25mb jpegs

Jacqui O

Jacqui O

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Jacqui
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This has just intrigued me -
I was uploading a photo on to a site the jpeg was 4.5mb, I use a D700.......... It requested - for professional jpegs at least 25mb I can't get my head round how they are that size. :gag: :nuts: Would some one explain in layman terms ... Please
 
JPGS are compressed, when opened, they decompress. So although the file looks small, its not when uncompressed.
Alamy stock site state they want uncomprressed Jpgs of a certain size. The files I upload from my D700 are usually no more than 10Mb, but each is well past thier desired base level once open and decompressed.
 
25Mb seems a bit "elitist" , the Nikon flagship D4 only has a 16Mb sensor, are you expected to "stitch" picces together or up-sample in photoshop.
 
vizzair said:
25Mb seems a bit "elitist" , the Nikon flagship D4 only has a 16Mb sensor, are you expected to "stitch" picces together or up-sample in photoshop.
Click to expand...
You're confusing bytes and pixels.

The D4 has a 16 MP sensor. How much data you need to store the image depends on the bit depth you're working to. The sensor records 14 bits, so an uncompressed RAW file would require about 5½ bytes per pixel, and the file size would be about 84 MB. (OK, Nikon RAW images are non-destructively compressed, but this is just for illustration.) A 16-bit TIFF would require 6 bytes per pixel, hence 96 MB. An 8-bit uncompressed JPEG would require 3 bytes per pixel, hence 48MB.
 
vizzair said:
25Mb seems a bit "elitist" , the Nikon flagship D4 only has a 16Mb sensor, are you expected to "stitch" picces together or up-sample in photoshop.
Click to expand...

My D700 "only" has a 12Mp sensor, yet easilly meets the standard required for alamy. Uncompressed JPGs are around 30MB I recall. The size of the sensor in Mp isnt the same as a 25MB picture.
 
whoops - forgetting that 1 pixel is a minimum of 3 bytes.
 
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