IMatch allows you to rotate images directly from within thumbnail windows in steps of 90°. You can also mirror or flip an image. If you select multiple images, all images in the selection are rotated.
For lossless formats like TIFF, PNG or PSD, rotating an image does not impact the image quality.  Rotating JPEG files however may affect the image quality. Because JPEG is a "lossy" file format, re-saving JPEG files causes a small quality loss in the output image. You may or may not notice this decrease in quality. Re-saving JPEG files several times increase the typical JPEG artifacts in a way that they become visible, and hence the overall image quality decreases.
IMatch uses a special lossless algorithm that allows it to rotate JPEG images in steps of 90° without quality loss. The image is not recompressed during the rotation, but the image data itself is rotated within the image.
Limitations of Lossless JPEG Rotation
Although all rotations performed by this method are lossless in the sense that they can be reversed by rotating again in the opposite direction, JPEG images can be rotated without visual distortion only if their pixel dimension in the horizontal and/or vertical directions are evenly divisible by their corresponding block sizes (Minimum Coded Unit (MCU) in the JPEG jargon).
If a row or a column of an image must be manipulated during a rotation then the block size in that direction is subject to this restriction.
IMatch will automatically adjust these measures during the rotation process. This may cause the loss of up to 3 pixels in each dimension, but this is normally not noticeable.
The EXIF Orientation Flag
EXIF information generated by digital cameras contains an orientation flag. This flag indicates how the image should be rotated when displayed. IMatch optionally uses this flag to display images rotated. Since there are unfortunately many images around with an incorrect or invalid orientation flag (some applications rotate images without adjusting this flag), IMatch allows you to turn this feature off. |
