On Mon, Apr 03, 2000 at 10:30:47PM +0100, Nick Lamb <[EMAIL PROTECTED]> wrote:
> This isn't true, IJG documentation and home made tests show that, for

Yes, this is true. You (and the ijg group) assume that the image does not
change between the load/save cycle.

> This isn't guaranteed, but will usually work if you keep everything the
> same (codec, compiler, libraries, CPU, direction of the wind...)

(... image content)

As such, why save an image if you didn't change it?

> In any case it never does any harm. In fact, this improvement can be
> enough for the difference between "obviously re-edited JPEG" and a
> seamless fix to an image when you've lost the original.

Given that the problem is unsolvable in theory and almost impossible even
to approximate in practise, I believt hat such a automatic detection
scheme will fool people into thinking that saving at the same quality
wouldn't destroy their image.

> the IJG codec was used at all. IMHO that's for the best. I should not
> need to care which encoder was used to use the image.

The problem here is that different encoders have different notions of
"quality settings", and in most cases you can only approximate the
quality setting of another encoder (quality settings are just a quick
way to describe a 8x8 matrix, and setting up that matrix is very much

      -----==-                                             |
      ----==-- _                                           |
      ---==---(_)__  __ ____  __       Marc Lehmann      +--
      --==---/ / _ \/ // /\ \/ /       [EMAIL PROTECTED] |e|
      -=====/_/_//_/\_,_/ /_/\_\       XX11-RIPE         --+
    The choice of a GNU generation                       |

Reply via email to