Re: [APML] Fw: images

[Chuck Vaughn <aa6g@aa6g.org>]

Hi Carlos,

>   
> >In practicality, the finest grain films are limited to about 5
> >- 6 bits and most color films are about 4 - 5 bits.
> Here is where I desagree with you. Due the nature of the film media I 
> am convinced that we have more colors (or gray steps) than 6 bits.

I'll repeat what I said before. 6 bits per channel is 262,144 possible 
colors. You won't see the difference between that many and 16.7 million 
possible colors in any one image.

>  For all practical ways a photograph of a continuom gray gradient 
> indeed looks continuos... and the human eye needs a little more of 
> 7bits to see that.

That's probably true in viewing the real world but not a monitor or a 
print.

> Anyway, due the human eye's limitations, the scanning process, the 
> monitos, etc. I think that you have a strong bias in your medition... 
> that makes appear the film's "bit deph" worse than it is.

Perhaps, but compare my 10 bit image example to any astrophoto.

> Just a final thought... if film can handle only 5-6 bits, why do we 
> have 16bits scanners? Why not just 8bits ones?

Marketing! Sorry, I couldn't help but be cynical. ;-) Really though, my 
old SprintScan 35ES which scans in 10 bits and outputs in 8 bit is 
quite adequate except the Dmax it can handle isn't high enough.

> PS: Photoshop is a nasty program... as Vicent said, it destroys the 
> data. I don't trust the ways it works. Just make a gaussian blur, 
> you'll see steps in the gradients.

I tried it. I made a continuous gradient from black to white and 
performed a guassian blur. No steps here. It is very smooth at any 
pixel setting of the blur.

> Also there is a problem with the monitor's capabilities of displaying 
> the data. Even if you have a continuos (at >16bits) gradient you'll 
> see some steps.

No monitor I know of is capable of displaying 16 bit grayscale. As I 
said above, I have no steps in a continuous gradient. Maybe you have a 
hardware problem?

Chuck

_______________________________________________
Astro-Photo mailing list
Astro-Photo@seds.org
http://seds.org/mailman/listinfo/astro-photo