"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.

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...

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On 5-8-2017 4:44, Kenneth 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...
> 

Yes, this is much better indeed, although the original ones posted were 
awesome already. But, not knowing the problem, it was difficult to judge.

Excellent work, Kenneth!

-- 
Thomas

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hi,

On 05/08/2017 00:15, Kenneth wrote:
> Comments and criticisms welcome.

the word, I believe, is "stonking".  :-)  looks fabulous.

my only criticism concerns shape + spacing, the buildings are mostly
(near) square and, as an European who has never visited the US of A, the
spaces between buildings don't quite feel right; for an alternative see
https://www.youtube.com/watch?v=gO9JI7FT1V8, the last 30 minutes or so
(start 5:25:00, no rooftops alas).

cheers, jr.

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"Kenneth" <kdw### [at] gmailcom> wrote:
> With a little bit of fog thrown in-- smog, or city pollution.

This is a nice project, looking good. What happens if the fog is too dense to
see the ground? :)

You could also try to group buildings in blocks, alley-distance apart, with
blocks separated more widely. Maybe vary the height distribution using a
large-scale pigment to select the maxima - you tend to get clusters of tall
buildings in many cities.

[anecdote warning]

I spent quite a bit of time on something similar about a year or so ago, and
it's interesting to see how others approach the same problem differently. I was
making buildings from simple triangle-based boxes, to avoid the textures looking
obvious in close-ups. I then moved on to preparing a city 'plan' by intersecting
street lines to find polygonal blocks, then filling the blocks with buildings
placed very closely together. Both the blocks and the buildings were not
necessarily rectangular. The rooftop furniture was also an issue, and I too
spent a bit of time googling images of Manhattan :)

The block approach proved far too complex and slow for SDL macros, so I moved it
over into a small C++ project with a POV-Ray export to make it more
comprehensible and maintainable. Unfortunately, it's fallen by the wayside for
the time being (stupid real life), but I fully intend to go back to it at some
point!

Keep up the good work.
Bill

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That's really nice.
I think you should also make different photos for the 1st floor of the
buildings. At least to give them an entrance.
Do you plan to add people, vehicles and traffic signs in the street ? It looks
like an endless project ! :-)



"Kenneth" <kdw### [at] gmailcom> wrote:
> With a little bit of fog thrown in-- smog, or city pollution.
>
> Currently, I'm using 16 different window photo-facades, randomly placed on 450
> buildings--each with reflective windows, by way of 'hold-out' mattes and using
> POV-ray's image_pattern feature. (Increasing the number of buildings is trivial;
> but I need to use more photos, as there is already too much window repetition.)
> But I usually make a new photo tile every night!
>
> I've managed to fix four items on my to-do list:
>
> * making sure the windows go all the way to the edges and tops, without being
> randomly chopped off. (I also reworked the window photo images to be more
> accurate 'tiles'-- a learning experience.) The building widths and heights are
> now based on small strict subdivisions of the (larger) tiles-- while still using
> the FULL tile textures on the building. That was a happy accident ;-)
>
> * matching the colors of the 'concrete' edges and tops of the buildings to the
> average color of the photo facades; looks better than plain gray. The architects
> were being creative ;-)
>
> * putting the buildings in a street-grid layout (more or less), so that they no
> longer overlap (well, I haven't *seen* any overlaps yet.) This needs more work--
> as well as to make the streets go in two 90-degree directions, instead of just
> one.
>
> * adding a bit of dirt and aging to the building faces. (The 'dirt' is just an
> overlay of several distorted bumps pigments.) Currently, this is also applied
> over the window areas as well, which I want to eliminate.
>
> Three things I haven't done yet: cleaning up my code(!); trying out POV-Ray's
> new(?) CUBIC pattern for texturing the buildings; and re-working my code to use
> heightfields for the building faces, instead of plain boxes. I hope I can do
> --that-- without a major re-write!
>
> Comments and criticisms welcome.

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> 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: identical to how they appear on my own machine,
> when viewed in either Photoshop or the Windows Photo Viewer. (BTW, I
> post-processed the images in PS, but only to combine two renders into one post.)
> 
> 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.
> 
> Does anyone else notice this? Right now, I have no idea what's going on, or why
> they appear differently on the same website.
> 
> Honestly, I simply don't trust PNG images to show up consistently or correctly,
> anywhere! :-(  I should have posted them as jpegs.
> 
> 
> 
PNG contain gamma information, JPEG don't.
The problem is not the PNG, it's the application used to display them 
that is to blame. Some correctly use the png's gamma chunk and display 
it corrrectly no mather the actual gamma of the device used, other just 
don't.
JPEG don't have any gamma chunk, whitch makes gamma adjustment 
impossible. So, the display becomes dependent on the gamma setting of 
the device used to display it. If that device have the same gamma as 
that of the author, all is fine, otherwise, the image get to dark or to 
light and washed out.
Typically, a JPEG image made on a PC will look washed out on am Mac, and 
one made on a Mac will look to dark on a PC.
When using PNG, it should not be the case. The image should display the 
same on both platforms.

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> 
> 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...
> 

It looks like photoshop is messing up the gamma chunk in some way. Maybe 
it plugs in the actual gamma setting of your system when it need to keep 
the original one.

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Thomas de Groot <tho### [at] degrootorg> wrote:
> On 5-8-2017 4:44, Kenneth wrote:
> >
> > One more image test, again for my own purposes: This PNG is *directly* from
> > POV-Ray (and NOT post-processed in Photoshop.)
>
> Yes, this is much better indeed, although the original ones posted were
> awesome already. But, not knowing the problem, it was difficult to judge.
>
> Excellent work, Kenneth!
>

Thanks, Thomas!

If I seem preoccupied with this image/gamma business, it's because I'm *finally*
close to solving a PNG problem that has been dogging me for years-- specifically
concerning POV-Ray (v3.7xx) PNG renders being post-processed in my (older)
version of Photoshop.

But the newsgroup's PREVIEWS are a different problem. I've attached a screenshot
comparison of my first image post: the visual difference between the newsgroup's
SMALL image preview vs. the larger hi-rez preview-- just to prove that I'm not
imagining it ;-)  (I resized both screenshots to make the comparison easier.)
WHY they should be different is a mystery, above and beyond whatever gamma
mistake I might have made in Photoshop. The two versions should look identical.

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.

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Attachments:
Download 'preview_comparison.jpg' (455 KB)

Preview of image 'preview_comparison.jpg'

Another test-image post-- hopefully my final gamma test... ;-)

This PNG render is post-processed in Photoshop, but I CHANGED my usual 2.2 gamma
there (in PS) to 1.0. *IF* this image shows up correctly here-- in both small
and large previews-- then I will at least have solved the major part of my *own*
problem...

[The thing is, the image looks WRONG in Photoshop with a gamma of 1.0 there--
it's washed out, as I would expect-- but I'll let that pass for now.]

** keeping my fingers crossed **

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Attachments:
Download 'ps_gamma_1_test.png' (1786 KB)

Preview of image 'ps_gamma_1_test.png'

"Kenneth" <kdw### [at] gmailcom> wrote:
> Another test-image post-- hopefully my final gamma test... ;-)
>
> This PNG render is post-processed in Photoshop, but I CHANGED my usual 2.2 gamma
> there (in PS) to 1.0. *IF* this image shows up correctly here-- in both small
> and large previews-- then I will at least have solved the major part of my *own*
> problem...
>

Success!! Both preview sizes here look identical, and correct--well, with maybe
a *very slight* washed-out appearance in both-- but that could be from a number
of reasons on my end, and is unimportant in the bigger scheme of things ;-)

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.

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

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