What InterpolationMode and CompositingQuality to use when generating thumbnails via System.Drawing

re: What InterpolationMode and CompositingQuality to use when generating thumbnails via System.Drawing

nathanaeljones — Thu, 09 Oct 2008 21:57:35 GMT

Cool! I recently read the article, but hadn't realized you wrote it.

I usually have my photos in the same directory with the .aspx file that contain them, so putting everything in a photos folder would be a severe disadvantage... I like relative paths :).

MapPath completely ignores the security and access settings in the URL authorization portion of web.config. Since that's the easiest way to protect static files, it's nice to support it. Integrating as HttpHandler makes that compatibility automatic.

I also use a *wide* variety of thumbnail sizes, so having them all the same wouldn't benefit me much. I often need several versions of the same file, so the caching system needs to be that flexible also.

I also implemented automatic cache management to prevent denial of service attacks... you can read my comment at nathanaeljones.com/.../asp-net-image-resizer

re: What InterpolationMode and CompositingQuality to use when generating thumbnails via System.Drawing

Bertrand Le Roy — Thu, 09 Oct 2008 21:08:33 GMT

@Nathanael: well, yes, I also wrote this, which explains how to do the same thing:

weblogs.asp.net/.../generating-thumbnails-in-asp-net-dotnetslackers.aspx

re: What InterpolationMode and CompositingQuality to use when generating thumbnails via System.Drawing

nathanaeljones — Thu, 09 Oct 2008 20:49:41 GMT

You might be interested in this image resizing module, then.

It integrates with the pipeline, so you can just slap a query string onto any image URL to get it resized or converted:

image.jpg?thumbnail=jpg&maxwidth=30

It also permanently caches resized versions to disk... otherwise you run into serious scalability issues. With disk caching it's practical to use this on high-load production servers.

Take a look:

nathanaeljones.com/.../asp-net-image-resizer

Image Capture and Auto-Resize With Cropper

Mike Ormond's Blog — Fri, 06 Jun 2008 10:46:59 GMT

Having talked about the pain of capturing image snapshots , someone mentioned Cropper and its plug-in

re: What InterpolationMode and CompositingQuality to use when generating thumbnails via System.Drawing

Thomas — Thu, 27 Dec 2007 00:09:08 GMT

can someone please post a code sample on how to do this resizing using the Paint.net api, I downloaded the source code and it's an abyss of functions that are not documented and don't even bother posting on their forum so far they've been less than helpful.

I'd truly appreciate it.

thanks

re: What InterpolationMode and CompositingQuality to use when generating thumbnails via System.Drawing

Bertrand Le Roy — Wed, 12 Dec 2007 01:59:06 GMT

Rick: thanks for the info! Cheers!

re: What InterpolationMode and CompositingQuality to use when generating thumbnails via System.Drawing

Rick Brewster — Wed, 12 Dec 2007 01:27:58 GMT

Paint.NET uses its own code for resampling. There are issues with the underlying GDI+ library when trying to use some of System.Drawing's interpolation modes. It quite often makes the border pixels slightly transparent. Or it makes things blurry like you documented here.

re: What InterpolationMode and CompositingQuality to use when generating thumbnails via System.Drawing

Bertrand Le Roy — Mon, 10 Dec 2007 19:27:54 GMT

Lionel, that is very good info. Thanks a lot.

re: What InterpolationMode and CompositingQuality to use when generating thumbnails via System.Drawing

Lionel — Mon, 10 Dec 2007 17:04:20 GMT

Actually, you can get nearly the same result as Photoshop's "Bicubic sharper" using Paint.NET. Here is the method:

1. Apply a Gaussian blur (with radius 2)

2. Resize using Best Quality/Supersampling (to 134x100 pixels)

3. Apply a "Sharpen" effect (with radius 2).

The Gaussian blur avoids moiré patterns, and the final sharpening increases the _apparent_ sharpness of the image (see en.wikipedia.org/.../Unsharp_masking for how it works). Both would be rather easy to implement in a standalone assembly.

The visual effect is nice, but the is some cheating involved: even if it looks nicer, the blur+sharpening actually further degrades the image.

As for Lanczos resampling and other high order methods, it looks like they are much more suited to encreasing the resolution of the image. For making small thumbnails, it looks like very little is gained.

re: What InterpolationMode and CompositingQuality to use when generating thumbnails via System.Drawing

Bertrand Le Roy — Thu, 06 Dec 2007 23:23:00 GMT

My point exactly, Morten, although the differences between the compressed versions are still very visible. But there are only 24 hours a day and those will have to wait a bit.