hi folks,

fun thread, like to jump in. Lots of info, lots of horror, lost of tech detail and still some unanswered questions (like Why is gnomon using tiff (ice-boy)).

JPG is meant to be a publishing format for photograph-like images. When saving the basic image info to JPG you will loose some info on the color hue (which the human eye is not that sensitive for) in favor of gaining info on luminoscity (which the eye is more sensitive for). It's a bit like having floating point numbers first and rounding them to integers when saving. Eg 123.45 becomes 123. When you save at lower quality, the 123.45 becomes 120 or even 100, the rounding just gets more rude.

Indeed, reopening and resaving will load the 123 as 123.0 and save it as 123 again, so after the first loss, no more losses occur (and 100 is loaded as 100.0 and resaved as 100 again).

This changes however when you start working on them. I took the testfile (PNG) as presented by bagginsbill, saved as JPG at high quality (60%), reopend, rotated 90*, saved at 60% again, repeated it a few times and the differences became appearent. Especially the text color was taking the color of the surrounding blue/gray background, and taking Difference blending in Photoshop revealed serious changes overall (after pumping up brightness and contrast to make them visible).

This is why all photographers manuals tell you to use JPG for final publishing only, and not for preliminary and intermediate results in your workflow. On the other hand, when your postwork is limited and you use high quality settings (100%), differences will be minimal, and definitely smaller than the variations between peoples monitor characteristics. And as the chain is as strong as the weakest link, why bother?

A second issue with JPG is that you loose fine detail, sharpness. No real issue for photographic results, but not that good for textures driving displacement, bump, or lace transparency. Still no real issue for images published on the net, but less nice for 7000x5000 images for large scale fine print, or results for the big movie screens. 

A third issue with JPG is that the file format embeds information that compensates for default monitor characteristics. For a long time, Poser failed to take this compensation out of the textures before rendering, but the recent PP2010 has some features to deal with it correctly. Just read the Gamma Correction and P8/PP2010-difference threads about the details. 

A related fourth issue with JPG was that this embedded info was different for Apple and PC. But that one is resolved since OSX / Snow Leopard or so. 

PNG is considered a 'next generation GIF', meant for sharp vector/line drawings. It does not have the limitations of colorhandling as in GIF and does support an alpha channel, but does not support animation. Compared to JPG, the PNG24 does its colortone-handling as good as JPG or even better, but JPG wins on luminosity. Photographers tend to prefer JPG for images with variation and prefer PNG for images with fine color nuances, like monotones, cloudy skies and jungle greens (as far as they prefer JPG or PNG at all).

As PNG keeps the fine details it's preferred over JPG for driving displacements and lace transparency, and everthing else is about the same. It's not the best file format for intermediate results in your workflow, and it embeds monitor compensation. No differences between Apple and PC, but older PNG versions showed different implementations simply causing RGB=(255,0,0) to produce different shades of red between JPG and various PNGs. Thats sort of fixed now. Again, P8 and before did not take out this compensation from the textures before rendering giving you the Poser-look in your images, PP2010 does a better job in this.

Again, all differences are small but for publishing in a Rendo gallery I would prefer JPG over PNG for outdoor Vue / Poser renders and PNG over JPG for sharp fractal images. In all cases, keep in mind that JPG and PNG are meant to produce decent looking results in home, office and other non-graphics-pro environments, like internet galleries and home print.

TIFF is different. It can do 16-bits per channel (so the 123456.789 is rounded to say  123456 instead of 123000), it supports layers and alpha channels, and it does not contain monitor-compensation, and therefore has no difference between Apple and PC. 

This makes it the format of choice for high end print and big screen movie textures (which require 16 bit color anyway), and for high end intermediate results in a professional workflow. mental ray, V-ray and similar renderers assume that any monitor compensation info is taken out of (or absent from) any textures beforehand. Effectively, software like Max and Maya assumes to run in a professional environment anyway, with proper color management implemented at least.

So, have a peek at www.thegnomonworkshop.com. Professional training for artists, it says. Check the software/tools button. No Poser. Gnomon is not into JPG or PNG, unless its for internet publishing or concept print. They're into TIFF instead.

Happy Posing.

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Usually I'm wrong. But to be effective and efficient, I don't need to be correct or accurate.

visit www.aRtBeeWeb.nl (works) or Missing Manuals (tutorials & reviews) - both need an update though