[Digikam-users] Is jpeg rotation loseless?

Colin Guthrie kde at colin.guthr.ie
Sun Jun 11 23:47:04 BST 2006

Marcel Wiesweg wrote:
> You are using the image editor if you have opened the image in the image 
> editor, rotated, and clicked on save. The image editor is operating on raw 
> RGB data, and rotating there is no difference to applying any effect, it's 
> changing pixels. It can load from a variety of image formats, not only JPEGs, 
> it works on raw data, and it can save back to a variety of formats, some of 
> them are lossless (PNG, TIFF), but JPEG is not lossless.
> Lossless rotation is a special feature of the JPEG compression format, at a 
> level above raw image data.

Can the Image Editor tell that the image currently loaded has been 
modified by a user operation (e.g. effect etc.)? If so, could a feature 
be added to the Rotate option in the Image Editor that:

Checks to see if the image is unmodified, is a jpeg and the rotate 
amount is a multiple of 90 degs and if so, uses a lossless rotation of 
the raw image file and then reverts to that saved version (effectively 
reload the (now modified) saved image).

If the conditions are not met, the current rotating methods are used?

That would be kinda nice.



|     Colin Guthrie      |
| kde(at)colin.guthr.ie  |
| http://colin.guthr.ie/ |

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