Alain Martel <kua### [at] videotronca> wrote:

> >
> > Here's a (hopefully) corrected JPEG version.
> >
>
> Do you mean that you set POV-Ray to save the image as a JPEG ? By
> default, it saves the images as PNG.
>

No, the 2nd image I uploaded (JPEG) was made by taking my original saved PNG
image (assembled in my old Photoshop v5), re-loading it into PS, and re-saving
it as JPEG. I trust PS to at least do *that* accurately ;-)  The original
POV-ray renders were PNG files.

[Btw, I use Windows 7, with a "system default sRGB" ICC color profile.]

> The PNG version look good here. (Mozilla Thunderbird) Maybe the
> application that you use to show the posted image don't handle PNG gamma
> chunk properly.

The basic problem is that my old Photoshop apparently saves PNG files with a
*very* wrong embedded gamma-- 4.4 (!) (I should have known better, and checked
my PNG image in Ive's IC/Lilysoft viewer app before uploading it; his is the
only app I have that shows the *true* embedded gamma of the image.) ALL of my
other viewer apps automatically correct(??) the gamma when presenting the
image-- which I truly don't understand. In older newsgroup posts, I've read
various comments that say something like, "A PNG image will appear correct in
any viewing app". So perhaps my nutty version of Photoshop embeds a gamma value
when it should not embed anything at all?

It is interesing that Thunderbird shows my uploaded PNG image as 'looking
correct', like my other apps do; whereas the newsgroup webpage I use shows the
bad (but *actually* correct) 4.4 embedded gamma. Apparently, the newsgroup page
is a more 'strict' interpreter of the actual image gamma-- like Ive's IC app.
But which situation is actually  correct, as to expected PNG-viewing behavior?
That has always been a mystery to me, even on my own computer. Are all of my
other apps wrong when they 'correct' for bad gamma? Or are they doing what they
are supposed to do?

Obviously, I need a better version of Photoshop. But it's such a workhorse app
for me that I don't want to change it (or to pay Adobe's monthly usage fees.) So
I *usually* stick to making JPEGs with it, not PNGs.

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