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04/29/2002 10:12:31 PM · #1 |
Here's another question from a digital newbie...
What causes the files sizes of seemingly identical shots to be so different. While taking pics for the "ground up" challenge I shot maybe 10-12 images that were almost identical in subject, composition, etc,. The only differences were really in slight angle adjustments or maybe a little more zoom or wide angle. I have file sizes that range from 31K to 132K.
For reference, (in case it matters) I have a Sony Mavica FD73 takes a shot that is 640x480.
Also when I saved one pic yesterday (after a slight color enhancement) the size jumped to 246K from 80K- what's up with that???
Anyone care to take a stab at this???
Thanks!
Linda |
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04/29/2002 10:19:44 PM · #2 |
Are the file sizes you mentioned as directly from the camera or after resaving with an image editing program? If it is the latter, it could be that you have the jpeg compression set too high (I know on photodeluxe 3.0 when you export to jpeg, it gives the option of saving a file from 1 (worst quality) to 10 (best quality ~ least compression).
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04/29/2002 10:26:13 PM · #3 |
The file sizes straight from the camera were the 30K-132K
The other, the one that went from 80K to 246K was after enhancing and saving. I'll have to check on that compression number.
Also the camera saves as a JPEG file, if that makes a difference
* This message has been edited by the author on 4/29/2002 10:27:06 PM. |
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05/07/2002 04:29:11 PM · #4 |
It all has to do with the way the camera CCD (sensor) detects light. Sometimes a slight difference in color, or angle, or something else that seems slight to us can result in a lot less or a lot more data to the CCD.
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05/07/2002 04:52:34 PM · #5 |
As an illustration of this, consider a simple compression scheme which replaces a long list of repeated values with something that says what the value is, and the number of times to repeat it.
So I have a list of 1000 pixels that are all white. so I store white,1000. This is followed by 1000 black pixels, so I store black, 1000.
So for this, we've gone from 2000 values, to just storing
white,1000
black,1000
which is a whole lot smaller.
Now consider instead of a white line followed by a black line, we have a stripped pattern of white, black, white, black, white, black and so on, for 2000 pixels.
In this case we'd store
white,1
black,1
white,1
black,1
white,1
black,1
white,1
black,1
and so on, 2000 times.
So here, a different image is massively larger once it has been compressed. The same sorts of things happen in the camera to compress the images, so small changes can cause much much larger files, typically if more detail is apparent (e.g., a really overexposed picture is usually much smaller as there are lots of white areas)
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05/07/2002 05:04:47 PM · #6 |
Originally posted by GordonMcGregor:
So here, a different image is massively larger once it has been compressed. The same sorts of things happen in the camera to compress the images, so small changes can cause much much larger files, typically if more detail is apparent (e.g., a really overexposed picture is usually much smaller as there are lots of white areas)
Gordon and Count, thanks for that information. It explains a lot!
As for the compression and final "saving" of the photo, I figured out where I can change those values on my software.
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05/07/2002 05:06:36 PM · #7 |
It is primarily the amount of detail which determines the efficiency of the compression, whatever quality setting you use. A sunlit photo of a pine tree with the needles discernable will take 2-10 times the data space (as a JPEG) as the same tree shot silhouetted against a late, dim sunset.
For a practical experiment, set up a brightly patterened cloth with a few things on it. Shoot it once with the flash, and once from the same spot with only a table lamp across the room for illumination.
TIFF files will take about the same amount of disk space regardless of the photo's content, unless you implement the LZW option in Photoshop (I don't, myself). TIFF files are otherwise (pretty) strictly dependent on pixel quantity and color depth.
Remember, storage is cheap! Save your original to CD or ZIP, a copy in "Photoshop" (or equivalent) format on the hard drive. I also save my final (flattened) version in uncompresed TIFF (useful for quickly re-sizing or cropping for other uses, such as DPChallenge!), and in both Hi-Res (300 ppi) and Lo-Res (72 ppi) JPEGs.
My PC came with Adaptec DirectCD -- you can format a CDR/RW to accept "packet writing" where you drag files onto the CD as if it were a floppy, instead of having to write the whole CD at once. I use that to immediately backup (mirror) the photo folder on my hard drive. Then, I periodically go back and burn a normal, multi-platform CD-R from the hard disk as a true archive.
I've been sizing/matting my photos to match standard photo print sizes and getting prints made through Ofoto.com -- I've been happy with both the quality (Kodak extra-heavy paper) and service so far. If you want prints on Fuji paper instead try Shutterfly.com. These are laser-exposed to true photo paper -- no dots, no inks, known archival characteristics. A 4x6 @ 300 ppi JPEG typically runs about 1.4-2.2mb. The TIFF from which it derives runs about 6.2mb.
If you haven't tried one of these services, send me a note (name & working email) and I'll send you a link which will get us each some free prints.
N.B. I DO NOT work for either of these companies!
N.B. Side benefit: free, off-site backup of your files!
* This message has been edited by the author on 5/7/2002 5:15:47 PM. |
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