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Is there a way to change the aspect ratio of a DNG file?

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5

I am shooting raw DNGs through an anamorphic lens that squeezes my image by a factor of 1.33 in the horizontal direction. I can easily correct the aspect ratio by opening the image in Photoshop and stretching it horizontally by 133%, but then I have to bake-in all of my choices about colour and exposure adjustments.

Is there a way to change the aspect ratio of a raw photo (by stretching rather than cropping it) while leaving it in its original DNG format?

photo-editing dng aspect-ratio

share|improve this question

edited Jul 3 at 18:05

mattdm

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add a comment | 

5

I am shooting raw DNGs through an anamorphic lens that squeezes my image by a factor of 1.33 in the horizontal direction. I can easily correct the aspect ratio by opening the image in Photoshop and stretching it horizontally by 133%, but then I have to bake-in all of my choices about colour and exposure adjustments.

Is there a way to change the aspect ratio of a raw photo (by stretching rather than cropping it) while leaving it in its original DNG format?

photo-editing dng aspect-ratio

share|improve this question

edited Jul 3 at 18:05

mattdm

125k4040 gold badges368368 silver badges668668 bronze badges

asked Jul 3 at 16:39

UbiquitousUbiquitous

13544 bronze badges

add a comment | 

I am shooting raw DNGs through an anamorphic lens that squeezes my image by a factor of 1.33 in the horizontal direction. I can easily correct the aspect ratio by opening the image in Photoshop and stretching it horizontally by 133%, but then I have to bake-in all of my choices about colour and exposure adjustments.

Is there a way to change the aspect ratio of a raw photo (by stretching rather than cropping it) while leaving it in its original DNG format?

photo-editing dng aspect-ratio

share|improve this question

edited Jul 3 at 18:05

mattdm

125k4040 gold badges368368 silver badges668668 bronze badges

asked Jul 3 at 16:39

UbiquitousUbiquitous

13544 bronze badges

share|improve this question

edited Jul 3 at 18:05

mattdm

125k4040 gold badges368368 silver badges668668 bronze badges

asked Jul 3 at 16:39

UbiquitousUbiquitous

13544 bronze badges

share|improve this question

edited Jul 3 at 18:05

mattdm

125k4040 gold badges368368 silver badges668668 bronze badges

asked Jul 3 at 16:39

UbiquitousUbiquitous

13544 bronze badges

edited Jul 3 at 18:05

mattdm

125k4040 gold badges368368 silver badges668668 bronze badges

edited Jul 3 at 18:05

mattdm

125k4040 gold badges368368 silver badges668668 bronze badges

asked Jul 3 at 16:39

UbiquitousUbiquitous

13544 bronze badges

asked Jul 3 at 16:39

UbiquitousUbiquitous

13544 bronze badges

1 Answer
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6

The DNG spec contains a tag DefaultScale:

DefaultScale is required for cameras with non-square pixels. It specifies the default scale factors for each direction to convert the image to square pixels. Typically these factors are selected to approximately preserve total pixel count.

The situation with your anamorphic lens is effectively this: the photosite on the sensor may actually be square, but due to the lens's compression effectively actually represents a rectangle. So, in theory, setting this value should tell RAW converters to stretch the result. Specifically, if you set DefaultScaleH
to 4/3, I think this should indicate what you want. (Note that Exif supports a "rational" data type for fractions, rather than floating point.)

However, this will require support in whatever software you are using, and I'd be very surprised if this widely implemented in a generalized way. For example, I just tried this on a sample file with RawTherapee and darktable, and unfortunately both of these seemed to ignore the value. However, I then broke out the venerable (and unfortunately far less powerful) UFRaw and that does work — the file was stretched as expected.

share|improve this answer

edited Jul 3 at 18:27

answered Jul 3 at 18:10

mattdmmattdm

125k4040 gold badges368368 silver badges668668 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If someone can try this with Lightroom I'll edit that into my answer. Thanks!
  
