint Shop Pro and PhotoPlus.
These are the resulting sizes I got:
Paint 208Kb
Paint Shop Pro 422Kb
PhotoPlus 283Kb

Dave Hart

 

[juliadream]

I don't understand the file sizes you're getting.
I took a 9Mb bitmap image and saved it as JPEG
in each of Paint, Paint Shop Pro and PhotoPlus.
These are the resulting sizes I got:
Paint 208Kb
Paint Shop Pro 422Kb
PhotoPlus 283Kb

I have not been able to get numbers that are so closely matched. Paint's
compression is anywhere from 3x to 10x times better than PhotoPlus
(depending on the image). All images are pictures of people and faces,
taken with a digital camera. I'm currently going through all my JPEGs and
re-saving them with Paint.

 

[Yves Alarie]

Can you tell me if these JPEG files are coming from a digital camera or a
scanner?

 

[Jim]

I have a couple of imaging tools on my Windows XP system (Paint, PictureIt,
PhotoPlus, Adobe Photoshop Album). Out of all these, it is Paint that
achieves the best JPEG compression. Paint's JPEGs are sometimes 10 times
smaller that PhotoPlus' even though I'm compressing the same image using
identical parameters (image size, number of colours, etc).

How is this possible? When I look at the resulting images, the 5MB JPEG
(PhotoPlus) and the 500K JPEG (Paint) are indistinguishable.

The various programs use varying amounts of compression. Photoshop (amoung
many others) lets the use select the amount of compression.
As for your second question, you might not be able to detect any difference
until after you had saved each image quite a few times. You also might
never be able to detect any difference when viewing on a monitor.
Jim

 

[Rehan]

I'm currently going through all my JPEGs and re-saving them with Paint.

Paint may also be discarding the EXIF data associated with the JPEGs from
your camera. This is important info so you should keep the originals.

Furthermore the default quality for saving jpegs in paint is around 75%
while in other apps it is near 100%. Hence the size difference.

Presumably you want small filesizes so that you can send these pictures to
somebody via email or something? If so you can get the Image Resizer
powertoy and save all of your images in one go with 75% quality (by
specifying the same size as input) or even resize them as well to reduce
their filesize even more.
http://www.microsoft.com/windowsxp/downloads/powertoys/xppowertoys.mspx

 

[igno]

The smaller size is achieved by Paint because it uses a higher compression
level.
Just like you have a choice in your camera to save the file at different
compression levels.
I agree it is difficult to see the difference, unless you really look and
you cannot do this by opening one image and then opening the other. You need
to compare the images side by side on your screen or on prints and unless
you look at the images enlarged on your screen you are unlikely to see the
differences. Same with prints, you need large prints.
You can download this free image viewer to do this:
www.faststone.com
Select the two images and compare (a compare icon is on the top bar to
compare up to 4 images).
When the images open, enlarge them with the mouse wheel and at one point you
will begin to see the differences. Sharp edges will become less sharp and
colors will begin to fade.
With this same viewer, open an original file and then Save as and click on
the Advanced button. This will give you a slider to reduce the file size
(increase the compression level). Save at different compression levels and
then compare.

I received an attachment jpg file 41.0KB and saved it as jpg file in
GIMP, Irfanview,Adobe Photo Album and in Paint.
I got the following sizes 33.2KB, 66.6KB,36.8KB and 25.5 KB
respectively. I could not find any difference in the four pictures ---
but my eyes are gone and I am semi blind. I also tried at different
screen resolutions 800X600 and 1024X768 --- the same thing.