Why do 20d file sizes differ & compression amounts?

[DavoMrMac]

Hello All

Finally got out for the day and really enjoyed my 20d, experimenting with DOF and other things, a great day, and great shots, with about 80% keepers.

My question is about files sizes. I had my 20d set to RAW + JPEG LargeFine all day.

Some of the JPEGS are 1.9Mb, some 2.2Mb, some even 2.5Mb. The RAW files range from 7Mb to 9.7Mb. The only thing that may have been changed is my aperture setting, but in some cases this is the same and the file sizes still differ.

I also noted that in iView Media Pro, there is a listing under the images information called 'Compression' and this differs from like 1:6 to 1:16, with the JPEGS having a higher amount of compression.

Why do the file sizes differ and why does iView tell me that there is a different amount of compression on shots that are shot with the same settings?

Thanks in advance.

[Deckyon]

The colors and tones of the image captured lends towards the difference in file size. This is normal across the board for digital cameras.

I do not use IView Pro, so I cannot respond to the differences in that application.

[jbradc]

It is due to the detail in the subjest being photographed. For example if you take a photo of a blank wall it will contain less data than a landscape with trees and mountains of different color and texture.

[DavoMrMac]

Thanks Brad and jbradc, I understand that now, more colours/detail = bigger file.

I know you said you do not use iView, but do any of the applications you use tell you the compression amount, as I guess this is store in the information recorded by the 20d with the image.

The question about compression could be related to iView, but I think it is related to the 20d, so I am now left wondering why it applies different amounts of compression to images with the same internal settings on the camera?

Also, was I wrong in my assumption that RAW = No compression.

[Vita Rara]

The question about compression could be related to iView, but I think it is related to the 20d, so I am now left wondering why it applies different amounts of compression to images with the same internal settings on the camera?

The quick answer is that the 20D is applying the same amount of "compression" to each JPG file. The issue is that the "compression" isn't the right term. You set the quality level of a JPG when you save it. This tells the JPG algorythm how aggresive it should be in throwing away information.

So, with the same quality level set you can have differing levels of compression depending on the level of detail in the original image.

Also, was I wrong in my assumption that RAW = No compression.

Yes, the RAW file format uses lossless compression. Whereas JPG uses lossy compression.

Later,

Mark

[DavoMrMac]

So the RAW file will still show in the file information that it has say a 1:6 compression, but this is lossless...

and the JPEG will show the info for the amount of compression too, but this is a lossy type of compression...

and in the same way as another answer explained, if the image is say mainly white, the compression may be for example 1:2, but if there is a lot of detail/colour it may be 1:6...

is this correct?

[Vita Rara]

So the RAW file will still show in the file information that it has say a 1:6 compression, but this is lossless...

Correct.

and the JPEG will show the info for the amount of compression too, but this is a lossy type of compression...

and in the same way as another answer explained, if the image is say mainly white, the compression may be for example 1:2, but if there is a lot of detail/colour it may be 1:6...

is this correct?

Somwhat, except that the less detail in the image will result in a higher compression ratio, say 1:10, and the more detail the lower 1:2.

Later,

Mark

[CyberDyneSystems]

The largest variation in file size is seen when adjusting ISO,. higher ISO = larger file size,. this is due to "detail"

Your camera will even do the math ahead of time to the best of it's ability,. and adjust the "shots remaining" number as you adjust your ISO.

[Phil V]

The largest variation in file size is seen when adjusting ISO,. higher ISO = larger file size,. this is due to "detail"

But that 'datail' is known to the rest of us as 'noise':o