High Dynamic Range tutorial:What is the maximum file size that I can work with?

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What is the maximum file size that I can work with?
How to do HDR:The file size to consider for Photomatix is the size expressed in number of pixels, i.e. width X height. Since Photomatix has to decompress the images for processing, the compression factor of the input images does not make any difference in the ability to process large files.
The maximum file size (in number of pixels) that you can process with Photomatix depends on the following:
· the RAM your computer has
· whether your OS is 32 or 64-bit
· the pixel depth of your images
· the number of bracketed photos you are combining
· the number of other memory-hungry applications opened on your computer
· the free space available on your hard drive
· the processing mode (i.e. whether you are running Photomatix Pro in batch mode or from the interface)
Additionally, it is important to note that there is an upper limit to the amount of RAM that is made available to applications like Photomatix. On Windows XP 32-bit, this limit is as low as 2 GB, regardless of your RAM. That is, it will still be 2 GB via virtual memory if you computer has less than 2 GB RAM, but it won’t be more than 2 GB if your computer has 4 GB RAM (unless you enable the /3GB switch).
Then, external memory fragmentation further limits the memory available to Photomatix, by making it impossible to allocate a contiguous block of memory large enough to contain the whole images data. External memory fragmentation is a problem on Windows OS, and particularly on Windows XP. It means that the system does not organize the available memory efficiently, making it unable to re-use the memory that Photomatix has released.
When combining large source images, please use Batch Processing available from the Automate menu.
When you create a large HDR image file that you want to tone map in Photomatix Pro, you will have to save the HDR image in the Radiance format (.hdr extension) to avoid out-of-memory issues.
For an idea of the memory necessary to process your images, the following formulae give a rough estimate of the amount of memory needed (in bytes)
For Tone Mapping with Details Enhancer an HDR image file opened in preview mode or using the batch:
width * height * 18
For the method Fusion/Adjust in batch mode:
width * height * 3 * ((bit-depth/8) * numberOfImages + 1.5)
This means that tone mapping a 50 MegaPixels HDR image using Details Enhancer in preview mode requires around:
50,000,000 * 18 = 900 MB
And fusing three 50 MegaPixels 16-bit images with Fusion/Adjust requires around:
50,000,000 * 3 * (3*2 + 1.5) = 1,125 MB
For “Generate HDR”, the amount of memory is almost the same as for Fusion/Adjust, which can be quite high when the source images are in 16 bits/channel mode and/or when there are many of them.
High Dynamic Range tutorial:However, there is an option in Batch Processing that avoids memory limitation by creating the HDR image file one strip at a time, provided the source images are TIFF files. When this option is checked, Photomatix Pro will only load, process and write a given number of rows from the source images instead of the entire images. This way, you can create an HDR image stored in Radiance (.hdr) format from any number of large source images, even on a computer with limited RAM.

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