Hi, i have been shooting for about 6 months with my d7000. I just noticed that my image are now coming out in size to about 5.5 mgs. I have large jpg Fine selected but it used to say, when I looked at image size on my computer, it was 16.1 mg and now it doesn't. Any idea what might have caused this change? I am opening these photos with a generic microsoft product.
Basics: Image size is dimensioned in
pixels. File size is dimensioned in
bytes. These are different properties. It was not clear which you were discussing?
D7000
Large JPG image size is 4928x3264 pixels, or 16 megapixels.
RGB images are 3 bytes per pixel (assuming normal 24 bit color). So 16 megapixels x 3 is 48 million bytes, every time. This is simply the size it is, anytime it is opened into computer memory. But you can choose Large, Medium, or Small size, which are different dimensions in pixels. Digital images are dimensioned in pixels.
But
JPG files are seriously compressed. The files themselves are much smaller than 3 bytes per pixel. This file size depends on JPG compression choice (Fine, Normal, Basic). Still same image dimensions in pixels, but a smaller JPG file is less image quality than the biggest JPG file. This file size only applies while in the JPG file. They are still the same 16 megapixels when opened into computer memory.
(NOTE Normal JPG is NOT normal, it is somewhat poor quality. Fine is normal for JPG).
Photo editors sometimes show both image and file sizes (Adobe). Others may show one or the other?
The Nikon manuals (chart under Memory Card Capacity, page 320 in D7000 user manual) shows expected file sizes, and says 7.8 MB for Large Fine JPG, and 4.4 MB for Medium Fine, or 3.9 MB for Large Normal, etc.
However, these JPG files sizes are "average" approximations, and JPG file size will vary a little depending on the image scene content. An image full of fine detail will be larger, and an image full of smooth blank areas (wall, sky, etc) will be smaller. A hundred varied JPG images (all same pixel dimensions) might vary in file size over a 2 to 1 range. The smaller ones will contain blank space, and the larger ones contain much busy detail.
See
Pixels, Printers, Video - What's With That? for a summary of these digital basics.
