HDR stitching

From Autopano

1 HDR-Stitching - sample 1

HDR-Stitching - sample 1

Step 1 - Stitching

First, you need the pictures. You can get the picture for this sample here [[1]]

Unzip the package and make a panorama detection on the pictures (You can do this quickly by right clicking on the folder and select Detect Panorama).

You'll get that panorama :

Step 2 - HDRI Color Correction

As pictures have a big exposure difference, we use the HDR color correction. So hit the HDR color correction button : Template:Soft ressources:editor:color hdr.png

During some seconds, it calculates the correction and then display this :

My screen is too bright ! **Don't panic** : that's normal. Here's the explaination. When switching to HDR mode, pixels value change meaning. In standard mode, it's a standard RGB float value. But in HDR mode, the float value can have a greater dynamic than in standard mode. That's exactly what HDR means : High Dynamic Range.

The issue we have here is simple : we have float values ( pixels color of the panorama ) ranging from 0.0001 to 1,000,000 in common scene and we want to display them on a device using integer values [0..255]. Every float value from 0.0001 to 0.999999 will be 0 as integer, every pixel greater than 256, will get a 255 integer value. Your screen cannot display directly HDR values.

Step 3 - Playing with HDR Level

So what ? We can start to play with the HDR Level : Template:Soft ressources:editor:histogramme hdr.png

Just use this tool to see what's happening. Here's a movie illustrating that :

Image:Tutorial-hdr1-slider.swf?668x517

This HDR level tool adjust the window of value that are displayed on the screen. So you can see that even in overexposed area, pixels are consistent by moving the slider. The float value is good but cannot be displayer easily.

Step 4 - Tone Mapper

The solution ? Tone Mappers.

Tone Mappers are filters that help you to remap the huge dynamic of the scene to a standard range [0..255]. Autopano Pro already provides two tone mappers but much more are planned to be added soon.

So go to the filter menu and activate Tone Mapper RH02.

Don't forget to click on enable to switch the mapper on. We use this technic to allow two tone mapper dialog boxes to be open at the same time. So we can switch quickly from one to another just by hitting one button.

Here's a result with the given value for Tone Mapper RH02 :

The panorama is now equally exposed from dark areas to bright areas.

Step 5 - Levels

Last step is to play with levels. Our level tool is build upon float values too. So you have a far more precise control with it than with a standard level.