Am 05.08.2017 um 06:28 schrieb Kenneth:
> "Kenneth" <kdw### [at] gmailcom> wrote:
>> One more image test, again for my own purposes: This PNG is *directly* from
>> POV-Ray (and NOT post-processed in Photoshop.) If it shows up correctly here
>> both as a small preview AND as the larger hi-rez image, then the problem will be
>> in my use of Photoshop, for some strange reason. An interesting experiment...
> 
> Confirmed(!) THIS PNG image looks correct to me--both the small preview as
> well as the larger hi-rez version, when clicking on the preview.

... and this one carries not only a `gAMA` chunk indicating an encoding
gamma of 1/2.2, but also a `sRGB` chunk indicating that in fact the
encoding doesn't use a gamma-law function but rather the sRGB transfer
function.

> This is indeed strange-- but at least I now have a clue as to what might be
> going on, within Photoshop (and how it treats POV-Ray-generated PNG
> renders--possibly changing their gamma when I certainly wasn't expecting that.)
> I need to test this further.
> 
> However...this does NOT explain the difference in appearance here of my
> originally posted PNG's-- the previews vs. the hi-rez versions. The only
> possible explanation I can come up with is that the newsgroup 'previews' are at
> one gamma setting, while the hi-rez versions are shown with a different setting.
> Sounds a bit crazy, I know...

The previews are most certainly generated without worrying too much
about gamma, effectively generating a JPEG image gamma pre-corrected for
whatever would have been the decoding gamma of the PNG file (4.4 in your
case).

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Am 05.08.2017 um 21:29 schrieb Kenneth:

> I also downloaded my own original PNG image post (the one shown in these
> screenshots), and it appears correct in *all* of my various image-viewer apps,
> no gamma change.

Then you should ditch all your various image-viewer apps, as they all
seem to disregard the PNG file specification regarding gamma.

Get LILYsoft's IC, which is the best image viewer/converter for Windows
I've seen so far. OpenEXR and Radiance HDR support included, and written
by POV-Ray community member "Ive".

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Am 05.08.2017 um 23:27 schrieb Kenneth:

> SO... it seems that my use of Photoshop-- at its *typical* gamma setting of
> 2.2-- was introducing a gamma change into the POV-Ray PNG image. I have aways
> assumed 2.2 to be the correct gamma in PS, for any/all PNG images that I've
> downloaded from the 'net, and even for Photoshop-created PNG images. But it's
> NOT correct for post-processing a POV-Ray PNG render: a PS gamma of 1.0 is
> necessary (at least for both of the newsgroup's two preview sizes to show up
> correctly!) So, *something* is amiss somewhere-- either a flaw in my version of
> Photoshop, OR in how the newsgroups treat preview images.

Have you made your display gamma known to Photoshop?
(And what version are you using anyway?)

> By the way, these are my POV-Ray render settings:
> A) assumed_gamma 1.0 in the scene file
> B) Display_Gamma of 'srgb' in my .ini file
> C) File_Gamma of 'srgb' in my .ini file

Good boy. That should be exactly right... provided you have set up your
display and Windows to match sRGB gamma.

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Am 09.08.2017 um 03:30 schrieb Kenneth:
> Another view. No fog this time, but with radiosity (using the defaults, with
> brightness .6. I haven't yet worked out the best rad settings for this kind of
> scene... OR for an animated moving-camera version, which is even more
> demanding.)

Radiosity brightness .6 is unrealistic. If brightness 1.0 gives you too
bright indirectly-lit areas, your pigment*diffuse values are too high.

The only physically legitimate reason for using brightness is to set it
/above/ 1.0 when using a low recursion limit, to counteract the
resulting dimming in comparison to high recursion limit renders.

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Am 09.08.2017 um 22:46 schrieb Kenneth:
> Thomas de Groot <tho### [at] degrootorg> wrote:
> 
>>
>> This is really good indeed. A building tycoon would lick his lips and
>> wring his hands seeing all that beautiful building space wasted on low
>> buildings ;-)
> 
> Ha! True enough. (I can think of one such real-estate tycoon here in the U.S.;
> TRUMP TOWER would *never* have been built with only 3 storeys!)
> 
> I need a somewhat better 'algorithm' than a simple power-law, to restrict the
> number of really tall buildings in my cityscape; I don't want to wipe out the
> middle scales at the same time. I need to think on this awhile...

Gaussian-ish distribution, maybe?

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Am 09.08.2017 um 09:00 schrieb Thomas de Groot:
> On 9-8-2017 4:12, Kenneth wrote:
>> Stephen <mca### [at] aolcom> wrote:
>>
>>>
>>> Fire and fury is in vogue. ATM
>>>
>> Funny thing: I just now saw that belicose Trump statement on the BBC--
>> I was too
>> busy building my little city to take note of today's world events. ;-)
>> N. Korea
>> has some nutty leadership... but so does the U.S!! Like two little
>> bully-boys
>> daring each other to a fight in the schoolyard... with nuclear
>> weapons. My

>>
> 
> That image has imposed itself on me too I am sad to say.

