Perspective Correction

[Bryan]

I'm not sure if this is even the correct title, should perhaps be perspective manipulation?

 

There are times when you need to tilt the camera upwards to get a shot and the inevitable result is leaning verticals. I can't afford a dedicated shift lens, so the only remedy is to use the perspective cropping tool in PS. This is remarkably effective, and for minor infringements does a fine job, but there is some image deterioration particularly at the edges, which becomes quite noticeable if you go too far.

 

A number of questions here, first do others bother to correct at all? I know that the red top newspaper web sites use all kinds of images, some that I would not even consider uploading, so why be concerned?

 

Clearly you can use perspective to good dramatic effect, but I am talking here about run of the mill record shots of public buildings that the public expect to have vertical faces.

 

Secondly has anyone failed QC because of soft edges due to perspective correction, even though the centre is sharp?

 

Finally, it occurs to me that I could maybe use my Bronica film camera lenses with a shift adapter on the Sony NEX, if such a thing exists? Clearly they have an enormous image circle and could withstand a good deal of shifting on the APS sensor camera. (Probably not wide enough, the widest I have is a 50  )

 

[spacecadet]

I will hold the camera above my head if necessary bit I don't correct.

[Joseph Clemson]

I usually correct perspective using Lightroom, unless the building is very tall and narrow. I've never had a failure because of this. On the other hand I've no evidence to suggest that it has encouraged sales vis a vis images with uncorrected perspective, Like you I've noticed uncorrected images used in all kinds of publications, which makes me wonder if it's worth the effort to do the correction. I certainly wouldn't invest in a lens specifically to address the issue. I'll probably carry on correcting the perspective, simply because the images look 'right' when so treated.

[Joseph Clemson]

I will hold the camera above my head if necessary bit I don't correct.

How on earth do you keep the camera steady enough to avoid problems with sharpness due to camera shake? I find it hard enough to get a decent image using the viewfinder when shooting in typical UK overcast lighting conditions!

[Guest]

I shoot a lot of buildings and always correct, that's mainly for paid work so direct feedback from clients. I use tilts - mainly 17mm and 24mm but correct regardless using either LR or ACR, distort filter is also very useful at times.

 

BTW, you don't correct to 'vertical' - a few degress off actually looks better.

 

If you look at brochures or higher costs publications, you'll tend to see corrected work unless the image is to show a dynamic perspective.

[Armstrong]

I perspective correct in LR. I do pay very close to attention to the edges of the correction for sharpness. Sometimes there is not degradation and sometimes there is enough for me not to submit.

 

I have four images processed a few days ago which I need to look at with 'Fresh Eyes' regarding the effect of the PC. If I decide not to submit I'll still the submit the ones as shot.

[Niels Quist]

I will hold the camera above my head if necessary bit I don't correct.

 

How tall are you, Mark? 

 

 

BTW, you don't correct to 'vertical' - a few degress off actually looks better.

 

 

Thanks. Hadn't thought of this before unfortunately .... Will do, however.

[wiskerke]

I have two T/S lenses and still also correct the images in post.

However my best paid images and jobs are from/with uncorrected, sometimes wildly distorted images.

Take your pick.

 

wim

 

edit: and all what Philippe said.

[vpics]

I correct perspectives and my biggest sale ever is an images where I corrected the perspectives. 

 

There is a free programme for PCs called ShiftN and an architecture friend of mine swears by it.

As I'm on a Mac, I use DxO ViewPoint which works as a plug-in for Photoshop. 

[wiskerke]

+1 for DXO especially V2.0

 

wim

[Bryan]

I correct perspectives and my biggest sale ever is an images where I corrected the perspectives. 

 

There is a free programme for PCs called ShiftN and an architecture friend of mine swears by it.

As I'm on a Mac, I use DxO ViewPoint which works as a plug-in for Photoshop. 

 

ShiftN - Just tried it and it looks very good to me! Thanks 

[Inchiquin]

I correct perspective routinely. When shooting buildings with camera tilted upwards I try to allow extra space at the edges to prevent losing anything important when correcting.

 

Alan

[Ed Rooney]

I have two T/S lenses and still also correct the images in post.

However my best paid images and jobs are from/with uncorrected, sometimes wildly distorted images.

Take your pick.

 

wim

 

edit: and all what Philippe said.

 

Yeah, I use LR and DxO PC often, but I believe the general public is used to seeing wild distortion in images. It's common place. 

