Mine eyes - a saving test

Mike McCarty · 01-12-2005, 11:04 AM

Mine eyes have seen the glory of the coming of the Lord. Actually, I don't think they have, or if they did, they didn't know how to interpret it.

I get curious about the oddest things. I took three photographs each produced thusly:

Nikon D70, ISO 200, JPEG-Fine-Large, each 3008 x 2000 pixels. This is the largest JPEG file produced by the D70.

Each began the test as a virgin file. Each was then saved 25 times (not in photo shop but a wannabe). Each was then cropped to 400 x 600 pixels. I then resized the original image to 400 x 600.

The program would not allow me to save the file unless I had actually altered it in some way. So each time I made an indistinguishable mark before saving.

Each of the large images below are only resized to 400 x 600 and otherwise untouched (except for the one save to resize). The first cropped image represents the virgin file after it was saved 25 times and then cropped to what you see. The second cropped image is the virgin file cropped and saved once.

Mike McCarty · 01-12-2005, 11:07 AM

Next image ...

Mike McCarty · 01-12-2005, 11:09 AM

And the third and final ...

John Reidy · 01-12-2005, 09:46 PM

Incredible (I mean it's really neat - not unbelievable).

The differences on my screen @72 dpi are nearly if not impossible to see. Is the same true at your higher resolution?

I purchased the camera and 2 lenses from a camera store in NY and won't receive it until next week. I am still expecting to buy an additional card (1G 40x) and a remote. I can hardly wait to start experimenting.

Mike McCarty · 01-12-2005, 10:10 PM

Maybe there is some part of this that I don't grasp. I have always heard that saving JPEG images would eventually sap the life out of them. They continue to be compressed and have data thrown out after each successive save.

So I wanted to see just how far from perfect I could go. You would think that the example above, after being saved twenty five times would show more signs of wear, but I don't see it. Especially after cropping down as far as I did.

I have destroyed many an image, but it has been through the over manipulation of something that started out being poorly exposed. It would seem that only the act of saving a JPEG that was properly exposed does not create the kind of deterioration that I expected to see.

If someone can point out how I have misunderstood this issue I would like to hear it.

Mike McCarty · 01-12-2005, 10:16 PM

It would have been interesting to see a RAW image as part of the control group. I would guess that the quality of the image would be noticably better at the tight crop.

John Reidy · 01-12-2005, 11:08 PM

I don't know, Mike. The answer might lie in the higher resolutions when trying to print.

Mike McCarty · 01-13-2005, 12:10 AM

Quote:

It would seem that only the act of saving a JPEG that was properly exposed does not create the kind of deterioration that I expected to see

I think what I said above doesn't make good sense. It has to be true that the saving program doesn't no beans about whether the image is properly exposed or not. It just saves whatever it finds and lets mine eyes determine if it is proper. But, the point is still the same.

You might be right John, maybe if I took the harshly saved image to the printer I might see a difference, but I don't see why really. If I get ambitious I might try it.

I also don't understand the "resolution" thing anymore. When I worked in film the only way I could get my image into the computer was to scan the hard copy. At the time of scanning I would select a resolution. This had a real impact on the quality of the image. Now, when I check the resolution of my digital images they all say 200 no matter what. I suppose if I change that number to the down side I would start loosing something, but I can't imagine having a positive impact by increasing that number after the fact. I thought maybe the ISO had something to do with resolution because I shot most of my stuff at 200. But that ain't it, the image below was shot at 800 ISO and it still shows 200 resolution.

John Reidy · 01-13-2005, 03:11 AM

Mike-

You are correct about increasing the resolution would have no effect. You would have to lower the size of the image to gain a higher resolution. Example, you have a 24"x18" image @ 200 dpi. To increase the resolution you would decrease the size ( say to 12"x9") and then raise the dpi (say 300). This would give you more pixels per inch and consequently more information per inch.

Mike McCarty · 01-13-2005, 10:45 AM

Quote:

This would give you more pixels per inch and consequently more information per inch.

Wouldn't this begin to give a different, computer created, look? It seems to me that anytime information gets moved, crowded, separated, that that begins to take the image away from it's origin.

What of this example: I have a large file, too large to post on the forum. I need to reduce the file size so I reduce the pixels from 2000 x 3008 to 400 x 600. In doing so I have created a less sharp image. Could this effectively be done by reducing the resolution. Wouldn't this reduce the file size as well? I don't understand the difference between reducing resolution and reducing pixel size. Why would I ever reduce resolution if I can just reduce the pixels?