To clarify... if you have not saved the original file, by saving the file as a different name, the changes occur to the file renamed, and are not carried to the original file. [Added] Renaming a file does not change the contents of the photo data; saving it under a different name changes the contents of the file with the new name.

If you do a checksum, there are half a dozen variants, your original file will still have the same checksum as when it was opened. If you save it as the original filename, without alteration, it will have a different checksum and will likely be marginally smaller. This will happen each time you open the file and save it. I don't know if this happens on loading or on saving the file, but, it does happen.

Do this with a *.tif, or *.png (without any compression) and the checksum will stay the same after loading and saving.

It's not a really big problem, but, photographers should be aware of it. Computer users should also be aware that if they save the file, that the quality can be diminished, albeit slowly. You have to exit viewing the file without saving the file, even if you have not made any changes. Other file formats do not have this feature.

Dik

Please point out any errors with references.

Dik

Please point out an error with a reference... the comment is, IMHO, correct.

Dik

Agreed, but, you have to close the files without saving to maintain the same data or if you save it as a different filename; changes to the file then occur under the new filename. Because it's a 'lossy' format, there are artifacts created when you open the file.

Dik

I play engineer for a day job, and, have done a lot of work in restoration of historic buildings. I often encounter brown rot, aka dry-rot. Once encountered, it never gets better; it further deteriorates from its current condition, given the same environment and the structure never improves.

Same with *.jpg photos... they progressively get worse, and, do not improve over time. Often computer users save files without realising that they may be changing them, even, if no changes have been made... it's just a force of habit. It's best that you do not save photos in *.jpg format.

Photos stored in *.png format are not altered, I understand. This format was a compendium of work when it was rumoured that *.gif files were going commercial and a group of graphics programmers came up with the *.png format; a lot of work, effort and thought went in to creating a graphics format that had all the features available. The format was well thought out and has passed 'the test of time'.

The *.jpg was developed for photography and stands for 'Joint Photographic Expert Group', if memory serves. The *.tiff file is lossless as is the *.png and files can be opened, viewed, printed, etc. numerous times without degradation. I just stored about 150 CD/DVDs that go back about 25 or 30 years... ended up with 170,000 files in 11,000 directories; I used a program called FreeFile Sync and it worked like a charm... took care of all duplicates that may have been edited over time. It's an excellent free program for copying/storing files.

Files stored on a CD/DVD don't change with inadvertently saving rather than closing; they are read only. The medium can deteriorate with time, faster, if not properly stored. Best to save to a HDD.

Tiff files are not subject to degradation. The name stands for Tagged Image File Format; I don't know who developed it or why it was developed. The *.tif files are scaleable and are an excellent means of photographic storage. You have to understand that the original photo is the 'best'. It has all the original information directly from the camera. Any modifications or enhancements may improve the appearance, but, the original data is still the 'best'. If you are taking photos for forensic uses, modifying them may render them as non-admissible. Tiff files are a little larger, but, disk space is cheap. [Added] Same with *.png files.

RAW files are the way to save 'good' photos. They have all the unmodified digital data. They can be edited for best effect; modifications should not be saved as the original file name. On a good day, 10% of my photos are good... a real photographer may have a ratio of 50% or 60%. I'm just a technical amateur. For viewing graphics files, there is an excellent viewed and editor, to a lesser extent called Irfanview. This is a fast program that handles a variety of file formats, and it's free. For something more useful for editing photos, there is another free program out there called Paint.Net. This is a Photoshop work alike that has fewer features. I use it often with a plug-in for handling *.pdf formats.

Dik

There's a pretty good 'simple' article at:

https://www.howtogeek.com/285114/how-to-buy-your-first-high-quality-camera/

Dik

I recall a poem from decades back about a man searching for beauty in a field of daffodils... and a line about 'man the enigma'.

Dik

My eyesight is failing, so there's little to be gained from squinting beyond infinity... maybe best to set that as the 'farthest limit'.

Dik

Just because you don't know how space ends, doesn't mean it's infinite.

Dik

Think of infinity as a 'never ending distance/object'. If you can imagine the number of grains of sand on earth, it is not approaching infinite. The earth has a finite volume and a grain of sand has a minimum volume. If you divide the volume of the earth by the volume of a grain of sand, you still have a 'real number'. It is not infinite.

About 30 years ago, we were shopping at the Pickering Town Center looking for a new stove. The salesman jumped right in to help, and explained that the stove had an infinite temperature range. I told him that if we were to live forever, we would never appreciate that feature. He had no clue about what we were talking about.

For cameras, to get back on topic, many camera lenses have a couple of index marks indicating the range of focus for different f-stops. I usually set the upper index mark on the 'infinity' mark so that, for example, for an f-16 aperture, it may be everything from infinity to say 30' is in focus rather than set the focus distance at infinity so that only 60' to infinity is in focus.

Dik

and, with a fast lens, the sweet spot is at a wider lens opening to allow more light.

Dik

I don't know if it's applicable today, but, in times past. A lens with a given speed has a 'sweet' f-stop, generally, a stop or two past the fastest setting where the acuity of the lens is 'best'. For example, an f-1.4 lens may yield the 'sharpest' photos at f-2.8. The resolution chart is used to determine this 'sweet' spot.

Dik

Thanks PixelStan... even better...

Dik

As noted, it would likely be easier to find a pre-printed chart. I used to have one when I was shooting 35mm with my Nikon F2 Photomic... If you cannot locate one, it's possible to draw one using a CAD program if you know the standard line widths. This can be printed using a good laser printer, on a quality paper, at 1200 dpi. It would be helpful to put a couple of lines, say 8" and 10" apart, horizontal and vertical respectively, so that the printed copy can be checked for proper printing scale. Best to try to locate a 'real' chart.

Dik