Would someone explain this to me please?

Why if I use the same camera and lens with the quality of the picture in the camera not changed do the size of the files of my pictures vary so drastically? Sometimes there is a 2 or 3 meg difference. Jeff

Captured images vary due to content and image complexity. Because of this the file size can also vary widely. It has to do with the way the image is digitally captured and written to memory.

It's because you're using JPEG format.
Jpeg is a lossy compression, and the less detail the smaller the file.
So lots of sky, or dark night, or distant grass - smaller file as it has no detail in it.
Closeups filled with detail will give larger files.

I appreciate both of you taking the time to explain what was going on.

I do have a follow up question. If I take a picture in JPEG can I save it as raw changes can be made and then save it back as JPEG and not loose anything? Jeff

You'll have lost the information already with the original JPEG conversion in the camera, but if you save that file as a RAW in your favorite editing program, you can edit non-destructively until you next output to JPEG, where compression will take place again.

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Originally Posted by Grandpaw

If I take a picture in JPEG can I save it as raw changes can be made and then save it back as JPEG and not loose anything? Jeff

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You probably can't save in RAW.
You can use TIFF while you are editing, there should be an option to turn off compression, or set it to lossless only in the Tagged Image File Format dialog.

Quote:

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Originally Posted by Grandpaw

I appreciate both of you taking the time to explain what was going on.

I do have a follow up question. If I take a picture in JPEG can I save it as raw changes can be made and then save it back as JPEG and not loose anything? Jeff

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Check the menu settings in you camera. There my be a setting for TIFF or other type of loss less file format. But be aware your storage requirements will increase at least 20 times. But the cost of storage is very cheap now. I got a couple 4Gig cards at Costco two weeks ago for less than a hundred.

Jeff,

Don't know if this helps

I always save my edits as PSD or pspimage files which are lossless formats and these formats keep all the layers you may create during the edits. If I am going to print or send to somone or post then they get saved as JPG. I always keep the layers so that I can make slight modifications later if someone sees an issue with the image.

RAW is camera dependant and so you cannot save as RAW. Not all camera's can save as RAW.

Roger

A Photoshop Raw format is available in Photoshop, but it’s not the same format used in camera raw image files. The Photoshop Raw format (.raw) is a flexible file format for transferring images between applications and computer platforms. In that respect, it's much the same as the TIFF format- though the TIFF format is more popular.

- Joe U.