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I recently took a long exposure shot of the sky at night on my OnePlus 5. The RAW image when viewed on phone turned out to be great, pitch black sky and white-red-blue stars! Pretty excited, I decided to show the picture to my family on a bigger screen. I quickly transferred the .dng (about 31 MB) to my laptop and opened it using Picasa photo viewer. And bam! The picture was nothing but noise, yellow-greenish dots everywhere and stars barely visible. I uploaded the image on 'Online Raw Converter' but the same output there. Can someone tell me why does this happen? And, is there any way I could view the image onto a PC with output like that on my phone?

Ps. I'm attaching low quality screenshots of the results on Phone and PC respectively. Sorry the screenshot of phone is 16:9 instead of original pic 4:3. Make sure to look in dark, there's about a 1000 distinct stars in this image.

Resolution : 3496x4656

File Size : 31.07 MB

Focal Length : 4.10 mm

Aperture : f/1.7

Exposure time : 10"

ISO : 100

ON PHONE (Gallery, Google Photos, Any app)

enter image description here

ON PC (Picasa photo viewer, Online Raw Converter) enter image description here

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2 Answers 2

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Picasa is automatically applying exposure correction to your very dark image. Since this scene is intentionally very dark, this automatic is going wrong. It brightens the image up considerably, thereby making the noise, which was hidden in the shadows previously, visible.

You can easily change this by editing the picture and turning the exposure correction down (sorry, don't know how it is called in picasa specifically).

Note that the phone apps most probably simply show the embedded JPEG preview image. Some image viewing programs on your PC will do that as well. But you should be able to get an even nicer image with a bit of work in a decent raw processor.

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Any time you view a "raw" image on any device, one of two things is happenning:

  • The raw data in the file is being processed and interpreted by the application you are using to view the image. That application may be a simple photo viewer built into the device's firmware, or it may be a sophisticated photo editor such as Lightroom or Photoshop. There is no single "correct" interpretation of the data in a raw image file. Each application can interpret the raw data in the file differently. There is no "one" way to render the linear 12-14 bit monochromatic luminance values contained in a raw file in color on a 8-bit three color device. The raw data must be processed to be viewed.
  • You are seeing a preview jpeg generated by the camera that took the shot. This preview image is appended to the file containing the raw image data, along with the metadata generated by the camera. Many devices will use this preview image when you open a "raw" photo.

Some applications display the preview image until they can render an image created by interpreting the raw data itself. Many applications have user selectable options that allow the user to select what is displayed when a raw image file is opened: the jpeg preview or one of many possible interpretations of the raw data using an automated routine or one of many selectable default processing profiles.

Related questions:
RAW files store 3 colors per pixel, or only one?
Why is there a loss of quality from camera to computer screen
Why do RAW images look worse than JPEGs in editing programs?
While shooting in RAW, do you have to post-process it to make the picture look good?
Why do my photos look different in Photoshop/Lightroom vs Canon EOS utility/in camera?

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