Mitch Bain: Your digital camera and JPEG work flow
In a previous article I noted that I always use the JPEG format even though my camera boasts a RAW capability. JPEG is a lossy compression format, some of the picture information is lost; unlike RAW where all the pixels are delivered to your graphics editor. Here we will look at JPEG in more detail.
When you open a JPEG picture in a viewer or editor, the program decompresses the picture displaying all the pixels as best it can. If you notice blocky looking color or jagged edges, where you expect to see smooth color and smooth edges, then you are observing JPEG artifacts, a consequence of lossy compression. JPEG artifacts can be expected because of the options you chose when you set up the camera. Lots of compression results in small file sizes and noticeable artifacts.
But suppose that you programmed the camera for high quality and minimal compression, but you still encounter JPEG artifacts. The problem may well be that your computer work flow is at fault.
To visualize how this happens let’s say you just got back from vacation with a memory card full of great photographs. You load the photos into your computer and you start scanning them with a viewer such as Windows Picture and Fax Viewer. No harm so far. Then you notice that the photo of Uncle Ned’s barn has this car off to the side that spoils the shot. You open your editor (later articles will discuss editors) and crop the car out of the photo and save it as “UncleNedsBarn.jpg”. That action causes you to lose some photo quality. You look at Uncle Ned’s barn again and decide that it needs to be straightened. You open your editor, straighten the barn and save the changes. Bingo you lose some more quality.
The image of Uncle Ned’s barn has now undergone three compressions. Once in the camera when the originally JPEG file was created and again on each of the two subsequent edits. If you open other pictures in an editor (not a viewer) and do even minimal editing and save as JPEG files you have decreased the quality an imperceptible bit each time. Do this enough times, while ignoring the JPEG quality settings, and here comes the dreaded artifacts.
Consider this: Back in the film camera days if you wanted copies of a snapshot, you could either take the snapshot itself or the negative back to the drugstore for additional copies. Which method gave you the highest quality? The negative for sure, and that’s why you should take care to keep the negatives.
Here’s my recommended work flow:
Treat the original image files from the camera as you would negatives. Don’t lose them. Copy them to the computer, look at them in a viewer delete the losers, rename and organize and archive them to a hard drive or DVD. Don’t do any edits and saves.
Now the pictures are in three places (the camera’s memory chip, the computer and the archive) so feel free to delete the camera’s files by formatting (erasing) the chip in the camera.
You may now open your graphics editor and have at it knowing you can always revert back to the original if needed. It should be noted that some graphics editors, such as Picasa2, are diligent about not overwriting the original file. Many editors such, as PhotoShop Elements, have a native format that does not compress the image and the native file can be re-opened many times for further editing.
Finally when you are done you may save the final edit as a JPEG. For example edited JPEG files are appropriate for e-mail attachments and slide shows.
The advantage of this work flow should be obvious. The picture is compressed to JPEG no more than twice-once from the camera and only once more from the editor.
Mitch Bain is a Volunteer with the Gold Country Computer Learning Center. Our website is http://www.gcclc.org. For information about computer classes call 273-0497. Email Mitch with your questions at email@example.com
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