[Gimp-user] Bit-depth Processing

[gimp_user]

On Tuesday 02 October 2007 11:58:47 Greg wrote:
> --- Patrick Shanahan <ptilopteri at gmail.com> wrote:
> > Then you need to abandon the jpeg format as it is lossey (google for
> > it) and you need to shoot RAW.
>
> I know, but if you can retain your original bit-depth, the lossyness
> isn't as noticeable, especially if you set the compression to the
> lowest possible.  At least, that's my understanding.
>
>
This is true for the first iteration. Unfortunately intermediate saves work 
rather like     sound recordings.. there is some additional  loss at each 
stage and the effect of the lossyness of the format is therefore multiplied. 
The effect of lossyness can reduce the effectiveness of some editing and 
image manipulation algorythms.

Even at minimum compression there is lossyness. On the other hand lossyness of 
a reasonably high resolution digital image does not matter of you are using 
an overhead projector at 1024x768. You can increase the degree of compression 
quite substantiallly before the difference is really noticeable. In fact OHP 
can make images which would be panned, or even appear unsharp when printed as 
a large print, can appear really attractive when projected at 1024x768. 

But try to create a large high resolution image (or apply substantial 
enlargment to a portion of an image), then the results of lossyness are 
quickly all too apparent.

I practise trying to define my target final output from a sourced image. 
However I cannot always accurately predict how an image will finally be used 
so I tend to opt for working with a raw image unless I know the the final 
media will be in a comparatively low resolution and with a constrained gamut. 
After all the problems of scaling an image to a lower reolution/gamut are 
minimal by comparison with the limitation inherent in trying to scale up.

My two pennorth