  – mattdm
  Jul 3 at 21:34
  

  
  
  
  

add a comment | 

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6

The DNG spec contains a tag DefaultScale:

DefaultScale is required for cameras with non-square pixels. It specifies the default scale factors for each direction to convert the image to square pixels. Typically these factors are selected to approximately preserve total pixel count.

The situation with your anamorphic lens is effectively this: the photosite on the sensor may actually be square, but due to the lens's compression effectively actually represents a rectangle. So, in theory, setting this value should tell RAW converters to stretch the result. Specifically, if you set DefaultScaleH
to 4/3, I think this should indicate what you want. (Note that Exif supports a "rational" data type for fractions, rather than floating point.)

However, this will require support in whatever software you are using, and I'd be very surprised if this widely implemented in a generalized way. For example, I just tried this on a sample file with RawTherapee and darktable, and unfortunately both of these seemed to ignore the value. However, I then broke out the venerable (and unfortunately far less powerful) UFRaw and that does work — the file was stretched as expected.

share|improve this answer

edited Jul 3 at 18:27

answered Jul 3 at 18:10

mattdmmattdm

125k4040 gold badges368368 silver badges668668 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If someone can try this with Lightroom I'll edit that into my answer. Thanks!
  
  – mattdm
  Jul 3 at 21:34
  

  
  
  
  

add a comment | 

6

The DNG spec contains a tag DefaultScale:

DefaultScale is required for cameras with non-square pixels. It specifies the default scale factors for each direction to convert the image to square pixels. Typically these factors are selected to approximately preserve total pixel count.

The situation with your anamorphic lens is effectively this: the photosite on the sensor may actually be square, but due to the lens's compression effectively actually represents a rectangle. So, in theory, setting this value should tell RAW converters to stretch the result. Specifically, if you set DefaultScaleH
to 4/3, I think this should indicate what you want. (Note that Exif supports a "rational" data type for fractions, rather than floating point.)

However, this will require support in whatever software you are using, and I'd be very surprised if this widely implemented in a generalized way. For example, I just tried this on a sample file with RawTherapee and darktable, and unfortunately both of these seemed to ignore the value. However, I then broke out the venerable (and unfortunately far less powerful) UFRaw and that does work — the file was stretched as expected.

share|improve this answer

edited Jul 3 at 18:27

answered Jul 3 at 18:10

mattdmmattdm

125k4040 gold badges368368 silver badges668668 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  If someone can try this with Lightroom I'll edit that into my answer. Thanks!
  
  – mattdm
  Jul 3 at 21:34
  

  
  
  
  

add a comment | 

The DNG spec contains a tag DefaultScale:

DefaultScale is required for cameras with non-square pixels. It specifies the default scale factors for each direction to convert the image to square pixels. Typically these factors are selected to approximately preserve total pixel count.

The situation with your anamorphic lens is effectively this: the photosite on the sensor may actually be square, but due to the lens's compression effectively actually represents a rectangle. So, in theory, setting this value should tell RAW converters to stretch the result. Specifically, if you set DefaultScaleH
to 4/3, I think this should indicate what you want. (Note that Exif supports a "rational" data type for fractions, rather than floating point.)

However, this will require support in whatever software you are using, and I'd be very surprised if this widely implemented in a generalized way. For example, I just tried this on a sample file with RawTherapee and darktable, and unfortunately both of these seemed to ignore the value. However, I then broke out the venerable (and unfortunately far less powerful) UFRaw and that does work — the file was stretched as expected.

share|improve this answer

edited Jul 3 at 18:27

answered Jul 3 at 18:10

mattdmmattdm

125k4040 gold badges368368 silver badges668668 bronze badges

share|improve this answer

edited Jul 3 at 18:27

answered Jul 3 at 18:10

mattdmmattdm

125k4040 gold badges368368 silver badges668668 bronze badges

answered Jul 3 at 18:10

mattdmmattdm

125k4040 gold badges368368 silver badges668668 bronze badges

answered Jul 3 at 18:10

mattdmmattdm

125k4040 gold badges368368 silver badges668668 bronze badges