Re: [APML] Fw: images

["Carlos Milovic F." <cmilovic@yahoo.es>]

>> I don't understand what you are saying...
>I'm saying the human eye can see a much greater brightness range >than a
>monitor or print can display. I think we agree here.

Yes. And I was saying that the human eye can see the steps in a gray gradient from black to white (from the monitor, for example) only if the precition is less than nearly 7bits

> >Perhaps, but compare my 10 bit image example to any astrophoto.
> Ok. Here we are talking about diferent matters. Astrophotos make use
> of other zones in the dinamical range, and usually the information we
> want (don't think on the stars, they cover the whole Drange) is
> located in very few levels.

>> I recognice that indeed if we count how many levels we use from the
>> original scan it could be 2^6 per channel (in a 16bits file, scanned
>> at 10bits). Anyway, it doens't mean that film has a bit deph of 6bits.
>For some reason I can't make myself clear. I'll try again. I never said
>(or at least meant) film in general can't represent more than 6 bits. I
>said astrophotos on film can't.

Ok. And my point is that this is only a limitation of the scanning process and not due the film's capabilities of "storing the information". That was the point I was trying to reach with the "experiment" below.

 

BTW, all of these started becouse I said that we are not limited to 8bits using film. If we compare the "raw" 16bits from a CCD image and what we could digitalice from a film... is it just 8bits?

BTW2, Could be the difference in the final bit deph of a astropic between CCD and film mainly due the mayor "latitude" of CCDs (no staking)?

>> I prefer to talk about bit deph just as a matter of precition...
>> Imagine that we have nice curves controls in the scanning process, and >> that we can scan the original and obtain the directly "final" result.
>> How many grays do we have? Think that the colors are represented in >> the 0 - 1 range, with the 16 bits as precition. I think that we'll
>> have more than 64 grays. Perhaps not 2^16, becouse the original data >> isn't stored strictically as a continuom in the film, but indeed more
>> than 64.

>I think you're overestimating how many gray levels are necessary for a
>nice looking image. I'd be really happy if ever one of my TP images had
>64 noise-free gray levels.

I have to agree here... but I think that today we can obtain images with more than those levels without noise (using the appropiate software and scanning process).

>> Use large radii to blur a astronomical image, just as if you were
>> creating an AV mask with that procedure.
>Now I see it but only with the guassian blur, not with a continuous
>gradient.

 

The later is by far much more difficult to cath. I'll search for an example in my files... Anyway, try gradients between very few levels.

 

> Those steps are only one level.

 

Most of the times. But there are some times that there are steps greater than 1 level. As I have been told, it is due the truncation of the routine to maximice the speed and not accuracity of the gaussian blur, and to the low bit deph used to calculate the result.

 

>You should not be able to see
>that. I doubt it's a PS problem. You must be right that it is a monitor
>problem. I wish I could try it on a digital video LCD display.

Yes. Those little steps are revealed throught the monitor's limits, but there are some cases that the steps are generated by PS (Vicent Peris has more experience about this...he has a good eye to catch that artifacts).

 

 

Regards,

 

Carlos

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