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Old Nov 14, 2002, 10:38 AM   #1
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I took pics with an Olynpus D490 at SHQ JPG. The files are about 1.2 megs. I recently took a pic and printed it after some editing in Microsoft Picture It. I printed an 8x10 on generic photo paper on a HP 720 and it came out great. I then saved the changes. Then I got a new printer HP PhotoSmart 7350 took the same file and printed it on HP photo paper and it came out even better. But I noticed that the file size is now only 230 kbytes about 1/5 th of the original file size. This I assume was do to saving it in Picture it. I am suprised that I didn't lose any quality on the picture. I thought the bigger the file the better the quality. Can someone explain to me how file compression affects the picture.
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Old Nov 14, 2002, 11:43 AM   #2
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What sort of picture was it? A pic with little detail and flat areas of colour might well be very easy to save to a higher compression level without significant loss. Try some garden scenes printed at 10X8 and see if you get the same result!

Exclude the printers and paper from your question first, by comparing the same (detailed) areas of your compressed files at high zoom on a monitor. I'd expect you to see a difference.

If this is not translated to the print, then the printer rather than the camera is making your pictures! Sometimes we see 'quality' as picture brightness and contrast with vivid colour, rather than pics representing the natural scene with high detail - printer manufacturers are aware of this.
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Old Nov 14, 2002, 12:16 PM   #3
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This was a picture of 5 12 year olds in very bright bathing suits covered with shaving cream at night outside with auto flash. Even the flesh tones come out great and the colors are incredible on both prints.
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Old Nov 15, 2002, 3:31 AM   #4
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I use 'Picture It' as well...when you 'save your picture as', and select 'jpeg', there is an 'options' box that appears...if you click this box, you can change the quality (file size) (compression) and save the pic at it's original size...or you can save it as a 'tiff' and lose nothing, again, look for the 'options' button.
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Old Nov 15, 2002, 6:50 PM   #5
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There are several things going on here. For JPEG images, file size is basically determined by two things, resolution (number of pixels) and amount of compression.

If you sized the image for printing, it is possible that PictureIT reduced the resolution in the process. You can look at the image properties. Assuming that you shot in SHQ or HQ mode on the D490, the image should be 1600 x 1200. I have a feeling that you will find that the resolution hasn't changed. To me, 1.2 Meg seems like a pretty large file for a 2 MPixel image, so I'm guessing that they don't compress the images very much. That leads us to:

JPEG is a "lossy" format. It is very good at omitting information when you save and then interpolating data when you reload in a way that isn't very noticeable to your eye. Chances are that when you saved the image in PictureIT, it was more highly compressed and that accounts for the difference. I don't remember how it works in PictureIT, but most programs allow you to modify the compression quality. The higher the compression the lower the quality and the smaller the file. The change in printers or other characteristics (as voxmagna mentioned) may account for the perceived change in quality.

An important thing to notice is this. Because JPEG is "lossy", every time you save a JPEG image you lose a little something. When you load the image from disk it gets uncompressed and then when you save it, it gets recompressed (and more quality is lost). This loss is additive! If you open a picture and save it over and over, it can get progressively worse and worse. This is why I recommend that you should ALWAYS archive your original images before you edit. That way, if the quality starts to be noticeably worse, you can return to the original and start over. Also, don't save the image unless you have made changes.

In your case, since you are still happy with the results AND you file is smaller, you win. Don't count on that happening every time though.

I have the beginnings of a web page on some of these issues. It is very incomplete at this point, but you can take a look here:

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