What benefit .png over .jpg?

[joe at actionline.com]

Just for a comparison test ...

Yesterday, I used a professional photographer's raw source, converted to a
'tif' file that was 156-megabyte for a single portrait image 3744 x 5616
pixels and shown to be 15.600" x 23.399" at 240 pixels/inch to do a print
quality comparison.

So exhibit #1 was a 'tif' file with a size of 155,861,380.

>From that source, I used gimp to convert it to a .jpg at 100% quality, and
the result was a 11 megabyte file.

So exhibit #2 was a 'jpg' with a file size of of 10,990,434.

For exhibit #3, with gimp, I also saved the same image at the gimp default
quality of 85% which created a file size of 2 megabyte - actually:
1,815,303.

For exhibit #4, I used gimp to scale the image down to 1280 x 1920 saved
as jpg at 85% quality which created a file size of 1/4th of a megabyte -
actually 225,492 bytes.

For exhibit #5, I further scaled the image down to 8" x 12" at 100
pixels/inch and saved it as a jpg with a file size of 1/10th of a megabyte
- actually 121,542.

I sent all five files to Costco to print as 8" x 12" with random letters
assigned to each file/image.

I seriously doubt that anyone could tell any difference between any of
these five images with a naked eye.  I have nearly perfect vision and I
studied them with a magnifying glass and cannot tell any difference in the
first four and only I can only tell an almost imperceptible difference
between exhibit #1 and exhibit #5 by using a jeweler's loop.



--------------------
> ... the relatively cheap digicam I bought in 2002 saved date/time,
> effective f-stop, shutter speed, effective ISO, and various other
> things in an EXIF block within the JPEGs it produced. The slightly
> better digicam I have now does the same thing, and it can't produce
> anything but JPEGs.
[snipped]
> ... It just depends on how much disk space you'd like to
> devote to storing stuff.  Since I'm not a professional photographer, I
> find that 3500x2600 JPEGs at 90+ quality (about 2.2M per JPEG) seem to
> work great for what I need.