Sraightening photos is not benign

[michaelb]

I have always thought that straightening photos in PP was a very trivial matter, but apparently I was wrong.

I was working on an image recently an noticed that when I straightened the horizon (just a few degrees) the IQ was deteriorated.

I tried in both jpeg and TIFF formats, in PSP and Picasa - it didn't matter - the image was softer and detail was lost - not correctable with sharpening.

For a small print the loss of detail won't matter, but if your planning on doing big prints it might make a big difference. For my landscape work, it definitely matters.

I've always tried to get my images relatively straight in camera, but this will definitely change how I do things.

For those who are interested, this is my post on POTN on the subject....(contains image examples)...

http://photography-on-the.net/forum/showthread.php?t=587514

[Visual Reality]

Are you straightening before or after your resize? ANY action such as cropping, straightening, etc should be done with the full amount of pixels, before your resize. With enough pixels to work with this shouldn't be a problem and I haven't noticed that when working in Photoshop.

[Nickcanada]

Aren't you cropping your photos as you straighten them? I don't understand why you would notice any decrease in IQ by chopping bits off of the end of a photo and turning it?

Here is a quick test I did on one of my photos, done in LR

These are 100% crops.

http://i91.photobucket.com/albums/k320/livelifelivepics/IMG_8540-2.jpg

http://i91.photobucket.com/albums/k320/livelifelivepics/IMG_8540.jpg

[faisal]

I didn't know that...
I have always had problem with aligning my shots right....hmm...need to give it more importance now....

[michaelb]

Are you straightening before or after your resize? ANY action such as cropping, straightening, etc should be done with the full amount of pixels, before your resize. With enough pixels to work with this shouldn't be a problem and I haven't noticed that when working in Photoshop.


This was all done prior to resizing. I don't understand it but there definitely is a loss of IQ.

Here's the two images. Top is prior to rotation. These are 110% crops...

(look at the loss of sharpness and detail in the second image)...

http://brownphotography.smugmug.com/photos/397397830_evwSm-L.jpg

[michaelb]

Aren't you cropping your photos as you straighten them? I don't understand why you would notice any decrease in IQ by chopping bits off of the end of a photo and turning it?

Here is a quick test I did on one of my photos, done in LR

These are 100% crops.



yea, I don't get it either Nick. The amount that I rotated this image was only a few degrees, not enough to crop much out. And I got the same result in PSPX2 as in Picasa - what's the chance they both have the same problem?

[michaelb]

Someone on POTN explained it like this....

"Well, yes it's expected. Get a sheet of graph paper (your JPEG/TIFF/RAW file). Colour in one row of blocks with a highlighter. Now draw a line through it 10 blocks long, starting in the bottom right corner of the right-most block to the top left corner of the left-most block (a diagonal line across the 10 blocks). Then lay a second sheet of graph paper over it, along that line. You may have to hold it up to a window to see through the paper. When you go to "straighten" that original grid, what happens is that each "new" square on the line gets made up of partial colour values of the blocks it overlaps. So the new right-most square will be getting its value from the block that's all coloured; the new left-most square will be all white because it's shifted by a whole row. And the cells in between will be various shades depending on how much of the coloured block is included. So your nice, crisp line is now shaded (and twice as wide in the middle, because the same thing happens to the "new" squares above and below the line)."

[cdifoto]

110% crops make me cross-eyed.

[michaelb]

110% crops make me cross-eyed.

:D

For most wedding photogs this probably doesn't matter much but if I plan on making some big prints of my landscapes it really can impact the final image.

[Nickcanada]

I still don't understand. You are not creating another layer, it's like saying a picture will become less sharp if you tilt your head or tilt the monitor when you look at it.

What are your file dimensions before and after the tilt adjustment? it should change right? if it doesn't maybe your editing program is up-sampling or something?

I do see the loss of detail you are talking about but lets see some more samples... I don't see it in my own images when I adjust them.

[michaelb]

I still don't understand. You are not creating another layer, it's like saying a picture will become less sharp if you tilt your head or tilt the monitor when you look at it.


I don't think its that simple Nick - someone else explained it like this...

"I think of it this way: all the pixels are aligned to a perpendicular grid (and that will never change). The pixels in the original image are referenced to each other in perpendicular terms.

By rotating the image, you're throwing off that reference, and the software has to make corrections and compromises, to try to rebuild those references of the pixels to each other."





What are your file dimensions before and after the tilt adjustment? it should change right? if it doesn't maybe your editing program is up-sampling or something?

I do see the loss of detail you are talking about but lets see some more samples... I don't see it in my own images when I adjust them.

I checked the dimesions and they are changed. You would think that whatever image rotation algorithm is used would be common to most PP software, so I don't see why there would be a difference.

[Nickcanada]

I don't think its that simple Nick - someone else explained it like this...

"I think of it this way: all the pixels are aligned to a perpendicular grid (and that will never change). The pixels in the original image are referenced to each other in perpendicular terms.

By rotating the image, you're throwing off that reference, and the software has to make corrections and compromises, to try to rebuild those references of the pixels to each other."




