Mine eyes - a saving test

[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...

[Mike McCarty]

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?

When I save it does not ask me specifically if I want to select a quality level. I must have made that choice before I select to save. Therefore the images remained at 200 resolution throughout.

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

The bird photo in it's unaltered state was 1.54 MB
The bird photo after being saved 25 times, full image was 1.54 MB

The boat photo in it's unaltered state was 982 KB
The boat photo after being saved 25 times, full image was 981 KB

I tried something else here:

The first is the unaltered, the second saved 20 times.

I took the leaf that was unaltered other than having been cropped to forum size. I then took this smaller file and saved it 20 times. I thought that if it started with much less information it might make a difference.

The file started and ended at 41.1 KB

[Hanna Larsson]

I tried saving a jpg in Photoshop. I didn't get a quality question then, only when I chose "save as" a .jpg. And what the question is about is how much compression to do. No change in resolution, just in simplification.

I must do some similar testing as you and see what my results are. I will not have time to do that until tomorrow, but I'll let you know how it turnes out.

The fact that your images are the same size suggests that our eyes are telling the thruth, that they haven't changed...?

[Hanna Larsson]

I did a quick test now saving an image 20 times AS a jpg. I chose maximum quality every time and as far as I can see nothing changed. The image looks the same and is the same size.

The first image is the one saved 20 times.