Best sharpen settings for multiple image sizes

[xfactor]

I am running an automated process via a VB script and the IMage Magick COM+ library that processes thousands of images a day for web based viewing.

The program takes a source image and resizes it from the initial size (Usually 600x600 or larger) into various smaller sizes (The exact sizes depend on the specific site configuration, this is usually in the range of 500x500, 355x355, 135x135 and 60x60 or something similar).

I am not an image processing expert, so I was wondering if anyone out there is familiar with the best sharpen settings for this sort of scenario. I am currently using "-adaptive-sharpen" with a value of "0" and while the larger images (500x500 range) are ok, the smaller images are coming out really blurry.

Does anyone out there have experience with optimizing sharpening settings, and if so what would the best settings be in your opinion? I can set the sharpen values dynamically at run time if this needs to be optimized on a per size basis.

I tried using "-unsharp" with a value of 0 as well, but it's making the larger images too jagged.

My current command string looks like this:

"-thumbnail", (xxxxx), "-adaptive_sharpen", "0", "-colorspace", "RGB", "-flatten"

Any help is greatly appreciated.

[fmw42]

you may be better off with more flexibility using -adaptive-sharpening 0xsigma and adjust the sigma. If you use just radius=0, sigma is fixed at 1 and you may need a smaller sigma.

[xfactor]

I tried this with "-adaptive-sharpen", "0x0.5" and "0x0.2" but it's just not turning out decent quality for the smaller sizes (135x135 is especially bad...Smaller than that and it's too small to be noticeable anyway).

[fmw42]

what about larger sigmas?

can you post links to examples?

why are you converting to colorspace rgb at the end and not the beginning?

[xfactor]

I am getting slightly better results with "-adaptive-sharpen", "0x0.6'. Higher sigmas (2, 4 even 6) didn't help at all.

Processing speed is absolutely key for what I am doing, so I thought that the color conversion might be faster on the smaller resized image. I don't know if it really makes any difference or not. Does the order of color conversion affect quality?

I can't upload examples at the moment, but will see about it tonight.

[fmw42]

-adaptive-resize

Do you mean -adaptive-sharpen?

You could also try either -sharpen or -unsharp

[xfactor]

Yes. I edited the above post to correct that.

I tried -sharpen and -unsharp, but neither of them worked as well as -adaptive-sharpen.

-unsharp definitely has some potential, but it seems to work a little too well for what I'm doing. The images output are sharp to the point of looking jagged in certain areas. These are mostly thumbnail type product images, so I prefer to keep them a little softer. I haven't played with modifying the parameters as much as I should, but from reading around, everyone seems to have the best luck with -adaptive-sharpen.