< HDRI & Panoramas
> Evil Flaws
> HDRI Pictures
— HDRI: Tone-mapping —
Tone-mapping can be compared to the adjustment of brightness, contrast
and gamma for conventional LDRI (Low Dynamic Range Image)
pictures. However, different tone-mapping operators come with many more controls.
There are global and local operators. Global operators work on the whole picture
while local ones also adjust the particularly bright or dark parts without changing
the rest of the picture considerably. At the time being, I am aware of the following
- Adaptive Logarithmic, global; 5 parameters.
- Ashikhmin, global; 3 parameters. After Michael Ashikhmin.
- Cipher, local; 10 parameters.
- Display, global; 7 parameters.
- Drago, global; 2 parameters. After Frédéric Drago.
- Durand, global; 4 parameters. After Frédo Durand.
- EriKate, local; 4 parameters. After Erik Reinhard und Kate Devling.
- ExpLog, global; 0 parameters: Exponential oder Logarithmical.
- Exponential, global; 8 parameters.
- Fattal, local; 10 parameters. After Raanan Fattal.
- Greg, global; 1 parameter. After Greg Ward.
- Linear, global; 0 parameters.
- Lock05, local; 10 parameters. After Thomas Lock.
- Lock06, local; 10 parameters. After Thomas Lock.
- Mantiuk, global; 3 parameters. After Rafal Mantiuk.
- Pattanaik, local; 6 parameters. After Sumanta Pattanaik.
- Photoreceptor, global; 9 parameters. Approach to film response.
- Photoreceptor Physiology, global; 5 parameters.
- Reinhard, global; 7 parameters. After Erik Reinhard.
- Scan, global; 0 parameters. Francesco Banterle.
- Schlick, local; 10 parameters. After Christophe Schlick.
- Stockham, local; 10 parameters. After T.G. Stockham.
After Erik Reinhard
After Erik Reinhard und Kate Devling
After T.G. Stockham
After Raanan Fattal
||Both Reinhards and Stockham are near the reality, Fattal
is dramatised. All tone-mappings show the full brightness range: the light from the
window and the fluorescent lamps are not «burned-out» and even the dark
places are not completely black. The picture on top right was tone-mapped in HDRShop
with one of Banterle's plugins, the other three in Artizen HDR 2.5.14.
The top left image is nearest to reality but it appears bland, poor in contrast and
therefore a bit foggy. The one on top right is pleasingly bright, also down the
corridor, but gives the impression of being in a hospital. Below left features a high
contrast and good illumination. I would choose this picture to advertise for this place.
Below at right finally is far away from reality but it enhances the shadows and gives
this place a dramatic touch. Some parts are brightened up even though no light falls on
them. The picture appears hard and the place unclean.
This is no ranking of tone-mapping operators. You select the tone-mapper according to
the picture at hand and what you want to express with it. Besides, there are so many
parameters to adjust that the result can be fine-tuned to one's desires. There is an
almost infinite number of variations.
<< Mind the detail at left in its original size. The fluorescent tube is
not overexposed and the faint neon light in the light switch still glows. Neither is the
wall blindingly bright as it would be if a flashlight was used. This detail was extracted
from the Stockham tone-mapped picture.
These examples are meant to show the potential of HDRI photography and tone-mapping,
and encourage to start experimenting with it. The effort is well worth it!
This concludes the introduction into the topic but it is not yet exhausted, not at
all. The basics explained here ought to suffice to start experimenting with HDRI