Inverse Karma

Many computer users often hit upon this dilemma – which format to save an image in. The four most popular image formats are – BMP, JPG, PNG and GIF. BMP can be imagined as some kind of a raw lossless format that is used only in special cases. GIF is largely used for animated images for publishing on the internet (think annoying advertisement banners). But what leaves many of us confused (or ignorant) is the practical differences between JPG and PNG.

JPG is the most common image format. You could call it the MP3 of image formats! Most of the pictures lying around on your hard-disk, your mobile phone, your digital camera – all of them are JPGs. What makes this image format so popular is its high quality – low filesize paradigm. You get great image quality at a file sizes that cannot be offered by any other image format. Notice the two images below. They look almost identical, but look at the striking difference in filesize of the two formats. But there’s a catch. The JPG algorithm takes into consideration how the human brain conceives images. When there is a lot of visual information to process (The clouds, the lake, the trees, the bench, the people), each pixel is only relative to the next and so a JPG image can lose a lot of pixel-detail and instead focus on simply producing a visually realistic reproduction.

Now notice the two sets of images below. At first glance, the two image are identical. But if you take a close look at the gray background and Elisha’s lips, you’ll notice colour irregularities in the JPG image. These are called artifacts, caused by approximation of the JPG algorithm (remember, JPG excels in images with a lot of visual information). The PNG, although 15 times bigger in filesize, faithfully reproduces the original colours and edges of the image. Still, JPG seems a better choice because of its small filesize, considering the fact that most people cannot notice such nuances of an image at first glance.

PNG is most suited for what is called line art – images with sharp lines, like cartoons. So if your image contains a lot of text or lines and sharp edges, PNG is the suitable format. Notice the artifacts in the JPG below – the pink trail left by the butterfly (seen clearly in the PNG) is almost ineligible.

Another important feature that JPG lacks inherently is support for transparency. The JPG when saved, substitutes a colour (mostly white) for the transparency in the original image. However, the PNG retains the transparency. See the PNG image where the region surrounding the pie-chart is transparent – that is, it shows the underlying page’s colour.

So remember, if you’re gonna print a family portrait or a photograph of you standing at the beach, choose JPG. If you’re scanning a hand-sketch or your own cartoon or if you’re saving an image with lots of text and/or transparency, go for PNG.

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