I must say that I find it rather comforting that in this reboot of the
Cold War franchise the country I live in does /not/ have /the/ front row
seat for a change.

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On 20/08/2017 20:50, clipka wrote:
> Am 05.08.2017 um 21:29 schrieb Kenneth:
> 
>> I also downloaded my own original PNG image post (the one shown in these
>> screenshots), and it appears correct in *all* of my various image-viewer apps,
>> no gamma change.
> 
> Then you should ditch all your various image-viewer apps, as they all
> seem to disregard the PNG file specification regarding gamma.
> 
> Get LILYsoft's IC, which is the best image viewer/converter for Windows
> I've seen so far. OpenEXR and Radiance HDR support included, and written
> by POV-Ray community member "Ive".
> 

Seconded

-- 

Regards
     Stephen

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On 21-8-2017 1:43, Stephen wrote:
> On 20/08/2017 20:50, clipka wrote:
>> Am 05.08.2017 um 21:29 schrieb Kenneth:
>>
>>> I also downloaded my own original PNG image post (the one shown in these
>>> screenshots), and it appears correct in *all* of my various 
>>> image-viewer apps,
>>> no gamma change.
>>
>> Then you should ditch all your various image-viewer apps, as they all
>> seem to disregard the PNG file specification regarding gamma.
>>
>> Get LILYsoft's IC, which is the best image viewer/converter for Windows
>> I've seen so far. OpenEXR and Radiance HDR support included, and written
>> by POV-Ray community member "Ive".
>>
> 
> Seconded
> 

Terced

-- 
Thomas

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On 20-8-2017 22:32, clipka wrote:
> Am 09.08.2017 um 09:00 schrieb Thomas de Groot:
>> On 9-8-2017 4:12, Kenneth wrote:
>>> Stephen <mca### [at] aolcom> wrote:
>>>
>>>>
>>>> Fire and fury is in vogue. ATM
>>>>
>>> Funny thing: I just now saw that belicose Trump statement on the BBC--
>>> I was too
>>> busy building my little city to take note of today's world events. ;-)
>>> N. Korea
>>> has some nutty leadership... but so does the U.S!! Like two little
>>> bully-boys
>>> daring each other to a fight in the schoolyard... with nuclear
>>> weapons. My

>>>
>>
>> That image has imposed itself on me too I am sad to say.
> 
> I must say that I find it rather comforting that in this reboot of the
> Cold War franchise the country I live in does /not/ have /the/ front row
> seat for a change.
> 

Agreed. Neither was our second row seat, I mus say... I still remember 
the cruise missiles business.

-- 
Thomas

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clipka <ano### [at] anonymousorg> wrote:
> Am 05.08.2017 um 04:12 schrieb Kenneth:
> > I just noticed something strange about the PNG images I posted: When I look at
> > the small *preview* images here in my post (using the latest version of
> > Firefox), they look correct...
> > But when I click on the image previews here-- and the higher-resolution
> > versions appear-- the gamma of the images isn't correct! They look
> > darker, with more contrast.

>
> My bet is that you instead have a wonky post-processing workflow, as
> your PNG file is seriously odd: The `gAMA` chunk in your PNG file claims
> that the file was encoded with a gamma of 0.22727 = 1/4.4 (or
> "pre-corrected for a display gamma of 4.4", as it would be called in
> other file formats), rather than the typical 0.45455 = 1/2.2; I suspect
> that `gAMA` chunk is outright wrong.

Agreed, without reservation ;-) I have no clue as to why my (older v5.0) of
Photoshop would create such an *extremely* wrong gamma encoding. I knew it was
somewhat wonky (from reading about its possible PNG problems years ago)--but not
to that degree!
>
>
> For the JPEG file format, as far as gamma goes there's only a W3C
> recommendation for use on the internet. The file format itself is
> blissfully unaware of gamma. So you just have to pray that the target
> system /happens/ to interpret them in the way you intended them to be
> interpreted.

I assumed that just about all relatively recent flat-panel monitors are
factory-preset gamma-wise to show JPEGs correctly. I guess that has always been
my own rather dubious 'benchmark' for using JPEG vs. PNG. (And I'm coming to
realize that my own doubts about PNG actually owe their origin to my crappy
version of Photoshop! I've been using it WAY past its 'expiration date'. But the
'pain' of dealing with PNGs there is hard to forget.)

I now understand the newsgroup 'problem' I encountered with my
originally-uploaded Photoshop'd PNG file--that crazy gamma 4.4 image: The
'small' preview in the newsgroup is modified (for want of a better term) to look
'correct' no matter what it's gamma might be (or when there's no intrinsic gamma
at all, in the case of JPEGs); whereas the 'larger' preview (the much darker
one, in my case) shows the ACTUAL/awful gamma encoding of my image. And I was
assuming the opposite!

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