[Histonet] Need help from Imaging Experts

[Philip Oshel]

Sharon,

I suggest PICT.
Short answer: always save original files in a format that does not 
compress the image *at all*. JPEG compresses images, even if (as in 
some programs) you have an option to use "0%" compression. (JPG2000 
may not use a lossy compression, but I'm not sure about that. I don't 
trust it.)
The saved file can then always be re-named ( ! ) and resaved as a 
JPEG if needed for e.g. emailing. The reverse is not true. Once an 
image is compressed, the information -- which means: your data -- 
discarded during compression is lost forever.

I ran a test on my Mac with iMovie, and saved a frame as a JPEG and a PICT.

Both files read as 1.5MB, and took 1.5MB memory, but the actual file 
length of the JPEG was 120kB, while the PICT was 1.5MB. JPEG 
compression was 1:12, there was no compression of the PICT image 
(strictly, compression was 1:1).

I then opened and saved both images as TIFFS using Graphic 
Converter**, and could see more detail and better color gradations at 
400% zoom in the file originally saved as a PICT. This was also true 
if just opening the saved PICT and JPEG images.

Keep in mind, once the frames have been saved as separate images, 
they can be opened and then saved in any other format. Adobe 
Photoshop CS2 (and I think earlier versions) in Windows opens PICT 
files.

The question becomes: what is the purpose of the images? If they are 
for posting on a web site, emailing, or a Powerpoint presentation, 
then JPEG is good. If they are for publication in print, or as a 
poster, then JPEG is no good. JPEG is a lossy file-compression 
standard. I believe PICT does not compress or lose image information.
(We at Microscopy Today don't like JPEG images for this reason, and 
always ask for micrographs as TIFFs. TIFFs are much larger files than 
JPEGs, but that is because JPEGs are compressed and have lost 
information.)

Note: iMovie saves at 72dpi if just "Saved", or exported for DV. If 
the movie is new -- i.e., not yet saved -- don't "Save" it, but 
"Export" it as "Full Quality". This will leave the individual frames 
uncompressed for later individual saving. This format can always be 
resaved for DV or CD-ROM if needed, but you will have kept all the 
information in the images.

**Graphic Converter is a shareware program that started life as a 
graphics file conversion program and has become an imaging program 
almost as powerful as Photoshop, but *much* easier to use. And costs 
$30. Anyone who has a Mac and does images should have this.
http://www.lemkesoft.com

Phil

>Here is my problem:  I can only use Mac iMovie to edit my digital 
>video.  I can not do this on a PC. ONLY iMovie.  To save a single 
>frame from the video, my choices are either PICT or JPEG format.
>
>My Question is: To save an origianl image, which is the best format, 
>PICT or JPEG?
>
>I'm not interested in hearing about Tiffs, BMPs or any other format 
>as that is not one of my choices.

-- 
Philip Oshel
Technical Editor, Microscopy Today
Microscopy Facility Supervisor
Biology Department
024C Brooks Hall
Central Michigan University
Mt. Pleasant, MI 48859
voice: (989) 774-3576
fax: (989) 774-3462