Focus stacking - why isn't the filesize increasing?

[henrikfoto]

I have been playing a litle with Helicon Focus and wonder about a few things:

1. When you put a lot of pictures together, why aren't the files increasing in size at all?

2. How can this program process a lot of large files this fast? Is any information in the pics
    getting lost in this process?

3. I also wonder if Helicon Focus is the best program for stacking or are there other programs
    that can do this job better? I know PS does it but I have read it's very slow.

Henrik

[theguywitha645d]

The file size does not increase because it has no more pixels nor bit depth.

It is simply comparing contrast at each image and deciding what in each frame is "sharp" and blending those sections together. From what I understand, there is no image loss as you are not adding nor subtracting pixels, just specifying sharp vs. unsharp in the frame. The only loss would be from artifacts added in the stacking process.

Helicon Focus is very good. Whether anything is "better," would be in the eye of the user. Whether others deal with stacking artifacts, except for specialized microscope software, I am not sure. We also use Helicon Focus in our microscope lab and well as Nikon Elements which stacks automatically.

[Bart_van_der_Wolf]

I have been playing a litle with Helicon Focus and wonder about a few things:

1. When you put a lot of pictures together, why aren't the files increasing in size at all?

As said, when the output file has a similar number of pixels and the same bitdepth as the originals, the size will be similar. After alignment and registration, only the higher contrast pixels, or the the ones representing higher spatial frequency detail, from each input image are used. 

2. How can this program process a lot of large files this fast? Is any information in the pics
    getting lost in this process?

The algorithms are quite good in separating the in-focus and the out-of-focus pixels from each focus layer image. The more blurry pixels are discarded.

3. I also wonder if Helicon Focus is the best program for stacking or are there other programs
    that can do this job better? I know PS does it but I have read it's very slow.

IMHO there are three (commercial) obvious candidates at this moment:
1. Photoshop, but it offers no control over the process (unless one pre-masks the individual focus layers), so the output can have artifacts inherent to focus stacking, but no means to influence the output.
2. Helicon Focus, which has the longest track record and performs quite well, and (the pro version) offers built-in retouching, optional Depth map output, and (the Pro version) comes with Helicon Remote for tethered camera and focus control. I've found their support quite responsive.
3. Zerene Stacker, the 'new kid on the block'. But make no mistake, the driving force behind it is a person who is well versed in the focus stacking technology. It offers similar functionality to Helicon focus, minus some of the HF extras.

Cheers,
Bart

[theguywitha645d]

CombineZ is another software and I think ImageJ may also be able to focus stack--ImageJ is freeware.

[hjulenissen]

If you are saving your images as e.g. compressed JPEG at a constant quality, then one might predict minor changes in file-size due to:
1. Sharper edges and more detail (larger file)
2. Less noise (smaller file)

Depending on image conditions, I would guess that either 1 or 2 would dominate the other.

-h