| Why you should not work with saved and resaved .jpg files and a major problem with shooting .jpg images.
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1. Taking pictures in the .jpg mode can render what is known as jpeg artifacts in your image. These are small, white or lighter colored spots, often along edges of things like flower stems, but can be seen in any area of the pic. Many, many pictures are taken in .jpg mode and look great, no problem at all.
If you are serious about a very important shot, use your camera's .raw, .tif or its own uncompressed format. Yes, this will consume huge portions of your media and hugely reduce the amount of pictures before you can download to your pc or change the CD in your camera.
If you prefer not to work in the camera's factory, uncompressed format or the .tif, you may prefer to work with Photoshop's .psd, PaintShop Pro's .psp, a Windows Bitmap (.bmp) or some other uncompressed format. Immediately convert your uncompressed image to the desired, uncompressed format of your image software or Windows' .bmp (uncompressed) format. Compressed images will degrade as the next point will exlain.
If you do shoot in the .jpg format, immediately convert to an uncompressed format in your pc for ALL of your editing work. You should never use .jpg until you are ready for a final output.
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2. A .jpg image may look great in your editing software when first captured from your camera, scanner, etc. Then you save it as a .jpg. Let's call it Hibiscus.jpg.
Later, when you decide to work Hibiscus.jpg and you load it from your hard drive or other media to your editing software, you will have a degraded image. At first blush, it may not appear so. If you enlarge the ratio of the onscreen view so that you see individual pixels nicely, you will see that there are inconsistencies of colors and detail. It seems to be worse with colors; but alas, colors are what determine detail.
After you work with Hibiscus.jpg and overwrite your image, or you play it smart and save it as Hibiscus_2.jpg, you have saved a degraded image.
Then, should you desire to make more modifications, or you simply open it to view, you will see the degredation is worse than last time. Should you overwrite your original, you've really taken a loss.
Therefore, it is best, with camera in hand, if you are going to do some serious, artistic work, that you do not shoot in .jpg mode. THEN, after your images are in your computer, they should be saved in a safe, uncompressed format and everytime you open and modify the images, save them with a new name, such as adding "_1" or "_01" or "_02." That way you never lose your original. Then, when you're ready to add it to your screen saver folder, post on the internet, email to someone, add to your digital picture frame or iPod, then you can output your latest modification as a .jpg and it will be okay.
Yes, the person viewing your images from the internet site or your email will get a slightly degraded image, but it won't be enough to concern yourself with.
We should be grateful to Fotki for allowng .png images. They do better than .jpg if it is your intent for the viewer to get a more pristine display.
Should the bottom fall out and someone steals your .jpg image and it comes to a dispute, your original, uncompressed file, or even your .bmp file will prove better than the thief's copy.
Jpeg artifacts only come from a digital camera. Once they're in your computer, you will not create these little pests.
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Below are some examples. With the collage images, you may not see the severity of degredation unless you click the Original Upload link and when the image opens in new tab/window, enlarge to full size. The degraded image will be very discernable.
I hope this helps.
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