Is this image (exported as "Original") being compressed?

New Here ,
Feb 03, 2021 Feb 03, 2021

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Hello,

 

I have taken a couple of images and am wanting to get a better understanding of the DNG file type compared to TIF.

 

I have taken an image using the DNG capture setting and then exported it. For the first image, I exported it as "Original". For the second image, I exported it as a 16 bit, uncompressed, largest available dimensions "TIF".

 

In the EXIF data:

The Original DNG export shows 96 dpi, 24 bit depth, 3024x4032, 14.1 MB

The TIF export shows 300 dpi, 48 bit depth, 3024x4032, 69.8 MB

 

What I would like to know is if the "Original" DNG export is actually exporting the "raw-ish" image that my camera has taken or if things are being compressed somehow in the process? In another thread (https://community.adobe.com/t5/lightroom-classic/checking-compression-of-dng-file-format/m-p/1104550...), we compared something similar and saw that the "Original" image export may be undergoing "lossless" compression. Is this lossless compression severe compared to the TIF?

 

The TIF has a greater dpi and bit depth, so is this a higher quality image? I would have thought that an original DNG capture would be just as high of quality?

 

Here are the sample images that I am comparing:

1.png

 

and zoomed in:

2.png

If anyone can help to explain the image quality and file format specifics, I'd really appreciate it!

 

Thank you!

 

 

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Adobe Community Professional ,
Feb 03, 2021 Feb 03, 2021

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First of all, DPI or really PPI (pixels per inch) is basically meaningless. The image dimensions is all that matters. Changing the PPI doesn't change the quality of the image in any sense. Next, what are you using to look at the two different images? If you are not looking at the DNG file with a raw converter then all that is being displayed is the embedded JPEG preview, and that is one explanation for the reduced PPI. Normal image viewers cannot display raw image data, and have to resort to displaying and reporting the characteristics of the embedded JPEG preview. The file size comparison seems about right, in my opinion when considering what I have explained.

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New Here ,
Feb 03, 2021 Feb 03, 2021

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Hi Jim,

 

Thank you for your response! I am looking at the images in ImageJ (an open source software). DNG import is supported when using a plugin called Bio-Formats.

However, you mentioned that it seems as though the JPEG preview is being read instead of the raw image?

 

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New Here ,
Feb 03, 2021 Feb 03, 2021

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This is the Metadata after import to ImageJ if that helps for comparison. 

 

3.png

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Adobe Community Professional ,
Feb 03, 2021 Feb 03, 2021

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The fact that it is indicating for the DNG file that it is 8 bit, and JPEG compression is clearly an indication that it is displaying the JPEG preview that is embedded in the DNG file. That viewer is NOT a raw converter and is not capable of reading the raw image data and displaying the raw data or reporting the true values of the raw image.

 

If you want a true comparison of the images you'll need to open them in a raw converter and get the information from there. Lightroom Classic or Camera Raw would give you a good picture of the true value, but I don't think you'll get much information from Lightroom cloudy.

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Adobe Community Professional ,
Feb 03, 2021 Feb 03, 2021

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I don't know anything about that software. But that would be my suspicion. Unless the software is actually a raw conversion software, it could "support" the DNG format but only to the extent that it is capable of rendering the embedded JPEG preview. Does that software support native raw formats?

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New Here ,
Feb 03, 2021 Feb 03, 2021

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I am seeing that it support many of the raw formats, but I do not specifically see .dng listed.
Here is their list: https://docs.openmicroscopy.org/bio-formats/5.8.2/supported-formats.html

 

If it is reading the JPEG preview, would it not have obvious artifacts in the images? I can tell a difference between the "DNG" and TIFF images, but the difference does not seem very extreme even when fully zoomed. I know that I am missing data between 8 bit color channels in DNG and 16 bit channels in TIFF, but is the 256 vs 65,536 levels of color the only difference?

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Adobe Community Professional ,
Feb 03, 2021 Feb 03, 2021

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I'm only telling you what I believe is happening. If the DNG file contains 8-bit data then you must be using Photoshop Elements instead of Lightroom because DNG files in Lightroom are 16 bit images, and the JPEG preview is an 8-bit image. I have only told you what I understand. Apparently you don't want to accept my explanation, so I will step aside and let you wait for someone else who might have a better explanation.

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New Here ,
Feb 03, 2021 Feb 03, 2021

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Hi Jim,

 

Sorry, I fully accept and appreciate your explanation. I'm just trying to understand the overall concepts of the different file formats and how they are presented visually and in the metadata. It doesn't seem that DNG is used too often with ImageJ analysis, so that is adding some complication.

 

Thank you for your help!

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Adobe Community Professional ,
Feb 03, 2021 Feb 03, 2021

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If you want to truly analyze an image then you want to use software that is fully capable of doing the analysis. An image viewer isn't going to be capable of providing a full analysis of the raw image, and that includes DNG files. You need to use a true raw converter and its tools to extract the information. An image viewer might indicate that it "supports" different raw formats, but in reality it isn't reading the raw image data. It is only reading and interpreting the information that is in the embedded JPEG preview file. And the JPEG preview file isn't going to report the traits of the raw data because it really is a separate file, even though it is embedded within the raw file or the DNG file. So if you want to compare apples to apples then you need to use the right software to do it. It really is that simple and straight forward.

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