5 ms·
Why should it rotate, when it can use the standard method for notating the proper rotation? Your camera would be a lot slower if it had to rotate 16MP images b
by gfosco 14y ago
Why should it rotate, when it can use the standard method for notating the proper rotation? Your camera would be a lot slower if it had to rotate 16MP images between snaps.
- smackfu 14y agoOTOH, it has to rotate it for display on the screen, so it can't be that computationally bad.
- jstanley 14y agoNo it doesn't. The screen has the same orientation as the camera. When you hold the phone upside down, you are also holding the screen upside down ;)
- smackfu 14y agoRight, but when you look through your photos laters, it has to transform them so up is up on the display.
- pilif 14y agoBut when browsing through already stored pictures, a bit of delay is totally ok. Not so much when quickly showing some information overlaid over the picture you've just taken.
- deleted 14y ago[deleted]
- deleted 14y ago[deleted]
- nithinbekal 14y agoI suppose the device wouldn't bother with lossless rotation when displaying on the screen. When it comes to saving the image, it has to be lossless, which would probably take a lot more computation power.
- jstanley 14y agoI'm not sure what is referred to by "lossless" rotation in the case of axis-aligned orientation. I can't see how you can do a lossy rotation.
- nithinbekal 14y agoOh, sorry, my mistake. I've been looking around to see if ImageMagick could do rotation without degrading quality. (I'd also asked a question about that elsewhere in this thread.) So I assumed that most devices use something similar even for displaying on the screen. It appears I assumed wrong. :) I saw your other comment about axis-aligned rotation not being too computationally expensive. In that case, why aren't iPhones doing it by default? Wouldn't their computation power be comparable to that of most of the cameras that rotate the images? Or are cameras better equipped to handle such transformations?
- micampe 14y agoOther cameras don't usually rotate the photos (I've had to fix this same bug myself before the iPhone existed). My guess is that they didn't notice it earlier because photos from cameras are more likely to go through some post processing that on the final export saves the image with the data already rotated.
- micampe 14y agoBy decoding the jpeg, rotating the pixels and saving the jpeg again. I'm not even sure it makes sense to talk about lossy and losses when displaying images.
- objclxt 14y agoSomebody covered this further up, but in more detail: It is not the rotation itself that is the problem, but saving the resultant file. If you're working directly with the pixel buffer you only do a lossless JPG rotation if the image height and width are multiples of 8 (or 16, in some situations). This is because once you've performed the rotation you'll need to save the resulting output as a JPG, and unless your dimensions factor into the block size you'll need to recompute. This SO answer covers it in more detail[1]. However, if you're not working with the pixel buffer this doesn't apply. You can use jpegtran (part of libjpeg), for example, which manipulates the JPG file directly and never decodes it. Many basic image viewers and editors (like the Windows Picture Viewer, and probably the iOS Photos app but I'm not sure) don't use this approach though. [1]: http://photo.stackexchange.com/questions/12361/are-windows-photo-viewer-rotations-lossless http://photo.stackexchange.com/questions/12361/are-windows-p...