Question about sensorsize versus picturesize.

[Erikvw]

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Can someone explain to me, that when i shoot with my CL a RAW/DNG picture, the size of the picture is about 42MB in Lightroom CC, although my sensor is a 24 megapixel size. 

I thought my picture would be 24 MB? Where do i make a misstaken in thinking?

kind regards Erik.

[M.piras]

Sorry, why it should be 24Mb? Equation is not 1Mp=1Mb also because each pixel have more than one byte instruction for DNG usually has color instruction and luminance instructions by this you can already understand why a 24Mp sensor is around double in weight.

M.

Edited January 19, 2019 by M.piras

[ramarren]

I'm not sure where the notion that the 24MPixel raw image data from your CL would amount to 24Mbytes of data comes from.

The size of the raw file is about 42Mbyte (actual size of a recent sample CL photo, DNG only, is about about 45.6 Mbytes on my disk). The raw file contains EXIF metadata, a JPEG preview or thumbnail, and the sensor data which is a mosaic'ed array, approximately 6014x4014 elements in size, of RGB values expressed as discrete integer values up to 15 bits in size. Considering the integer values to be represented by 14 bit numbers, the sensor data alone calculates out to about 40.2 Mbytes, uncompressed, leaving about 2-4 Mbytes for the JPEG thumbnail and EXIF metadata. 

Convert that raw file to RGB data and output to full resolution as an uncompressed, 16-bit per component TIFF file nets a 6000x4000 pixel image contained in a 151 Mbyte file.  Convert the raw file to RGB data and output as a minimum compression/maximum quality JPEG with 8-bits-per-component nets a 6000x4000 pixel image contained in a 16.8 Mbyte JPEG file. 

The size of the original DNG file is somewhat variable due to the variable size of the compressible JPEG thumbnail it contains. The size of the outputted uncompressed, full resolution TIFF file is pretty much fixed. The size of an outputted full resolution JPEG file can vary based upon how much compression you apply and the subject matter. 

[pico]

Wow, some complex but accurate explanations are not particularly helpful. Best to consider that to handle a .dng the computers software and operating system need more room to work. It is good that the camera does not need all the 'room' post-processing does.

 

[jaapv]

Boy, am I happy that I still have a huge Cheese-grater MacPro. These small new contraptions could never fit the full frame files in. 

[01af]

One pixel is 14 bits. So 24 mio pixels is 336 mio bits or 42 mio bytes.

Edited January 19, 2019 by 01af

[scott kirkpatrick]

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Actually, one pixel in a DNG file on the CL or SL gets 14 bits, just less than 2 bytes.  And they pack them in tightly.  The variation in final file size is due to three jpegs included for thumbnails and for review on the LCD and EVF.

[pico]

14 minutes ago, scott kirkpatrick said:

Actually, one pixel in a DNG file on the CL or SL gets 14 bits, just less than 2 bytes.  And they pack them in tightly.  The variation in final file size is due to three jpegs included for thumbnails and for review on the LCD and EVF.

The receiving OS might rationalize storage to round the 14 bits to a rational power of two - 16 bits.

Edited January 19, 2019 by pico

[scott kirkpatrick]

A DNG file on disk occupies the same space that it takes on the CD card, but I assume that any program reads it into memory as a series of 2 byte integers before trying to do anything with the information.  It's all in the Adobe DNG spec as a not very common option.

[pico]

7 minutes ago, scott kirkpatrick said:

A DNG file on disk occupies the same space that it takes on the CD card,

I will look into that assertion, but I am pessimistic. Back later.

[ramarren]

Since I was just uploading files from my CL onto my Mac, I checked. Exactly the same file sizes on my card as on my computer. How an application handles the data once it reads it in is up to the DNG spec, the metadata descriptors in the file, and the app's algorithms, and is irrelevant to the file size on disk. 

I could easily surmise that the words are written to storage as a continuous bit stream, since the offset, size, and number of data elements per row are well known by the descriptors in the metadata. It's how we used to write and read image data when I was working on digital image processing software for NASA an aeon ago ... except we didn't have metadata in the image files, we just know how many bits to read from the file and how they were organized. 

[jaapv]

3 hours ago, scott kirkpatrick said:

Actually, one pixel in a DNG file on the CL or SL gets 14 bits, just less than 2 bytes.  And they pack them in tightly.  The variation in final file size is due to three jpegs included for thumbnails and for review on the LCD and EVF.

Assuming it is a straight write, not using a LUT like the M8.

[adan]

Erik, the others keep circling around this and making it more complex than it has to be.

The key point is that your camera's 24 megapixels produce 2 bytes of data each, or 48 megabytes. That gets compressed (like a .zip file, more or less) to the final .DNG file size, which is thus smaller than 48 million, but quite a bit larger than 24 million, bytes.

Which is a good thing, since it gives you quite a bit of leeway to play with the data in your computer, making the picture darker or lighter, or this or that color, without visible "damage" to the picture. You have extra data above what a computer screen or print can generally reproduce anyway.