Using compression to reduce file size

[Ken Johnson]

On my worksheet I'm using around 30 jpeg images that need cropping and
reducing down to around to 5% of original size.
I'm compressing the images to minimise file size.
Will the order of compressing and reducing matter?
Should I crop, compress then reduce or crop reduce then compress, or
will it not make any difference to the printed worksheet.
I can't see any difference, but that doesn't mean the order of
processes doesn't matter.

Ken Johnson

 

[SteveW]

jpeg files are compressed already.
re-generating a lower level jpeg file will lose quality.
The best bet is to crop, reduce in size - then if still needed re-generate
test the resulting image to ensure you can still see what you want.

Steve

 

[Ken Johnson]

Thanks Steve.
Recompressing of just one image changes the file size from 380 KB to 19
KB with little drop in quality so I guess I leave the compression till
last and do all the reduced images in one go.

Ken Johnson

 

[SteveW]

You have a jpeg file of 380kb and compress it (with zip) and get 19kb

Very suprised ?

Steve

 

[Ken Johnson]

You have a jpeg file of 380kb and compress it (with zip) and get 19kb

Very suprised ?

Hi Steve,

I compress using the compression tool on the Picture toolbar that is
part of Excel 2003.

Ken Johnson

 

[Earl Kiosterud]

Joe,

Some thoughts: If you've cropped the images with the picture toolbar, it
retains the entire image unless you also use the "Compress" tool with the
"delete cropped parts" in the Format - Picture dialog.

As for the workbook size, Excel seems to store the compressed image in the
workbook file, unlike with sheet backgrounds, where it stores the
uncompressed image. The compress tool in the Format - Picture dialog
reduces the file size considerably, and blurs the picture slightly. Oddly,
it doesn't seem to add compression artifacts as happens when the jpeg
compression is increased. Perhaps that's because it's been first blurred.
If you're making the images small, that may be suitable for your
application. If not, then you might get better results with an image
editor, where you can do things like save it with increasing compression,
finding the best compromise.

 

[SteveW]

I haven't got that yet

Still suprised.

Either your originals arn't jpeg's but are bmp's or Excel is compressing
them using a very low jpeg calculation level

Anyway...

Steve

 

[Ken Johnson]

Joe,

Some thoughts: If you've cropped the images with the picture toolbar, it
retains the entire image unless you also use the "Compress" tool with the
"delete cropped parts" in the Format - Picture dialog.

As for the workbook size, Excel seems to store the compressed image in the
workbook file, unlike with sheet backgrounds, where it stores the
uncompressed image. The compress tool in the Format - Picture dialog
reduces the file size considerably, and blurs the picture slightly. Oddly,
it doesn't seem to add compression artifacts as happens when the jpeg
compression is increased. Perhaps that's because it's been first blurred.
If you're making the images small, that may be suitable for your
application. If not, then you might get better results with an image
editor, where you can do things like save it with increasing compression,
finding the best compromise.

Thanks Earl,

The resulting quality does suit my application, and the file size has
been reduced to around 700 KB from 7 MB.
It will ultimately be printed on a b/w laser, which seems to produce
slightly clearer results (less blurred) than my home inkjet.
I'll see what can be achieved using photoshop. If it gives a better
result then I may as well use it.

Ken Johnson