DNG height and width not reported correctly

[rondlg]

Hi

I have ImageMagick v6.8.8-Q8 installed and am finding that DNGs created from camera RAW are mis-reporting their pixel dimensions.

For example a DNG that in lightroom etc shows as 5184 x 3456 is reported by imagemagick as being 5202 x 3465.

Has anyone else seen this and if so is there a solution?


Many thanks


Sharon

[snibgo]

I suspect IM isn't misreporting. Most cameras have sensors with more pixels than advertised. The "advertised" numbers don't seem to be in metadata, so I suspect Lightroom etc uses look-up tables. If the extra trouble you, just crop them off.

[rondlg]

Hi,

many thanks for the quick reply. We tried with four different camera RAW formats (Canon 6D, Canon 60D, Nikon D90, Mamiya 56Mp) and looked at their metadata with Lightroom, Windows file manager and Mac's file browser and in all cases the values are the same and ImageMagick over-reports by 1% in both dimensions.

ImageMagick -> Embedded
5496x3670 -> 5472x3648
4310x3648 -> 4288x2848
6000x9334 -> 5992x9326
5202x3465 -> 5184x3452

On the plus side it's consistent (could there be some rounding on the IM side?) on the negative side we have 100s of thousands of images and I would be nervous cropping off "extra pixels" without knowing what caused the over-reporting.

Still thinking.


Sharon

[fmw42]

I think this topic should be moved to the User's forum, since it appears to related to IM. If I don't get any objections in the next day or so, I will move it.

[rondlg]

Hi,

oh gosh this is my first post - many apologies I didn't realise it was in the wrong place. Please go ahead.

Regards


Sharon

[snibgo]

I suppose the "6000x9334 -> 5992x9326" is the Mamiya Leaf Aptus-II 56 Digital Back? According to http://www.bhphotovideo.com/c/product/8 ... gital.html , this has 9334 x 6000 pixels.

Or perhaps it's the Aptus 10/10R, which http://www.mamiyaleaf.com/leaf_aptus.html says also has 9,334 x 6,000 pixels.

[rondlg]

Hi,

it's the first of those the "Mamiya Leaf Aptus-II 56 Digital Back".

Regards


Sharon

[fmw42]

Hi,

oh gosh this is my first post - many apologies I didn't realise it was in the wrong place. Please go ahead.

Regards


Sharon

Not to worry. This happens from time to time. Also some posts could be in multiple forums. But we prefer that it not be cross posted.

I have now moved it here to the User's forum.

[snibgo]

So, IM is reporting the same pixels as the manufacturer. I suggest you compare the edges as made by Lightroom and IM. You will probably find that a centre crop from IM gives the same pixels as Lightroom. If all the pixels are good, you can keep them, of course.

The Nikon D800 has a similar issue. With some lenses at some apertures a shadow is cast at the edge of the sensor. Cropping the image down to the advertised pixels always gets rid of the shadow.

(No, on second thoughts, this proves your Mamiya is rubbish. Please send it to me, and I will test it thoroughly for you, free of charge, and return it in a few years.)

[rondlg]

Am off to try the centre crop and see what comes out. Will let you know.

In the meantime I'll let our Botany department know that the Mamiya has a good home - just don't hold your breath...

[rondlg]

So we played about yesterday and just to close things for the record and I am convinced. What we have also decided that storing DNGs from RAW is probably not the way to go. To that end we are looking into workflows that include a step of generating a TIFF first and then creating a DNG from that for archival purposes.

Wish us luck and thanks for taking the time to help us out.

Regards

[snibgo]

Good stuff.

I've just noticed you said "I have ImageMagick v6.8.8-Q8". Q8 means it will ignore half the bits available from your Mamiya (which is, I think, 16 bits/channel/pixel). This may not matter much if you are making small JPEGs for on-line browsing, but certainly will matter if you are making copies for archive.