![]() ![]() The LZW algorithm is more than 3 decades old - in 1984 Welch improved the LZ78 by Lempel and Ziv (obviously invented in 1978). To my knowledge, flexiGIF is the first free program to implement both. Instead, I extract the LZW data stream from GIF files and recompress it.įlexiGIF combines two techniques invented by other people - the following ideas are not my original work (I wish they were. and I choose not to play around with image specific optimizations. Unlike the algorithms behind JPEG or PNG, there is is no adjustable compression level in LZ78/LZW compressed data. Keep in mind that flexiGIF's compression is very (!) slow, magnitudes slower than a standard GIF encoder. let flexiGIF optimize the LZW bitstreamįlexiGIF is a command-line tool and can be easily used with custom scripts, etc.run an image-optimizer, such as Gifsicle.There are many sophisticated tools out there, such as ImageMagick, that excel at that job.įlexiGIF is designed to be a tool used after you ran those image-processing programs. Your GIF decoder isn't affected at all - probably it even becomes faster because it has less input to process.įlexiGIF does NOT optimize palette, strip extensions and/or reduces color information. That's several magnitudes slower than other GIF encoders. The only downside: it may takes several seconds or even minutes for a medium-sized GIF image. I'm not aware of any open-source software outperforming flexiGIF. ![]() No visual information is changed and the output is 100% pixel-wise identical to the original file - that's why it's called "lossless optimization".Īnd the results are still GIF files you can open/view with any standard tool. Also, as with any media meant to convey meaning on the web, please make sure you’re including relevant alternative text.FlexiGIF shrinks GIF files by optimizing their compression scheme (LZW algorithm). A page full of gifs can make even a beefy computer or device strain itself, so just because you can bombard your users with animations doesn’t mean that you should (at least, if you care about user experience). The smaller you go, the harder Gifsicle has to work to round everything out in fact, you may find that gifs with smaller dimensions sometimes carry a larger filesize.įinally, I’ll remind you that while gifs can be a lot of fun, they’re not always the best way to convey a message. 500×280 instead of 500×281) tend to resize much cleaner and with less distortion. ![]() In my testing, I’ve found that gifs with even dimensions (e.g. You may also notice that there was some rounding going on, even in my examples. You may have noticed there’s a bit of math involved with resizing images it’s nothing that requires an advanced degree, but it’s still not how I’d like to spend my afternoon. Even if you’re not using WordPress, I’d encourage you to look at the image_resize_dimensions() function and how it’s implemented this is a geometry problem that’s been solved before, so there’s no need to reinvent the wheel. Now that we have the hard-coded version, we’ll break this up into placeholders ( using proper escaping for shell arguments, of course) and we’ll find ourselves with the full, variable-filled version we had before! Gotchas With these numbers at hand, we can ask Gifsicle to resize our image to 267×150: Given the height, we can calculate the width thusly: $src_width / $src_height * $dst_height, or 500 / 281 * 150, which gives us a width of 267px. Confused? Just remember that we have a 16:9 aspect ratio, meaning the height is the smaller dimension and thus cannot end up smaller than 150px or we risk our 150×150 frame not being filled. Now, let’s say we want a square version of that same image, at 150×150. In order to achieve this, we need to perform two operations: resizing the image to fit as much of it as possible into a 150×150 box, then crop off anything outside that area.įortunately, resizing the image is easy: Gifsicle has a -resize option, and the math that led us to our getimagesize()-compatible calculations up above would tell us that to fit a 500×281 image in a 150×150 box, our target dimensions would be 267×150. The original dimensions of this image are 500×281, approximately a 16:9 aspect ratio. Well, that was easy, wasn’t it? In case you’re not well-versed in juggling arguments and using PHP to assemble CLI commands, we’ll apply some real numbers: let’s say we have this gif of America’s Sweetheart, Nick Offerman: ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |