Rotating jpegs with minimal or no loss, how to

SD
Posted By
Stu_D
Feb 27, 2004
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419
Replies
5
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Closed
My camera has an auto rotation feature that PS CS can sense. If the image is a vertical, it shows as a vertical in the browser.

However, the files are not rotated until one selects "apply rotation". When I use this feature, the files either get much bigger or smaller. For example, for a 1mb jpeg, the resulting rotated image could be 300kb, or 2mb. Apparently, there is a random jpeg compression setting happening each time. For example, if the camera jpeg setting was equivalent to 8 on PS, PS is now rotating it and jpegging it to around level 5 or 12. At 5, it’s discarding even more information, at 12, it’s recompressing it to a higher setting than the camera used, but it cannot gain additional info, so the size gets much larger without improving the quality.

Assuming PS cannot determine the jpeg compression level set by the camera, how can one set the closest setting used by the camera to get the maximum quality without adding too much to the size of the file? In other words, if the original file size is 1 mb, one can theoretically test resaving a copy of the file, and see what level of compression produces approximately the same size of file. But how does one set this in PS, as opposed to the program picking a random level?

I tried setting the level manually before doing rotations, and it doesn’t seem to pick up the last setting. Any method of setting this would be a great feature if one shoots hundreds or thousands of jpegs per shoot, and has to rotate them with minimal loss. Any ideas on how to do this, whether with auto rotation, or rotating several images at once in the file browser manually, would be appreciated.

Thanks in advance.

Stuart Dee

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Colin_Walls
Feb 27, 2004
Why do you want to rotate them and save as a JPEG?

Surely, if you are working on an image in PS, you won’t normally save that back as a JPEG, so all the loss issues are irrelevant.

A JPEG can be rotated with zero loss, so long as its dimensions are exact multiples of 16 pixels. There are lots of tools to do this [try Googling "lossless rotation"], one of which is Photoshop Album.

Guess it’s odd that PS CS doesn’t seem to support this.
SA
Sven-Martin_Adelhoff
Feb 27, 2004
Two ideas:

If you want to keep the same JPEG compression factor as your camera, try Save for the web. I think you can set a desired file size there, and PS chooses the compression factor accordingly.

BUT: If you open and resave a JEPG image, even with the same or a better compression factor, you will lose quality.

So, my second idea would be to use a tool for lossless JPEG rotation, which does not open the image. A lot of image viewers and album software do this.

Sven
SA
Sven-Martin_Adelhoff
Feb 27, 2004
Colin,

I guess it will be difficult for an image EDITING software to do a lossless JPEG transformation. An editing software as PS opens (and therby decompresses) the image. With the next saving, another compression is necessary, and quality is lost.

An image VIEWING software works on the saved (compressed) file directly, without decompressing it first.

Sven
CW
Colin_Walls
Feb 27, 2004
S-M A

I was thinking that the browser in PS behaves like a viewing program. Currently it just marks images for rotation, if you ask it to rotate. It would be nice if it could do a lossless rotate [as an option].
DM
Darian Muresan
Mar 7, 2004
Stuart,

You can also try Visere, which is a free image viewing program. It has LOSSLESS JPG rotation.

Best,
darian_at_dmmd_dot_net

wrote in message
My camera has an auto rotation feature that PS CS can sense. If the image
is a vertical, it shows as a vertical in the browser.
However, the files are not rotated until one selects "apply rotation".
When I use this feature, the files either get much bigger or smaller. For example, for a 1mb jpeg, the resulting rotated image could be 300kb, or 2mb. Apparently, there is a random jpeg compression setting happening each time. For example, if the camera jpeg setting was equivalent to 8 on PS, PS is now rotating it and jpegging it to around level 5 or 12. At 5, it’s discarding even more information, at 12, it’s recompressing it to a higher setting than the camera used, but it cannot gain additional info, so the size gets much larger without improving the quality.
Assuming PS cannot determine the jpeg compression level set by the camera,
how can one set the closest setting used by the camera to get the maximum quality without adding too much to the size of the file? In other words, if the original file size is 1 mb, one can theoretically test resaving a copy of the file, and see what level of compression produces approximately the same size of file. But how does one set this in PS, as opposed to the program picking a random level?
I tried setting the level manually before doing rotations, and it doesn’t
seem to pick up the last setting. Any method of setting this would be a great feature if one shoots hundreds or thousands of jpegs per shoot, and has to rotate them with minimal loss. Any ideas on how to do this, whether with auto rotation, or rotating several images at once in the file browser manually, would be appreciated.
Thanks in advance.

Stuart Dee

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