Automatically adding alt tags for images

So since being W3C compliant is supposed to help with search optimization I've always wanted to be able to automatically add alt tags to images that don't have them. Since alot of the content on our websites is entered via a cms, we don't always have complete control over this.

I've seen regular expressions that are supposed to detect img tags without alt tags in them, but couldn't get this to work the way I wanted it to.

I think I've found a good solution to this. I'm just using regular expressions to find all image tags, then going through a list of them, finding ones without alt tags, and then trying to process the src tag to come up with a guess as to what a good choice for the alt tag would be.

Here it is, remember you've got to have (using System.Text.RegularExpressions;) at the top of the cs file

fixalt.txt

Dynamic recrop of images

So this e-commerce site I'm doing has thousands of images. Some unfortunately were non-square and then placed centered on a white background, even if the predominant colors were darker. Going through all of these would be a nightmare production task.

I wondered if I could programmatically detect these rectangular white regions, and replace them with a better chosen color. The problem is that some of the images are really on a white background, centered and shouldn't be touched.

I've written some code that comes in diagonally until it detects a pixel that isn't white is the next pixel. I then check a vertical and horizontal line from that point. If one direction is all white, I assume that it is a rectangular region. Same from the bottom right corner coming up.

If one of these checks fail in both directions I bail. If I detect different orientations on the top and the bottom I bail. But if I detect horizontal or vertical stripes of white I then step in one pixel from all four "corners" and then average the color values. I then use this color to fill the white regions.

I know that certain shapes (peanut like) can screw up this calculation. Still the color chosen for the fill in that circumstance will be decent (and only fill white regions). Also some of the images have dithered edges, possibly throwing off the calculation. Still this seems to work pretty well.

Click here to see what I'm talking about. The first three images are a diagram of how the code looks at various images. The next items are the full size image, image resized (with border) without this dynamic cropping applied, and image resized with dynamic cropping applied.