I hope this wasn't asked a million times and I missed it. I'm just curious as the why my files are twice the size with the d7000 compared to d90? Both shot raw. Looking at some of my d90 they were about 10 to 11 mb while the d7000 is about 20mb. It doesn't have twice the mp, so I'm guessing there is more to the file size than the mp?

Thanks you

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You may be confusing mega pixels with mega bytes. The D90 has 12.3 effective megapixels and 12.9 total megapixels. The D7000 has 16.2 effective megapixels and 16.9 total megapixels.

Another issue is related to compression. There may be different compression algorithms used for the two cameras. Even with the same algorithm, images vary in the amount of compression possible depending on the level of detail in the image. And once you open an image and edit it, the embedded small JPEG is replaced with a larger JPEG.

My experience is the compressed vary. I looked at a series of similar unedited test images. My "out of the camera" NEF files from the D7000 resized as small JPEGs are posted here. Both images have the same number of pixels and the same image data. The only difference is compression based on the image data in the file.

The first file was 16.2 mb. After opening this file in Capture NX2 and making a single edit (noise reduction - and only the original image is attached), the resulting file size was 18.7 mb. And the image size has not changed - it is always 16.3 megapixels.



The second image was 13.1 mb. There is more variation in the background, but more compression was achieved.



I'm not going to claim to be able to explain how the compression algorithm works. But I can comment on the result.

And by the way - I was testing whether AF would work using a 2.0 teleconverter on a 300mm f/4 lens. These are the extreme file sizes. Most of the files were around 14-15 mb. And for the record, AF does work with the center sensor even in relatively low light.

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Well there are a number of things that affect file size such as image content, compression and bit depth. The D7000 has both 12-bit and 14-bit raw file ability and I believe the default is 14-bit. The D90 only has 12-bit.

Also the D90 I believe only uses visually lossless compression where as the D7000 uses by default lossless compression with the option to switch to visually lossless.

So summing up, The D7000 has 4 more MP, higher bit depth and a different compression scheme by default.

Hope this helps.

Pete

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