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Previously we discussed the evils of applying interpolation to your image and the benefits of minimizing the amount of interpolation. Here I would like to visit a similar related topic and that is Compression, and where we want to avoid it and particularly if you're trying to maintain maximum image quality. What we have on screen here is two images. The one on the left is saved out as a . PSD, a native Photoshop file coming right from a RAW file, no compression. On the right is another version of this file. It's saved out instead of .PSD as a level 4 JPEG, so fair amount of JPEG compression has been applied to.
When you look at these two images, as you can see here we're looking at them at 100%, the image quality is fairly similar although the more you look in some of the details here you can see that this doesn't have quite as much detail. But you know what at a cursory inspection both images look okay. So you know maybe saving it out as JPEG is not so bad. But now let's zoom in and let's take both images up so we're comparing exactly the same view to 250%. We'll take the one on the right to 250 as well, and let's orient them just about the same on the screen and now look at there detail.
Couple of different places here, take a look at down in this area where you have the big indent in through here and compare the same area, see how broken up. You can see these blocks of pixels that are created by the JPEG compression. What's going on here is that this is a lossy type of compression which means that data in the image is averaged and then re-created so you end up with losing a lot of sharpness and a lot of detail in your image. And look along this one vein here and up in this area where you see lots of fine detail, all of that detail is completely lost up in here because of the JPEG compression. Now if you're viewing this on screen at 100%, in particularly even smaller, not a big deal, if you're printing to a low-quality printing device doesn't show up nearly as much.
But when you're printing to high-quality devices that really do show the detail, such as a very high-quality inkjet printer or a commercial printing press you're really going to see the differences in image quality, sharpness, and detail. In addition to avoiding interpolation we want to avoid compression as much as possible if you want to maintain maximum image quality.
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