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06-20-2012, 02:10 PM   #1
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my raw question

the 645d converts raw photos to dng or pef in-camera.i have several editors that will open dng files but,none that open pef except the one that came with the camera.i also have a seperate converter that works with dng files. my questions.

#1 is the dng file uncompressed and contain all the data as it comes from the camera?
#2 if i use my dng converter to change it to jpeg or tiff ,are they compressed and do they lose data?
#3 if i open a dng file just look at it and then save it to tiff or jpeg, is it compressed and does it lose data.?
i hav asked this question before but received confusing answers.

06-20-2012, 02:13 PM   #2
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1) DNG is a universal RAW type as created by Adobe. It is effectively the same as PEF.

2) You cannot edit a DNG/PEF/RAW file, afaik. You can only make edits and save as a picture file (JPEF, TIFF, PNG, etc).TIFF files are uncompressed images. JPEGs are compressed and lossy.

3) See #2.
06-20-2012, 02:31 PM   #3
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You can also save Your edited RAWs in full 16bit per color as TIFF.
This will need lot more HD space.

-Linus-
06-20-2012, 03:33 PM   #4
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QuoteOriginally posted by -Linus- Quote
You can also save Your edited RAWs in full 16bit per color as TIFF.
This will need lot more HD space.

-Linus-
when i save them in tiff ,do lose any IQ?

06-20-2012, 03:53 PM   #5
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If you save you tiff files as 16-bit, you do not lose any data--whether that is important in terms of IQ requires a long post. You will lose information if you save your tiffs as 8-bit.
06-20-2012, 04:07 PM   #6
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So bit depth indicates the number of luminance levels in each channel. In order for you to create the illusion that a gradient goes from black to white without any steps, you need approximately 200 levels of gray. 8-bit is the magic number because it has 256 levels. However, if you make changes to the data in curves or levels, you can lose information with an 8-bit image which will cause banding--you probably have seen banding in skies when there are not enough luminance levels to describe the gradient.

The 645D make 14-bit RAW files, which has 16384 levels in each color channel. That means you can push things around with less of a chance of banding. When you save that as a 16-bit tiff, the number of real levels are preserved--there are 65536 levels in a 16-bit image per color channel, but most levels have no pixels with those luminance values, although things can get moved around as you process. When saved as 8-bit, the numbers have to be binned into the available 256 levels.

Now, if you have a perfect image, an 8-bit file will look just as good as a 16-bit file. They will have the same IQ. Our eyes really cannot distinguish between the 16 million colors in an 8-bit file from the 275 trillion possible colors in a 16-bit file--they look the same.

I will leave the choice of color space for another day. But I recommend open your RAW as Abobe RGB, which is a printer color space. sRGB is a monitor/web space and is easy to convert to. I don't recommend Pro Photo RGB.
06-20-2012, 04:51 PM   #7
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1. The DNG is uncompressed. It contains ALL the data off the sensor.
2. JPG = compressed = Loss of data. TIFF = compressed or uncompressed, depends on your settings for saving the TIFF. If compressed TIFF is selected it is usually a lossless compression that is used, meaning no data is lost.
3. The JPG or TIFF file you save will be as per answer 2. The DNG file will be unaltered, so no loss of data.

Regards

Chris

QuoteOriginally posted by bull drinkwater Quote
the 645d converts raw photos to dng or pef in-camera.i have several editors that will open dng files but,none that open pef except the one that came with the camera.i also have a seperate converter that works with dng files. my questions.

#1 is the dng file uncompressed and contain all the data as it comes from the camera?
#2 if i use my dng converter to change it to jpeg or tiff ,are they compressed and do they lose data?
#3 if i open a dng file just look at it and then save it to tiff or jpeg, is it compressed and does it lose data.?
i hav asked this question before but received confusing answers.
06-20-2012, 05:23 PM   #8
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1) DNG files are exact copies of what the sensor produced and are typically compressed with a lossless compression (think of zip files)
2) Yes to jpeg, it depends on the color depth of the TIFF (8 vs 16 bit) and the original dynamic range of the DNG. TIFFs can also be compressed with a lossless compression.
3) You cannot view a DNG file in the traditional image view mode. What you see on the display is a converted image from DNG to a 24-bit (usually) bitmap. When you save the image you are saving a copy of the bitmap (the converted DNG) with the options in #2.

One thing to remember is to always archive a copy of your DNG file for all important images. While converting it to 16-bit TIFF will preserve all the information from the DNG, you are actually saving the converted data.

DNG being a RAW format has a matrix of single colored pixels with 10-, 12-, or 14-bits in whatever pattern the camera's sensor outputs them. TIFF files have RGB (Red-Green-Blue) values of 8 or 16 bits for each pixel (24 total bits for 8-bit TIFFs and 48 total bits for 16-bit TIFFs). The way these 24 or 48 bits were derived from the original DNG data is related to the RAW converter software used. The conversion process is improving constantly and newer versions of RAW converters perform better in terms of extracting cleaner and sharper images with more dynamic range.

Unless you know the exact algorithm used to convert RAW to TIFF, it is next to impossible to regenerate the original DNG. You will be very pleasantly surprised to revisit old images (e.g. 2-5 years old) and reprocess them with the latest software.

In an analogy to film photography, the DNG file is the exposed film, and the converter is the chemicals and the process (formulas, times, etc.).

06-20-2012, 05:57 PM   #9
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QuoteOriginally posted by demp10 Quote
1) DNG files are exact copies of what the sensor produced and are typically compressed with a lossless compression (think of zip files)
2) Yes to jpeg, it depends on the color depth of the TIFF (8 vs 16 bit) and the original dynamic range of the DNG. TIFFs can also be compressed with a lossless compression.
3) You cannot view a DNG file in the traditional image view mode. What you see on the display is a converted image from DNG to a 24-bit (usually) bitmap. When you save the image you are saving a copy of the bitmap (the converted DNG) with the options in #2.

One thing to remember is to always archive a copy of your DNG file for all important images. While converting it to 16-bit TIFF will preserve all the information from the DNG, you are actually saving the converted data.

DNG being a RAW format has a matrix of single colored pixels with 10-, 12-, or 14-bits in whatever pattern the camera's sensor outputs them. TIFF files have RGB (Red-Green-Blue) values of 8 or 16 bits for each pixel (24 total bits for 8-bit TIFFs and 48 total bits for 16-bit TIFFs). The way these 24 or 48 bits were derived from the original DNG data is related to the RAW converter software used. The conversion process is improving constantly and newer versions of RAW converters perform better in terms of extracting cleaner and sharper images with more dynamic range.

Unless you know the exact algorithm used to convert RAW to TIFF, it is next to impossible to regenerate the original DNG. You will be very pleasantly surprised to revisit old images (e.g. 2-5 years old) and reprocess them with the latest software.

In an analogy to film photography, the DNG file is the exposed film, and the converter is the chemicals and the process (formulas, times, etc.).
from the beginning i made a practice of keeping the originals on a external drive and copying them to working folders and renameing the prints.
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