Mine eyes - a saving test

[John Reidy]

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

[Mike McCarty]

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]

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]

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?

[Hanna Larsson]

(English is not my first language, but I think you will get the picture... )

Reducing pixels and reducing resolution can be the same thing. 2000 x 3008 could be the "pixel size" of an image. Resolution tells you how these pixels are displayed/placed. Were you to show this image in all its actual pixels on a screen with 72 ppi it would be 27,8 x 41,8 inches in size. If you change resolution, but keep the "pixel size" the original amount of pixels the image consists of, the parameter that is changed is the size in inches. At res. 300 the size will be 6,7 x 10 inches, and still 2000 x 3008 pixels.

For printing (real printing) an image and get good quality it should be res. 300. Then your total amount of pixels constrain you in how large print you can get, in inches. Increasing the resulution in the computer without porportional reduction in size will not give an image of higher resolution in reality. The information in the exsisting pixels will just be spread out on some more pixels. But likewise, an image isn't any better, regardless of it's massive amount of pixels, than the information saved in these pixels. A digital camera can have all the pixels in the world, but poor optics and not good enough techniqe to fill these pixels with useful information.

I don't know if I've written anything you didn't already know and I would gladly be of further assistance if you think I can help you, or anyone else for that matter...

[Mike McCarty]

Hanna,

How can you know so much yet be so far away?

Thanks for that, I think I understand it better now.

Do you have an opinion regarding my saving test above?

Do you think that even though the many savings of the JPEG file didn't seem to reduce the quality of what we see on the screen, would you expect negative consequences to show up when the file is printed?

[Hanna Larsson]

Your test was very interesting since I've heared the same thing as you through the years, "do not save your images in .jpg, or they will be gradually ruined". It leaves me puzzled...

When saving, were you asked to choose quality level? And if so, what did you choose? I suppose you took the best possible alternative, but anyway? Maybe the fenomenon is only apparent in a specific program?

As I've understood it .jpg takes away information that we don't see when displayed on a screen. Smart for sharing images, if you don't compress them too much, but since the file gets smaller, something must get lost? I think they get simplyfied and that subtle nuances dissapear first. Although my screen is set on displaying "true color" I doubt it really does, so maybe we all should see a diffence if the images vere printed. If the print is good that is...

How did your image files change in size? (kB) That would be very interesting to know...