Image quality setting Nikon D50 / photoshop results

BL
Posted By
brooke_lhernould
Nov 6, 2006
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476
Replies
9
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Closed
Working in Photoshop CS2 (Windows XP pro), I find that all my photos, regardless of the image quality setting in my Nikon D50 (JPEG normal, JPEG fine or RAW), have the same physical size and number of pixels when opened in Photoshop. There seems to be no difference in the quality of the image or number of pixels — all are at 17.2M pixel dimension, 3008×2000 pixels, 16.93 x 25,47cm at 300dpi.

I import photos from the camera into Picasa, then open them in Photoshop. In Picasa, there is a difference in size between the photos: 1.5mb for normal, 2.6mb for fine and 5.3mb for raw, but that disappears in Photoshop.

I’d appreciate an explanation of this, and advice as to how to maintain the image quality in Photoshop.

Thanks in advance.
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CC
Chris_Cox
Nov 6, 2006
The Quality setting for JPEG files determines how much detail gets thrown away, not how many pixels are saved.

And yes, because the detail is thrown away, the file size will differ.

And that doesn’t depend on the application at all.
BL
brooke_lhernould
Nov 6, 2006
Yes, I understand why there is a difference in file size before opening in Photoshop. What I want to know is why the photos all have the same size/pixel info when I open them in Photoshop, despite the fact that they were taken with a different image quality setting.
B
Bernie
Nov 6, 2006
Because they all have the same amount of pixels?
L
LenHewitt
Nov 6, 2006
Brooke,

despite the fact that they were taken with a different image quality
setting.<<

That doesn’t affect the number of pixels one iota, just the amount of JPG compression applied. So once the file is decompressed by opening it it will have exactly the same size in memory.
BL
brooke_lhernould
Nov 6, 2006
Thanks for your comment. I had thought that once a photo was taken with more jpeg compression (lower image quality setting), it had permanently lost some information. Is that not so? Are all photos from the same camera, then, of the same quality once they’re ‘decompressed’ by opening in Photoshop, regardless of the image quality setting when they were taken?

Is the image quality setting strictly a means of being able to fit more photos onto a memory card?

When I view photos in Picasa which were taken with different image quality settings, they do have a considerably different file size (5.3mb for raw down to 1.5mb for normal). What is the significance of that?

thanks again for your help!
C
chrisjbirchall
Nov 6, 2006
Are all photos from the same camera, then, of the same quality once they’re ‘decompressed’ by opening in Photoshop, regardless of the image quality setting when they were taken?

No. When you save a Jpeg, a huge amount of information (pixel detail) is thrown away. When you open a Jpeg, the program has to "invent" the missing pixels based upon the nearest adjacent pixels.

The result in Photoshop will be a file of the same Physical proportions (xxpixels x yypixels) as that originally captured by the camera. But the quality will not be the same because a lot of the information will be based upon a "best guess". Saving and reopening again will cause the quality to suffer even more.

Jpegs are an abomination. You should only really ever save a file as a Jpeg when it is destined for the web – where size does matter!

For the very best quality, shoot RAW. Open your files in Photoshop in 16 bit mode thereby preserving the full 12 bit capture of the original image. Then save it in a lossless format such as PSD or TIFF.

Chris.
BL
brooke_lhernould
Nov 7, 2006
Thanks so much, Chris. That explains a lot. One more question: how can I open files in Photoshop in 16 bit mode? My program always opens in 8-bit mode — can you tell me how to change that? Are there disadvantages?
Thanks again.
C
chrisjbirchall
Nov 7, 2006
At the bottom left of the ACR dialogue you will find options for the bit mode and colour profile.
BL
brooke_lhernould
Nov 7, 2006
Thanks again to all who helped with this question.

Brooke

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