Downsampling & HDRI builds

[Marsu42]

Reading the im docs it appears I need a hdri-enabled build to use the extended downsampling methods - it says "Remember to use HDRI with such -resize filters": http://www.imagemagick.org/Usage/filter ... downsample

1. The context of this warning isn't specific, is it just about Cosine/Ginseng/... or also for LanczosRadius?

2. Is a hdri build "necessary" or just "recommended" (and what's the tradeoff)?

3. Does a hdri build have any connection to the quantum depth (q8/q16)?

4. The Windows compiles (http://www.imagemagick.org/download/binaries/) don't seem to be hdri enabled, I tried the x64 dll im6 versions?

Thanks for enlightening me, this is all rather confusing for poor /me

[fmw42]

I am not a windows user, but I think you may get better results in HDRI mode, but you can still use -resize (advanced methods) without it. HDRI is not connected to the Q level compile. You can compile at any Q level, though I recommend Q16. But I believe you have to install manually to get HDRI enabled. I do not think there are any precompiled HDRI versions for Windows on IM 6. However, if you want to try the IM 7 beta, it comes by default in HDRI as per the suggested of Nicolas Robidoux, who developed many of the advanced sigmoidal and gamma -resize and -distort resize methods. If you do not need those advanced methods, then I do not believe you need HDRI. Part of the issue was that -sigmoidal-contrast results go outside the range of normal non-hdri compiles an so he wanted the IM 7 to be HDRI by default.

see also viewtopic.php?f=22&t=25935

One of the windows users or someone using those methods can comment further and correct me.

[snibgo]

Fred is correct: the pre-built v6 Windows binaries are not HDRI. V7 is.

I haven't experimented enough with different resizing filters to say how much HDRI (or a larger Q number) is needed.

Building IM on Windows, with Cygwn tools, is quite simple. Instructions on my site.

[Marsu42]

Thanks for your answers!

However, if you want to try the IM 7 beta,

I did try it now and then but came to the conclusion that until it's declared "replacement ready" for im6 scripts, it's too much hassle trying to figure out what im7 doesn't do like im6 so my scripts fail. I'm a big fan of the im7 unified approach though and hope it'll be ready before 2020 :->

Building IM on Windows, with Cygwn tools, is quite simple. Instructions on my site.

Yeah, I already did it myself a few times - but after decades of looking at compiler outputs and config options, there comes a time in a man's life you simply just want to use the stuff instead of tracking and updating various required dependencies (cygwin doesn't have 'em all in their repo)

[snibgo]

Yeah, I already did it myself a few times - but after decades of looking at compiler outputs and config options, there comes a time in a man's life you simply just want to use the stuff instead of tracking and updating various required dependencies (cygwin doesn't have 'em all in their repo)

Agreed. I mostly use the pre-built binary, and use my home-built version only when I need Q32, HDRI, process modules, or other customisation.