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LDR / HDR - Workflow case B

From LDR input with bracketing to LDR output

This is the case that photographers called HDR: several exposures in input and LDR panorama in output. It's classic for virtual tours but also for landscape photography, etc...
(LDR : Low Dynamic Range | HDR : High Dynamic Range)


Workflow

The idea to get through such panorama is first to group images by layers, then to use the color correction by layer (ie by exposure level) to adjust the exposure between the images within the same layer.
The anti-ghost is also active in each layer. Then, the fusion will preserve the best exposed areas from each layer.

Example 1

Source images

In this first example, we use the test images from the Freeman's book.

Autopano250 HDR-casB-ex1-sources.jpg

Import and stack images

Import all your photos in Autopano, a group is created. Here we have 21 images, 7 brackets of 3 different shots. If your images are not automatically stacked you need to select all your photos in the group, then right click to open the contextual menu and select the option "Create stacks by N". Choose the "Number of pictures per stack", 7 in this case. You also have to choose the "Index of the main picture" (this is the picture used for the control points detection, see below).


Importing and stacking your images.

Note: using a well exposed bracket is important too as Autopano will not be able to find accurate points in low and high exposures, where the images are generally not really detailled. The reference image will define the exposure where Autopano will calculate the control points to link the images.

Detection

Open the Group settings, in Detection tab check the option "Use hard links" (for a stack). Then you can launch the detection.

AUTOPANO LDR TUTO 5 - Detection settings.jpg

Settings

Open the panorama editor. To get a preview of the fusion, you only need to enable it on the fusion tool.

AUTOPANO LDR TUTO - 8 - Fusion & adjustements HD.gif

Now you can adjust the fusion settings "Exposure target", "Dark enhancement" and "Light enhancement" to your convenience as shown in the animation above.
For the brightest areas of the scene (the lights!) the information used comes from the under-exposed brackets; and for the darkest areas, the information has been taken in the highest exposures.

Render

In the Render settings, use the Exposure Fusion preset.
You should know that if the fusion has not been enabled in the editor but that the Exposure Fusion preset is used on the rendering, the default settings of the fusion are used (targeting an average exposure).
As illustrated below you can choose whether to export the different layers (corresponding to each bracket level) or just the result of the fusion.

AUTOPANO LDR TUTO 11 - Render with and without layers.gif

We can also note that in the fusion's case, it was useless to shoot too many brackets. Very underexposed images did not contribute to the final result. This is not necessarily applicable in the case of an HDR output where the aim is not to choose the pixels from the best exposures but to combine information from different exposures (this is only possible if the dynamic range of the rendering format is really HDR).

Example 2

Source images

This example is similar to the previous case, but more like the bracketed shootings made ​​by the majority of users.
That means less exposure levels (3 levels here) and an automatic reference exposure (brackets levels are not identical).

Autopano250 HDR-casB-ex2-sources.jpg

Settings

The settings are almost similar to the previous case too. But as the brackets don't get the same reference exposure levels, the result of the blending can be locally unbalanced.
To avoid this, we increase the Multiband blending level.

Multiband blending level from -5 to 0.

Generally, increasing the Multiband blending level allows multiband rebalance the final rendering.
However, if the level is too high, the final result can be a bit "flattened". So it needs to increase this level only if necessary.

Example 3

Source images

Some scenes don't need to be fully bracketed. In this example, the ambient light is fairly balanced except for the shot of the bay window.
We thus only brackets the shot of the bay window.

Autopano250 HDR-casB-ex3-sources.jpg

Settings

We must check that both bracketed pictures have been added in different layers to avoid the LDR color correction to deal on these images (color correction must be set by layers).

Note : if the main layer is well balanced, it is not necessary to enable the color correction.

Autopano250 HDR-casB-ex3-groupes-en.jpg

You must use the Exposure Fusion preset. The fusion will be apply only where different exposure images are located.

Render

The fusion has preserved more matter in over-exposed area of the bay window.

Result using the same exposure images
Result using the bracketed images





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