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Old Jan 11, 2007, 12:51 AM   #1
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Camera: CX7525

I have a question about the jpg's that my camera records. When I transfer pictures to the computer and immediately re-save them, with the editor's compression set to the very minimum, the file size increases quite a bit. Does this mean there is quite a bit of in-camera compression when the pictures are recorded?
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Old Jan 11, 2007, 2:50 AM   #2
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denrub wrote:
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Camera: CX7525

I have a question about the jpg's that my camera records. When I transfer pictures to the computer and immediately re-save them, with the editor's compression set to the very minimum, the file size increases quite a bit. Does this mean there is quite a bit of in-camera compression when the pictures are recorded?
Yes it does. Very few cameras use an extremely high quality compression like quality 12 in Photoshop or 100% in Irfanview. Most are higher than Kodak though. And some cameras with a "super fine" quality are close to Photoshop quality 11.

I would add that it does no good to immediately resave them at higher quality. The JPG files that come from the camera are as good as they are going to be and saving those files at higher quality accomplishes nothing but add another compression. Always keep the JPGs as they come from the camera as your digital negatives. When you edit, resize etc you should "Save as" with a different file name or to a different folder so you don't affect your digital negatives.
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Old Jan 11, 2007, 8:26 AM   #3
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Thanks, you don't know how long I've been looking for an answer to that question. I assume that in-camera compression level is a fairly important factor in a camera's performance (for larger prints), but Kodak doesn't list it in their specs, and I couldn't find anything about it anywhere. For future reference, how do I find out about compression levels in different cameras?

Thanks again.
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Old Jan 11, 2007, 2:00 PM   #4
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The best way is to look at Steve's sample photos. He gives the file size. From that you can come pretty close to determining the compression. And you can compare different cameras with the same Mp to get a comparative idea of the compression. Steve's samples from JPG cameras are at highest quality.

You can also download one of the photos and save it at various qualities to see what compression it is using by comparing the file sizes.

The compression on your Kodak isn't that bad. You might see some slight difference in a large print or pick up some very slight compression artifacts viewing 100% where you have to scroll around to see the whole image. What you absolutely don't want to do is "Save" rather than "Save as' with most editors and viewers. Most will save at the same quality as it was opened with. You will probably pick up artifacts with the second save. You best bet is to save in the proprietary file type like PSD for Photoshop or a loseless format like PNG or TIFF. If you have a requirement to save as a JPG use the highest quality unless you are reducing it for web viewing. Make sure to not alter your original JPG.

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Old Jan 11, 2007, 5:12 PM   #5
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So far, all my editing has been for the Web but I want to get into the printing end of it soon. First, though, I wanted to archive all my originals properly, but before I could do that, I needed to get this file size/compression straightened out so I could archive at the best quality.

I have to admit that I did re-save a few groups of originals at lowest compression, but then wondered about that since the original information is supposedly lost for good with the first compression, so I stopped until I could find out more about it. But I did know enough to save the edited pictures as a different file, so I at least got something right.

Thanks, you've been extremely helpful. I can get on with my archiving now. Much appreciated.
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Old Jan 12, 2007, 1:48 PM   #6
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Greetings Derub,

When you capture an image with your digital camera, there is a lot going in the background. Essentially each pixel captures a reference in what is known as color space which is then turned into a mathematical reference. All of these are then combined using an algorithm and combined to form your image. It is quite a feat of technology and math. How the algorithm is written is the key and there are many ways that this could be done.

Since it takes quite a bit of time to perfect such processes they are regarded as intellectual property and rarely ever shared on public sites. So, the best thing to do is to use the standard formats in which the resulting data is provided (files from your camera).

I suspect the issue that you want to understand is resolution and how that impacts your images, i.e. printing, on the web, in your camera and so on. One of the leading people around that I know of today is Andrew Rodney. For details on Resolution try visiting his site at the following URL. It will give you some insight into what you want to know. I have found him and his work quite worthwhile. Look for the reference to Resolution (you have to scroll down a bit).

http://www.digitaldog.net/tips/index.shtml

Talk to you soon or see you around the forum.

Ron Baird
Eastman Kodak Company

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Old Jan 12, 2007, 5:25 PM   #7
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Hi Ron. Yes, once I found that re-saving the originals resulted in larger file sizes, I questioned the quality of the originals. I guess I had assumed that cameras would record jpg's at the best quality possible, with the least compression, but obviously that's not the case. Now that I know, it seems that the level of compression would be an important criterion in a camera (for me, anyway; maybe most point-and-shoot users wouldn't care). I understand the issue with intellectual property, but would the whole process be given away if the level of compression was given? (I'm just asking out of ignorance again.)

I had a quick look at the link you gave and it does look good. Thanks for that, and for the info.
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