Re: Vuescan - new features

In article <3np5p11hrm64mt3a9bk1a3c141d9vhngnd@xxxxxxx>,
Don <phoney.email@xxxxxxxxx> wrote:
>On Sun, 4 Dec 2005 00:44:58 +0100, philip@xxxxxxxxxxxxxxxxx (Philip
>Homburg) wrote:
>>Typically in a curves window, you can just select a point on the
>>curve, and move it up or down. The uncorrected image does not appear as
>>input.
>
>Yes, you can set points directly (i.e. blind) in the curve but that's
>a very blunt instrument. Doing that means making assumptions about the
>image. For example, using the "standard" S curve (64,128,192) assumes
>where the shadows, midtones and highlights are.
>
>However, even in that case, basing this "blind" setting on a gamma 2.2
>image while the curve is applied to a gamma 1.0 image doesn't get
>around that root problem.

It is the curve that matters, not where the control points are. Selecting
a curve is an interactive/iterative process. Getting some idea where the
'bad' parts of the image fall on the curve is useful, not not required.

For proper control, it is probably best of the curve window is based on LAB,
the input is based on XYZ and the display is based on the monitor profile
(typically around gamma 2.2).

>>It is possible that
>>Vuescan fails to apply gamma in this case, but that is just a one line fix.
>
>It wouldn't be the first time that Vuescan fails to do the simplest of
>things which is precisely why it can be justifiably described as buggy
>and unreliable.

That depends. If new features don't work the first time, send a detailed
bug report to the author and it will probably be fixed.

I don't have a Vuescan license because I can usually live with the limitation
of the vendor supplied software.

But the trail versions I tried were never buggy in my experience. Just
not worth the money.

>>If you select bin 128 in the window, then yes, you may end up changing bin
>>56 in the 2.2 gamma corrected image. But the 2.2 gamma correct image is only
>>there to display what you are doing. The real image is in gamma 1.0.
>
>Which is precisely the root of the problem, apparently.

That is not the root problem. It is supposed to work like that.

>>You 'cannot' display a gamma 1.0 image directly.
>
>I notice quotes around 'cannot' which means you know what I'm going to
>say (so just ignore the next bit) but for the benefit of kibitzers:
>
>Actually, one can. That's what linear editing is all about. One simply
>recalibrates the monitor to gamma 1.0 as well and then the image does
>not appear "dark and contrasty".

The 'cannot' is there for two reasons:
1) of course you display a gamma 1.0 image directly on a gamma 2.2 monitor:
it just won't look very good.
2) as far as I know all my graphics cards have 8-bit/ch D/A converters and
8-bit/ch is not enough for gamma 1.0. Of course there is the additional
problem that in general monitors don't support gamma 1.0 anyhow.

(Trying to use 8-bit/ch LUTs to convert from gamma 1.0 to 2.2 is bound to make
things even worse).

>But even in that case looking at one image while editing another (in
>the current context) is just asking for trouble. But such convoluted
>contraptions are one of the major trademarks of Vuescan and why it is
>so buggy and unreliable.

Looking at one image while editing another is exactly what my XYZ library
does. There is no magic there. (Of course, if you select in Photoshop
any color space other the monitor color space, you end up with the same
thing. Typically not with luminance, but with saturation).


--
That was it. Done. The faulty Monk was turned out into the desert where it
could believe what it liked, including the idea that it had been hard done
by. It was allowed to keep its horse, since horses were so cheap to make.
-- Douglas Adams in Dirk Gently's Holistic Detective Agency
.

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