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08-21-2013, 09:50 PM   #1
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Photo size

How it comes that in most of times when I am starting processing a DNG file ( Pentax K01 raw ) of 14MB size it ends with a jpg file of less than one MB ?

Any explanation !!?

By the way : I use Lr 3.6 and this is not the case with similar size Nikon NEF file processing !


Mustafa

08-21-2013, 11:41 PM   #2
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QuoteOriginally posted by mns Quote
How it comes that in most of times when I am starting processing a DNG file ( Pentax K01 raw ) of 14MB size it ends with a jpg file of less than one MB ?

Any explanation !!?

By the way : I use Lr 3.6 and this is not the case with similar size Nikon NEF file processing !


Mustafa
JPEGs are compressed in a lossy manner, meaning that they sacrifice some detail (usually it's indiscernible) in order to get the filesize down. They are also 8-bit files, so the color values for each pixel aren't as precise as what you'd find in 12-bit raw files. Also, DNG files are only losslessly compressed, as they store all the information that was originally recorded at the time of capture.

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08-21-2013, 11:54 PM   #3
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All is down to the compression applied. In Lightroom while you are exporting your photos, there is an option for that, with slider to apply the desired compression lever. By default it is probably 80% which is quite severe - but if you set it all the way up to 100% then your JPG files will be of much higher quality but large - even 6-8 MB. The good compromise for me usually is about 90-95% of compression , which I recommend for web use.

EDIT:
Also if you scale your images down that also reduces the size - for example for web upload (like for forum ) I usually use the option to scale the Long Side of image between 850 - 1024.
08-22-2013, 05:12 AM   #4
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QuoteOriginally posted by Adam Quote
JPEGs are compressed in a lossy manner, meaning that they sacrifice some detail (usually it's indiscernible) in order to get the filesize down. They are also 8-bit files, so the color values for each pixel aren't as precise as what you'd find in 12-bit raw files. Also, DNG files are only losslessly compressed, as they store all the information that was originally recorded at the time of capture.
I understand you but I donít understand the difference in size of the jpg outcome file between my Nikon d7000 and my Pentax K01( same sensor ) ...I used to process my nef file and get jpg of 2-3MB however with Pentax the outcome jpg of dng processing is about 850KB ?


08-22-2013, 07:12 AM - 1 Like   #5
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By default Jpeg's are stored at 72ppi which is all the resolution you can see on screen, Raw files are usually stored at around 200 - 300 ppi because they might be used for print. the ppi doesn't make any difference to the file data only how it's viewed on your computer unless you save it at these settings. You can't alter a Raw file as they are read only files, any alterations are stored in a 'sidecar' .xmp file and you can only save in one of the pixel based file types, Jpeg, PNG, Tiff etc. you cannot save as a Raw file. But when you are saving a version of a Jpeg it's important that you use Save As and alter the file name.

If you open a Raw file it will be around 46Mb and would print natively at 16.427" X 10.88". If you convert to 72ppi without altering anything else it will still be a 46Mb file, and it would now print at 68.444" X 45.333", but that's not what you normally do, you usually constrain the image size so the file size alters downwards to 2.65Mb and dumps 43.35Mb of data in the process, that's using the least amount of compression, the 2.65Mb will be even lower depending on how much compression is applied. The same happens when you save as Jpeg in camera, setting one, two or three stars in the camera determines how much compression is applied, a one star file might well be less than 1Mb.

Note Dpi and ppi are not the same thing, dpi is the resolution of a printer or scanner, ppi is what the computer alters when you view the image on screen, the more you zoom into an image the lower the ppi gets and the larger the image gets, you can zoom into the point that you can see the individual pixels. Ppi works by altering the size of the pixels the larger the pixels the larger the image size.

EDIT: May be I should explain why a 20Mb Raw file increases to a 46Mb file when opened in Photoshop. Mainly it's because you are also creating a new .xmp 'sidecar' file or opening the old one associated with this file which is the same size and resolution of the original Raw file, this doubles the file size to 40Mb. On top of that PS creates data within the .xmp file and imports some of the EXIF data, lens type for instance so it can apply lens correction, the data is how many pixels across and down and a memory map of them, this is required by the Tiff format and the PSD format which is a Tiff derivative.

Chris

Last edited by ChrisJ; 08-22-2013 at 07:36 AM. Reason: Addition
08-22-2013, 10:31 PM   #6
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Nice explanation Chris. Clear and concise.
08-23-2013, 03:53 AM   #7
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Thank you very much for your comments and explanation
08-23-2013, 05:52 AM   #8
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QuoteOriginally posted by mns Quote
How it comes that in most of times when I am starting processing a DNG file ( Pentax K01 raw ) of 14MB size it ends with a jpg file of less than one MB ?

Any explanation !!?

By the way : I use Lr 3.6 and this is not the case with similar size Nikon NEF file processing !


Mustafa
What size and settings in LR for these jpg's?

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