[photo-3d] Re: Question for newsletter editors - pdf picture quality

["Ray Moxom" <raymoxom@xxxxxxxxxx>]

The crux of DrTs question on producing 3D pdf bulletins is (note the 3D!):
> What is the best strategy to follow for best results,
> regarding the format and compression that the images
> are saved and imported into the newsletter?

Lots of off topic questions George.

At the risk of us both being vilified let us try to solve some of these
dreaded 'pdf' issues. I must first say that I do not always do all the
recommended things myself due to time and available images etc.

The main factors that impact on resolution and file size at the 'printing'
to PDF stage seem to be the "Downsample Images" option and the "JPEG
compression" option. Both of these options are under "Compression Options".
It also seems that the "Downsample Images" option has a greater impact on
image quality than JPEG compression.

I generally use the 'JPEG High' (highest compression) setting and the
"Downsample Images" option. This results in relatively low quality images
but an acceptable file size for sending a 20 page colour photo bulletin by
email.

If the images are all edited to 72 ppi and to the actual size that they will
appear, then there is no need to use the  "Downsample Images" option and the
quality will be higher for the same file size.

If picture files need to be saved at an intermediate stage before they are
in their final, ready to insert, stage - then save them as bitmap files and
only save the final JPEG file once. As Peter Davis "each time you
de-compress and re-compress JPEG images you lose some quality".

Below are two examples:

Example # 1
Seven photos plus text, all photos actual size  of about 140 mm wide and 72
ppi
A. JPEG High with Downsample Images - file size = 294kb
B. JPEG High and no Downsample Images - file size = 294kb
C. JPEG Med-High and no Downsample Images - file size = 389kb
A and B are the same file size, but B seems to be of higher quality.

Example # 2
One photo plus text, photo actual size of about 140 mm wide and 150 ppi
D. JPEG High with Downsample Images - file size = 64kb
E. JPEG High and no Downsample Images - file size = 136kb
F. JPEG Med-High and no Downsample Images - file size = 180kb
D is of poor quality - E & F seem to be of similar quality.

I will temporally upload these six files to the files section of this list.
File names will start with the above letters. Folder name is 'PDF Test Files
'.

File size is very important and everything is a compromise. Creating PDF
files at the highest possible resolution would, in my case, result in
bulletin files of several Mb that would be near impossible to email or
upload to many sites.  Even the eGroups files area has a file size limit
that seems to be at about the 1Mb mark.  I think that the upper practical
limit is closer to 500Mb to ensure reasonable download times.

Ray Moxom