Straightening Images

[Crazy Horse]

The post processing straightening methods I've looked at seem to use interpolation. Except when rotating 90, 180 or 270 degrees. (Is this correct?)

Has anybody noticed any discernable image degradation after horizon straightening?

Dave.

[Analog6]

I have not notices any image degradation, and it has to be done. Is there any other way to do it?

[Kym]

I have not notices any image degradation, and it has to be done. Is there any other way to do it?

Ideally level your camera when you take the shot.

The Pentax K-7 has a couple of new features ...
a) A horizon display in live view and the view finder which shows when you camera is level and tilt up to +/- 5 degrees

b) Auto horizon correction which is based on the in-body shake reduction and rotates the sensor

I use a and don't bother with b. What it does is reminds me to level the shot because its in you face.
Up until this feature I've always corrected in PS/LR with no degradation.
(Generally CCW - so I must have a natural tilt?? :confused013 )
Now I find I'm not having to correct in PS/LR as the image is straight.

So maybe get one of those spirit level jiggers that fit onto the hot shoe?
Eg. (Ebay) Spirit Level (http://cgi.ebay.com.au/3-Axis-Triple-3D-Bubble-Spirit-Level-on-Camera-Hot-Shoe_W0QQitemZ290353385157QQcmdZViewItemQQptZAU_Cameras_Photographic_Accessories?hash=item439a690ec5&_trksid=p3286.c0.m14)

[Crazy Horse]

I don't think there's any other way apart from getting the image straight in the first place.
Obviously the more times you rotate, distort etc. the more it will degrade. I was wondering if anyone had done so to a point where it was noticeable?

[Miaow]

I use Irfanview to straighten usually - And yes have to say have noticed the pictures probably are not a sharp after a slight adjustment as they were originally - this doesnt apply though to 90,180,270 etc.. Nothing overey major that a slight sharpen wont help with though

[Riverlander]

I have found the easiest way to straighten an horizon in Photoshop is to use the crop tool. A bit hard to describe in words only, but here goes.

Start the crop tool and click on the horizon line somewhere to the left
Drag the crop frame out to a reasonable size
Put your Pointer just outside one corner of the crop area until the curved arrow appears.
Turn the cropped area until one side runs along your horizon.
Resize the crop to the size and position you want.
Crop -- and the horizon will be level.

I can not say I have ever seen any degradation, but it is necessary to check your pixel per inch etc beforehand

[Bill44]

Basically the same as what Riverlander has just said, only I use Lightroom. Doing this to RAW does not have any degradation.

[dbax]

I use the little ruler tool under the eyedropper in CS3. Haven't noticed any image degradation.

[RuthJ]

I use the little ruler as well... no guesswork at all.

[Kodi]

Deleted by Kodi

[Seesee]

I either use the crop tool, free transform or if only a slight straighten the Arbitary control .....you should'nt get any loss of IQ with straightening an image....that is curious ?

The Nikon D300 has a grid reference in the viewfinder making keeping horizons straight much easier.

[ameerat42]

Good question. I do it all the time in CS2 and I've not thought about it only because I do very small changes. But it made m,e look into my references, and here's an answer - basically YES - from "Photoshop CS3 All in One Reference for Dummies" by Barabara Overmyer, Wiley 2007, P277 and on... Am...
"...• H% and V%: Increase the percentages to increase the Horizontal (H)
and Vertical (V) distortions.
• High Quality: Keep this option checked to enable Photoshop to use
a more detailed and complex algorithm when interpolating image

5. You can choose a second transformation type from the Edit Transform
submenu, if desired.
If you’re an ultraprecise type of person, you can also numerically transform
the selection by entering values on the Options bar.
In Figure 3-12, I executed all the transformations at the same time.
Be sure to execute all your transformations in one fell swoop if possible.
In other words, don’t scale a selection now and then five minutes later
rotate it and then five minutes later distort it, because every time you
apply a transformation to an image, you are putting it through an interpolation
process. You want to limit how many times you interpolate an image because it has a degrading effect — your image starts to appear soft and mushy.
Only flipping or rotating in 90-degree increments is interpolation free..."

[wideangle]

You can and do technically get loss of image quality when perspective correcting your images. It all depends on how much you have to straighten images. There is nothing like getting it all as right as possible there at the time of taking photos, but as you would be aware this isn't always possible due to the nature of lenses and looking upwards at subjects is going to create learning objects, so they need straightening. IQ loss is going to be the result of "pulling" your image so as to have straight verticals, like every method when PP images there is going to be loss in IQ

[ving]

i use PSP X2's image straightening tool... no problems with that :D

[jasevk]

I either use the crop tool, free transform or if only a slight straighten the Arbitary control .....you should'nt get any loss of IQ with straightening an image....that is curious ?

The Nikon D300 has a grid reference in the viewfinder making keeping horizons straight much easier.

:D stole the words out of my mouth! I've used this a few times, works brilliantly!