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mike Member
Joined: 09 Jul 2004 Posts: 6401 | TRs | Pics Location: SJIsl |
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mike
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Fri Dec 09, 2016 4:13 pm
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It's not a hypothesis, it's math. but I will see if I can do an example.
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osprey Member
Joined: 14 Aug 2010 Posts: 47 | TRs | Pics Location: Issaquah |
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osprey
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Fri Dec 09, 2016 6:21 pm
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jpeg is a compressed file format. While the image will stay the same dimensions in width and height, every time you save a jpeg file, it compresses the image. You can think of it as averaging the colors of adjacent pixels, but it's more sophisticated than that. You are making a trade-off between file size and image quality - the smaller the file size, the lower the image quality. For some images and compression levels, it's hardly noticeable. But for other images, or areas in an image, you will get noticeable artifacts. But as Mike says, it just math - the smaller file has less information left in it.
And jpeg is not round-trip, even at the same compression level. The decompress can't recreate exactly what was originally compressed. If you open a file and save it, will be different than the original. If you open and save it again, it will be different again.
Look at 'jpeg' and 'Lossy compression' on Wikipedia
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mike Member
Joined: 09 Jul 2004 Posts: 6401 | TRs | Pics Location: SJIsl |
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mike
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Fri Dec 09, 2016 6:25 pm
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OK. I can only guess what you were doing with the software but I'm going to speculate that you re-saved the files at a different compression rate and stripped the exif and thumb to get the smaller size. This may be the default setting for your software. In any event it doesn't appear that you "looked under the hood" so I'm only guessing.
So this is what I did. I took this photo:
... and cropped and applied different jpg compression levels to give you an idea of what is happening. First crop is of the original 16bit tiff file. Then a jpg compression of 85 and finally 40. These numbers are arbitrary and generally run 1-10 and vary depending on the software. Personally I find that around 80-85 is a good compromise between quality and file size.
original rez crop was 272kb 85 jpg 8.9kb 40 jpg 3.6kb
so you can see what happens to the file size. I would suggest downloading Faststone Image viewer (freebie) which has a feature to compare these three images side-by-side.
Bottom line. Just change your camera to output a smaller jpg and don't bother farting around after the fact. And frankly, you're packing way too much camera gear weight for the medium rez jpg's you want. IMHO A good P&S will do as well at a fraction of the weight.
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iron Member
Joined: 10 Aug 2008 Posts: 6392 | TRs | Pics Location: southeast kootenays |
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iron
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Fri Dec 09, 2016 6:26 pm
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mike Member
Joined: 09 Jul 2004 Posts: 6401 | TRs | Pics Location: SJIsl |
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mike
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Fri Dec 09, 2016 6:27 pm
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Tom Admin
Joined: 15 Dec 2001 Posts: 17855 | TRs | Pics
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Tom
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Fri Dec 09, 2016 6:31 pm
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Mike, this is hopeless. Just let iron destroy all his photos in MS paint. As you said, it seems to work for him.
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iron Member
Joined: 10 Aug 2008 Posts: 6392 | TRs | Pics Location: southeast kootenays |
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iron
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Fri Dec 09, 2016 6:35 pm
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mike wrote: | And frankly, you're packing way too much camera gear weight for the medium rez jpg's you want. IMHO A good P&S will do as well at a fraction of the weight. |
shooting baby pics, not mountain pics these days.
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iron Member
Joined: 10 Aug 2008 Posts: 6392 | TRs | Pics Location: southeast kootenays |
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iron
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Fri Dec 09, 2016 6:37 pm
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Tom wrote: | Mike, this is hopeless. Just let iron destroy all his photos in MS paint. As you said, it seems to work for him. |
here's what i'm saying: when i hit "save", i see zero visible change in the photo at a high zoom. i know it's easier to type these messages than to open up the standard, old school photo editing software that every single PC has and try it out on one of the 100000 pics you have, so whatevs.
any answer to automation?
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Tom Admin
Joined: 15 Dec 2001 Posts: 17855 | TRs | Pics
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Tom
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Fri Dec 09, 2016 6:38 pm
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Have you tried lowering JPEG quality in camera? Have you read the manual to see if there are other options to reduce file size?
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iron Member
Joined: 10 Aug 2008 Posts: 6392 | TRs | Pics Location: southeast kootenays |
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iron
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Fri Dec 09, 2016 6:38 pm
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Tom Admin
Joined: 15 Dec 2001 Posts: 17855 | TRs | Pics
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Tom
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Fri Dec 09, 2016 6:43 pm
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Well, why not do that? Much simple solution to your problem is to tell the camera do what you want! It's obviously saving them at higher quality than MS paint.
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Tom Admin
Joined: 15 Dec 2001 Posts: 17855 | TRs | Pics
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Tom
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Fri Dec 09, 2016 6:52 pm
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OK, took me a minute or two to google the D800 manual and find it. I did use MS paint to crop and save the screen print.
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mike Member
Joined: 09 Jul 2004 Posts: 6401 | TRs | Pics Location: SJIsl |
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mike
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Fri Dec 09, 2016 6:55 pm
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Randito Snarky Member
Joined: 27 Jul 2008 Posts: 9514 | TRs | Pics Location: Bellevue at the moment. |
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Randito
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Fri Dec 09, 2016 7:01 pm
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FWIW: The JPEG compression used on cameras is uses a hardware DSP to perform the compression. MS PAINT uses a software method that discards a bit more information.
Reviews of digital cameras numerically measure the JPEG image quality , tweakingirls the parameters to achieve the same level of compression as MS PAINT would lower the numerical score of the image quality.
Anyway I don'the know why the OP would bother farting around trying to save 7MB per image, 2TB drives are pretty cheap these days. BLU-RAY burnable media (25GB each) costs just a buck per disc.
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mike Member
Joined: 09 Jul 2004 Posts: 6401 | TRs | Pics Location: SJIsl |
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mike
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Fri Dec 09, 2016 7:01 pm
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iron wrote: | shooting baby pics, not mountain pics these days. |
Oh yeah, that's right
So I suggest setting your camera to save a "normal" or "basic" jpg + NEF (nikon name for RAW) See the table that Tom posted. That way you can go back and pull up the NEF file to print fairly big. Harddrives are cheap.
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