I checked the dimesions and they are changed. You would think that whatever image rotation algorithm is used would be common to most PP software, so I don't see why there would be a difference.

With all the things we can do with an image it's crazy to think that something as simple as adjusting the horizon will degrade IQ. There has to be more to it.


I'm gonna do some 200% crops to prove you wrong. :D

I'll be back.

[talkingdog]

Thanks, good to know. I already have a hard time keeping my horizon, now I will try to be more careful. A self leveling sensor maybe +- 2-3 degrees would be nice.

[cdifoto]

With all the things we can do with an image it's crazy to think that something as simple as adjusting the horizon will degrade IQ. There has to be more to it.
Agree. I wouldn't be surprised if it's just PSP and Picasa having really poor algorithms.

I notice no degradation when I crop in Lightroom, nor Photoshop 7. But then again I don't look for it either.

[michaelb]

Agree. I wouldn't be surprised if it's just PSP and Picasa having really poor algorithms....

It might very well be, but I have been very pleased using PSP for the past 3 years or so. I can do 80-90% of what Photoshop can do.

I would hate to spend money on a new application just for image rotation....seems quite silly.


..
I notice no degradation when I crop in Lightroom, nor Photoshop 7. But then again I don't look for it either.

I don't normally look this closely for degradation either, but I was editing an image with mulitple layers and I was checking for degradation after each edit and amazingly only the straightening caused the problem.

[michaelb]

With all the things we can do with an image it's crazy to think that something as simple as adjusting the horizon will degrade IQ. There has to be more to it.


I'm gonna do some 200% crops to prove you wrong. :D

I'll be back.

Thanks Nick; I'm looking forward to seeing them.

[cdifoto]

I would hate to spend money on a new application just for image rotation....seems quite silly.
So would I. PSP at least (considering it's not free) should be good at rotation.

I can see the degradation in verse's samples by the way. I just have to look really hard since my laptop is high resolution for its size.

[Nickcanada]

PP in light room

http://i91.photobucket.com/albums/k320/livelifelivepics/_MG_7244.jpg

http://i91.photobucket.com/albums/k320/livelifelivepics/_MG_7244-2.jpg

http://i91.photobucket.com/albums/k320/livelifelivepics/_MG_7244-3.jpg

http://i91.photobucket.com/albums/k320/livelifelivepics/_MG_6447-3.jpg

http://i91.photobucket.com/albums/k320/livelifelivepics/_MG_6447-2.jpg

http://i91.photobucket.com/albums/k320/livelifelivepics/_MG_6447.jpg

I don't see a difference.

[faisal]

in the first one I see a difference...but not in the second one.....weird!!!!

[TenD]

I thought this was interesting but was skeptical. I use Lightroom also and I haven't ever noticed a difference either, but then again I wasn't looking for that either. I did a quickie in LR and just like in Nick's photos couldn't see anything. I used to be a PSP user, but had to switch to 100% LR recently with the switch to Mac.

[michaelb]

Nick - I agree with faisal - I can see some slight degradation in that first image, although the second looks about the same. By the way, love that second one Nick.

Do you have anything with text in it?

I chose this shot because it has text in it....

Original image....
http://brownphotography.smugmug.com/photos/397780670_66a7a-L.jpg



100% crops...

top is original, bottom after "straightening"...
http://brownphotography.smugmug.com/photos/397776765_tL2U8-L.jpg

[Mark_48]

I gave it a try in PSP X2. The image was straight from the camera as a JPG. No PP was done other than using the straightening tool to bring the guitar strings to horizontal. There does appear to be a slight difference if you look closely at the 4th string up where it crosses the bridge. It's either lighter in appearance or has lost some thickness. Maybe the entire straightened image looks overall lighter.

30D w/50mm f/1.4 @f/4

[michaelb]

Thanks for doing that Mark. My IQ degradation in the above example is certainly more obvious than yours; mine looks "lighter" as well, but its definitely softer too - I think the text shows it more clearly.

By the way, mine was shot RAW - converted to jpeg and then rotated.

[Nickcanada]

I didn't see any degradation in either set I posted.

Here is some text. ;)

http://i91.photobucket.com/albums/k320/livelifelivepics/IMG_7131.jpg

http://i91.photobucket.com/albums/k320/livelifelivepics/IMG_7131-2.jpg
http://i91.photobucket.com/albums/k320/livelifelivepics/IMG_7131-3.jpg


Sorry here ya go without the distraction...


http://i91.photobucket.com/albums/k320/livelifelivepics/IMG_7131-4.jpg
http://i91.photobucket.com/albums/k320/livelifelivepics/IMG_7131-5.jpg

[cdifoto]

I like that text, Nick.

[Nickcanada]

I like that text, Nick.

He he, here is another example. I like this one....

http://i91.photobucket.com/albums/k320/livelifelivepics/_MG_2310.jpg

http://i91.photobucket.com/albums/k320/livelifelivepics/_MG_2310-3.jpg

http://i91.photobucket.com/albums/k320/livelifelivepics/_MG_2310-2.jpg

[michaelb]

He he, here is another example. I like this one....



