In order to get a higher dynamic range
you can blend multiple differently exposed images. The easiest way to do
so is to average all of them. However, the resulting image usually suffers
from low detail contrast and looks dull. On the other hand, we can preserve
detail contrast while compressing overall contrast by using blurred masks,
gradient enhanced masks or -even better- with the smart blurred masks.
The basic idea is to combine the images
using only shadows and midtones. We create a blurred mask for each image
with a curve mapping highlights to black and mid tones and shadows to white.
The background image is of course not to be masked.
This mask should be blurred for smooth
gradients and small details in order to prevent their contrast, but leave
hard edges intact, where the contrast can be reduced savely. For this purpose
the desaturated copy of the image is treated with the smart blur filter
and then inverted. See Manually step by step HowTo
for more information on this technique.
The details of the individual processing
steps are contained in six Photoshop-actions. Two can be used in droplets
or batch processing, two to add images manually, and two to change between
the mask modes.
The simple 'Blur Mask' and 'Gradient Mask'
actions are no longer part of the package. They did not yield very good
results. For version 1.3 I refined the settings for the actions called
'Smart Blur big' and 'Smart Blur small' for big images that will be reduced
in size later and for small images that won't be reduced. Version 1.3 actions
are now compatible to photoshop CS 16 bit layers.
Many thanks to John from http://www.sandiego360.com
who permitted me to use his images. The originals
are available. They where shot to stitch a spherical panorama. On the
following pages you find higher compressed but equally sized copies.
Images
1/6s
1/3s
0.7s
1.5s
3s
6s
10s
20s
Results
This images cover the whole contrast a monitor
can display. Be sure to have your monitor adjusted correctly. You should
see a dark gray area with an even darker frame in the black furniture.
The averaged result
is dull and too bright for the outside scene.
The unadjusted smart
blurred (small) version shows good contrast and exposure for the outside
scene but the shadows are too bright.
The output of the
'Smart Blur big' action shows pixelated edges visible in the pictures on
the wall or the sofa.
The layer opacity
of the smart blurred version were adjusted individually to get a better
result. From top to bottom (light to dark) the layers got this opacities:
20%, 30%, 15%, 50%, 50%, 50%, 50% (only the top three layers where adjusted).
Tutorial
The contrast blending actions can help you
a lot, but you still have to find the right way of using them, since the
default values sometimes don't work very good. I have written this tutorial
to help you find a workflow which leads to satisfactory results.I assume
you have first experiences with the actions and some images to work with.
You can take the images above if you want, but I suggest you shoot your
own. You'll learn easier by solving your own problems ;-)
First open the darkest
image in Photoshop. Then use the actions to apply the other images starting
with the next lighter and ending with the lightest. You should end up with
the darkest image as background and layers from the darker at the bottom
to the lighter at the top. (Note that you can reorder layers in the layer
palette by dragging them)
The resulting image
is a bit dull and too bright for the interior.
Now start at the
top switching layers off until the remaining scene appears to have good
contrast. In our example switching off the top three layers make the outside
scene look pretty good.
By switching the
layers on again, we can see which layer is responsible for dulling the
result. Here layer 5 makes it significantly duller.
Carefully reduce
layer opacity until the result looks good again. Always try to optimize
the brightest areas that are affected by this layer. Here the opacity is
reduced to 15% to increase contrast for the objects on the balcony.
Proceed to the top
layer by layer. Be careful not to dull previously better parts and not
to make areas lighter than they should be in reality. However, you should
try to use the maximum opacity that still gives a tolerable result. In
the example layer 6 affects the interior shadows. It could be set to 30%.
If you set the layer
opacitiy too high, darker parts in the
image may become too light. Consider two
areas from the scene, the walls and the shadows in the corners. If you
set the layer opacity to a very high value, the shadows may become even
brighter than the walls. In our example a value of 20% would be good.
In images where you have smooth gradients
from very dark to very light all layers can be adjusted to have the resulting
gradient smooth again.
The result shows
tolerable good contrast in all parts of the image. Dark areas stay dark
and light ones are light but not over-exposed.
images
