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lossless image rotation question


90 image rotation is the most common operation. But is it lossless? Windows XP alerts it is not for its plugin, while ACDC has an option for "lossless jpg operations".

I wonder if PSP or PS have a jpg lossless 90 rotation. Is it sufficient to set the file size after the rotation equal or greater than the original?
Anybody knows?

Thank you
Claudio

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keithh 15 25.5k 33 Wallis And Futuna
25 Jul 2005 2:16AM
It's just XP having a hissy fit...don't worry, though I would always use PS to rotate anyway........just in case,,LOL
RichardB 14 328 United Kingdom
25 Jul 2005 2:34AM
My understanding is that it is not lossless.
The data will be compressed again by whatever quality setting you have set for jpeg compression. The same goes for other modification like cropping etc.
I have not tested it but it should be easy enough to find out. Open a jpeg image and a copy jpeg and rotate one again again and see if there is any difference.
I have done this with cropping in PS and it definately degrades the image. Crop a line of pixels off at a time and you will soon have a very degraded image.
conrad 14 10.9k 116
25 Jul 2005 3:10AM
Can anyone confirm or disprove what someone recently said to me, namely that rotation also makes objects in an image less sharp?

Conrad
RichardB 14 328 United Kingdom
25 Jul 2005 3:14AM
Confirmed - for the same reason as above.
I have just done a very quick test in PS7 - rotating an image and yes detail is noticeably lost after just a few rotations.
Only way to do it is to never work on JPEG files.
I am not sure of all the technical stuff perhaps someone else will know - but much depends also on the shape of your image if it is in the ratio 8x8, 16x16 etc then I believe the loss is insignificant other formats and the loss is greater.
keithh 15 25.5k 33 Wallis And Futuna
25 Jul 2005 3:17AM
Always rotate in C1 myself, but I've just rotated a duplicated image several times....and it looks like the original.
digicammad 16 22.0k 39 United Kingdom
25 Jul 2005 3:19AM
Richard when you say multiple rotations can you confirm exactly what you are doing. Are you saving and reopening between each rotation? Do you find the same if you have first saved the file as a PS file?

Ian
conrad 14 10.9k 116
25 Jul 2005 3:19AM

Quote:I've just rotated a duplicated image several times....and it looks like the original.


So does it depend on the program, then, or the file type?

Conrad
Just Jas 17 26.3k 1 England
25 Jul 2005 3:25AM
PSP8 +update to 8.10 has, I've recently noticed, a lossless rotation facility, which is listed away from the main rotation menu. However, I have not investigated it yet.

Perhaps the answer is a flat screen monitor which can be rotated through 90deg. Some do have this facility.

Useful for 'word' also!

jas
RichardB 14 328 United Kingdom
25 Jul 2005 3:30AM
What I did: made my save for the web quality setting to 50%, opened a JPEG, made a duplicate, rotated the duplicate 90degrees probably a dozen or more times, not saving just rotating again and again, and then looked at detail on a flower stamen at 100% size.
I realise this is extreme and not what would probably happen in reality but it was just to test the theory.
You would not get degradation of the image if you saved it as a psd of tiff file at the start, only in jpeg.
takui neko 15 849 11 Spain
25 Jul 2005 3:30AM
I just tried several rotations (5), using a double layered tiff file (non compressed), 16 bit, on PSCS2 and, by watching at the histogram and the amount of bits after saving, there is no difference at all.

Will try with a JPG file also...

Edit: No need for JPG experiment then... Smile
digicammad 16 22.0k 39 United Kingdom
25 Jul 2005 4:22AM
Interesting. Any image on which I intend doing any work, other than just tweaking curves etc, I save to PSD, so that must be why I don't see it.

Ian
skeletor 15 1.7k England
25 Jul 2005 7:17AM
I use this Rotate JPEG for lossless rotation of JPEGs. It's also free.
WOW skeletor, thank you a lot!! It's exactly what I was looking for!

Claudio

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