I agree Nick, these look fine to me. I just can't understand how the PSP X2 algorithm could be that different.

[Wesan]

Could it have to do with the jpeg-quality level you save the pictures at, after you have straightened them etc? It also looks like the straightened guitar picture has more noise reduction applied.

If the pixel references have to be rebuilt after straightening as previously described, maybe the change in image quality also could have to do with the resolution of the original picture?

Just some ideas, that might be incorrect... :o

[shoey]

By the way, mine was shot RAW - converted to jpeg and then rotated.
Have you tried rotating the Raw, then saving to jpeg?

[michaelb]

Have you tried rotating the Raw, then saving to jpeg?

PSP won't rotate RAW's, but I tried a TIFF file and got the same result. I'm at a loss to understand this problem.

[shoey]

Just tried in lightroom. It's a crappy photo but all i have at work.

100% crops, no editing at all, just imported cropped and exported.

[humbertklyka]

As mentioned before, there will always be degradation for any rotation apart from 90degrees. The quality difference will just depend on the actual algorithm used.

To compare output from different programs, I suggest for example rotating an image 15 degrees 24 times to be able to compare directly. (Or 6 times and then back to the right direction). This will clearly show which program uses better algorithms. I tried it with a photo of an orchid with Photoshop CS2 and you can clearly see the degradation, even though the difference was not that big for the first rotation.

An even worse example is using a test image with vertical lines one pixel wide, as shown in image 3. First the pattern was just rotated 15 degrees, and in image 5, the pattern is rotated 6 times, and basically all the detail is lost. (Images are shown in 2x size)

[Nickcanada]

okay that's cool. I guess it's a good thing most of us don't have to rotate an image 24 times or that we don't shoot lines exactly one pixel wide. :D

Seriously though, it's interesting stuff. There is more to straightening an image then I originally thought! :rolleyes: but honestly I think Michael is right by expecting more from his software. He's not doing anything extreme here.

[humbertklyka]

Hehehe, no my test cases are very theoretic fortunately :)

I fully agree that if the software lowers the image quality like that on a single rotation, something is strang and more should be expected from the software.

[michaelb]

humbertklyka -

Thanks for the examples - nicely done.

Considering all of the complex functions of PSP I am dissapointed with such a poor rotating algorithm.

[zmikers]

This is definitely interesting and makes me think twice about composing my shot (which we should do anyways). Thanks for the work you guys have put into this, it's very informative.

[Mark_48]

This would be a cheaper alternative to Adobe CS4.....
http://www.bhphotovideo.com/c/product/523871-REG/Canon_2377B001_EF_D_Focusing_Screen_for.html#featu res


I played around with CS3 today on a few images and it as well can mess up the pixels, but to a lesser degree than PSP. It seems to depend alot on how much of an angle it gets skewed from original.

[michaelb]

This would be a cheaper alternative to Adobe CS4.....
http://www.bhphotovideo.com/c/product/523871-REG/Canon_2377B001_EF_D_Focusing_Screen_for.html#featu res

....


I have one of those in my 5D, but not the 40D. It is helpful.

[zmikers]

That product looks very interesting. I'd like to give it a try.

[24Peter]

That product looks very interesting. I'd like to give it a try.

I paid three bucks for a spirit bubble level bubble that attaches to the hotshoe off ebay (something like this: http://cgi.ebay.com/TRIPLE-3-AXIS-BUBBLE-SPIRIT-LEVEL-ON-CAMERA-HOT-SHOE-3D_W0QQitemZ250307690961QQcmdZViewItem?hash=item25 0307690961&_trkparms=72%3A1417%7C39%3A1%7C66%3A2%7C65%3A12%7C 240%3A1308&_trksid=p3286.c0.m14) Great for tripod work, though degradation aside, I'm not afraid to rotate my images in CS3.

[Mark_48]

Some more research....

http://desktoppub.about.com/cs/graphicstips/qt/raster_rotate.htm


http://pcworld.about.com/news/Sep092003id112086.htm
Straighten the Horizon
There's nothing quite as distracting as a photo that's slightly crooked--whether it's the frame on the wall that's lopsided, or the horizon in the scene.
Luckily, you can straighten out a crooked picture in a heartbeat. Use your image editor's rotate tool (in Paint Shop Pro, it's Image, Rotate, Free Rotate) and specify how much to spin the picture. But be conservative: Most images are rarely off by more than a degree or two. And be aware that rotations introduce a bit of distortion, so you should avoid adding rotation to rotation. Undo and start again with a larger number if you didn't get it right the first time. I like the rotation tool in Photoshop Elements because you can grab a corner of the image and spin it with the mouse, stopping when it looks perfect. When you're done, crop the image to trim away the crooked sides.

Possibly more than you would ever want to know about rotational pixel distotion...
http://groups.google.com/groups?hl=en&q=%22paint%20shop%20pro%22%20rotation%20pixel%20di stortion&um=1&ie=UTF-8&sa=N&tab=wg


Michael, Other than the addition of the grid lines to the focus screen, is there any difference from the stock one?