Why do file sizes (megabytes) from same camera differ so much?

[66217]

I can't see why all my photos have extremely different sizes. Whenever I export using JPEG format at Quality 12 in Aperture, some files would end up being of 2MB and some would be of 9MB, and some other would be 5MB. All of them come from RAW photos taken with the same camera (Nikon D40x).

I am desperate because a competition I want to enter requieres images of at least 3MB of size in JPEG format.

Any ideas why this happens?

BTW, in RAW format, all of them are very similar. Around 8MB.

 

[compuwar]

I can't see why all my photos have extremely different sizes. Whenever I export using JPEG format at Quality 12 in Aperture, some files would end up being of 2MB and some would be of 9MB, and some other would be 5MB. All of them come from RAW photos taken with the same camera (Nikon D40x).

I am desperate because a competition I want to enter requieres images of at least 3MB of size in JPEG format.

Any ideas why this happens?

BTW, in RAW format, all of them are very similar. Around 8MB.

JPEG is a compression format, so large parts of an image that are the same color will be reduced to small amounts of information. Raw is literally the raw data off the sensor, so it'll be the bit depth for the number of photosites on the sensor, no more and no less.

Compression changes the size something like this:

If the raw data was:

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABBBBBCDEF

It would take up 44 bytes, but you could compress it like this:

A*35B*5CDEF

Now it only takes 11 bytes.

Now, JPEG is actually "lossy" compression, so unlike my lossless example above, you won't ever get exactly what you started with when you decompress a JPEG for display, but that's the gist of it.

 

[shecky]

(i believe the following is correct. if not, please ignore this post)

this has to do with JPG compression and the amount of color information in the photo. by that i mean a picture of a white dog on a snow covered soccer field in february would not have a lot of variance of tone in the image; its a lot of white with some darker areas, shadows, etc.. therefore there is less variance of color information to keep track of therefore smaller file.

a carnival midway in july might be a huge file due to the amount of color information - all the balloons, the booths, the people, etc... the image has a lot more stuff in it color-wise.

 

[66217]

It makes sense. Seeing the images that came out smaller than the rest, most of them are of an ocean sunrise. Mostly blue and orange.

Would there be a possible way to make them larger? For them to be able to enter a competition.

 

[OreoCookie]

It makes sense. Seeing the images that came out smaller than the rest, most of them are of an ocean sunrise. Mostly blue and orange.

Would there be a possible way to make them larger? For them to be able to enter a competition.

Is file size a criterion? Do you see compression artefacts?
Or how about entering them as tif files instead (either lossless compression or no compression at all)?

If you don't see any differences, the file size is good enough.

 

[dllavaneras]

It also has to do with what you're shooting. A clear sunset will result in a smaller file size than a scene with a lot of grassy areas.

As for the larger file size, you can always change formats and submit it as a TIFF file. You can also keep the metadata and resource fork and the file size will be larger. If all else fails, embed a large thumbnail and you're good to go.

 

[66217]

Is file size a criterion? Do you see compression artefacts?
Or how about entering them as tif files instead (either lossless compression or no compression at all)?

If you don't see any differences, the file size is good enough.

The quality is superb. It preserves the quality perfectly. But since the photos are send via internet, they discard files below the file size they specify (at least this is my understanding so far). I'll try and call them to tell them my particular problem, I think they'll be reasonable enough to understand me.

Maybe sending a tiff file could work. Tho that files go all the way around. They are gigantic.

As for the larger file size, you can always change formats and submit it as a TIFF file. You can also keep the metadata and resource fork and the file size will be larger. If all else fails, embed a large thumbnail and you're good to go.

That last options is a good one. I'll try that.

 

[Lone Deranger]

Running a heavy grain filter over your image will most certainly boost the file size. Hence shooting with higher ISO values will fill up a memory card faster than shooting with ISO 50, for the same reason that shooting grass shots are larger than a blue sky. It's harder for a compression algorithm to describe using minimal data.
I would find it strange that file size on it's own would be a determining factor for a photography competition. Perhaps a certain pixel resolution is required instead.

 

[66217]

I would find it strange that file size on it's own would be a determining factor for a photography competition. Perhaps a certain pixel resolution is required instead.

It's not a formal competition per se. Each Wednesday the newspaper shows the best 6-7 photos of the week (they select the photos, which are not even open to the public). So far, after three times of sending photos, I appeared once.

They put this rules to prevent guys sending photos from cellphone cameras, and to make it a little more difficult for people to send their photos I guess. They must receive hundreds of photos, so this way they just make an extra filter.

Anyways, I am using this chance to call them and suggest them to change some things. For example, if people could vote for the best photo, it would be great. Kinda like the National Geographic weeks photo.