 

Flip through this coverage on the Mafia Capo's funeral in Rome by Il Messaggero. Have you ever seen so much inept crap in one place?

http://www.ilmessaggero.it/ROMA/CRONACA/casamonica_funerale_roma/notizie/1525456.shtml

[Bill Brooks]

I usually correct for perspective by making a vertical panorama in Photoshop.

 

Make the first tripod shot in your panorama a horizontal format shot at ground level almost straight on, but tilted up about 1 degree. All verticals should look good in this first shot except the top of the building will be cut off. Then tip the camera up and take a distorted second shot with at least a 40% overlap to the first. Do as many shots as necessary until you have covered the entire building.

 

The panorama feature in photoshop will use the first shot to line up the later shots, so you should have all your verticals in subsequent shots realigned correctly.

 

Crop your panorama to taste.

 

This method gives a better rendition than manipulating a single wide angle shot. There is some loss of sharpness in the last shot in the sequence, but that is mostly sky anyway. 

 

The first example is a panorama of 3 shots with the foreground of the first shot later cropped out. Everything sharp.

 

The second example is too many shots to count, resulting in some softness in the upper floors

 

 

[John Mitchell]

I only correct vertical perspective if I think that the effect is too dramatic. Usually, I don't bother. Obviously corrected buildings often look weird -- i.e. overstretched --  to me.

 

I too sometimes hold my camera above my head to reduce distortion. Tilting screens really help in this department.

 

Have never had a perspective corrected image fail QC.

[Robert Brook]

I mainly use the distort tool in PS. 

 

God, I hate the sterility of perfectly corrected images: there has to be some subtle distortion.  I want the subject or whatever to look like it is being perceived, seen from a point of view.  I often use subtle tilts as well.  But silly distortion I correct using distort, which is more versatile than standalone perspective correction.  I rarely see any images degradation that matters (D800).

[spacecadet]

That ShiftN does some humorous things sometimes. Might be good for a larf.

[John Mitchell]

I find that PTLens does a good job at correcting perspective. Shall check out ShiftN.

 

Personally, though, I like a little distortion. A perfectly straight world would be very boring.

[Bryan]

 

I usually correct for perspective by making a vertical panorama in Photoshop.

 

 

 

 

 

A nifty solution Bill, a good deal cheaper than a shift lens. Will try this one!

[John Mitchell]

Just downloaded ShiftN. Looks as it could be useful. Thanks.

[Tim Ayers]

When I'm out in the field (or city) I use the camera tilt indicators in my D800 viewfinder, but when I get back most pics seem to need up to a degree of rotation correction, then I will subtely correct for perspective in PS. I agree with Geoff that close to vertical can look more realistic and better. If more than mild perspective correction is required I don't submit the photo.

I would be interested to know if all this PhotoShop correction (rotation and perspective) is a recipe for loss of quality.

[Tim Ayers]

Just looked at my pics, to clarify - I do not submit if lots of perspective correction is required, unless I can submit without any correction at all. 

[wiskerke]

When I'm out in the field (or city) I use the camera tilt indicators in my D800 viewfinder, but when I get back most pics seem to need up to a degree of rotation correction, then I will subtely correct for perspective in PS. I agree with Geoff that close to vertical can look more realistic and better. If more than mild perspective correction is required I don't submit the photo.

I would be interested to know if all this PhotoShop correction (rotation and perspective) is a recipe for loss of quality.

 

That would be an easy test. I did exactly that this afternoon after using both DXO Viewpoint and the perspective crop in Photoshop. Conclusion: degradation was quite visible.

The general rule is to restrict resampling of the pixels in an image as much as possible. That means that an 'all in one go' filter like Viewpoint is better than consecutively controlling each single distortion. Actually doing all remapping like rotation, straightening and dimensions in the RAW developer is best.

 

How to test this? Take a (part of) the image straight out of the RAW developer and (a part of) the final image and load both in different layers. Alternate between the layers and view at 100 or 200%. Put small details as much as possible on top of each other. Do not use align, just keep the top image floating and drag.

Not all resampling is the same: Lanczos is usually better than Bicubic smoother or sharper or B-spline.

My guess is that a Photoshop plugin like Viewpoint does not come with it's own resampling algorithm. So Bicubic smoother or sharper it is. (Smoother for up; sharper for down-sizing.)

Does anyone know which algorithm DXO itself is using?

 

wim

[Robert Brook]

The point of a D800 is that images can take a lot of punishment and still the overall quality will be better than most DSLRs on the market.  Nowadays I rarely submit images that haven't had a lot of work done on them, but the kind of degradation I get is only really going to be of interest to pixel peepers.  What matters are the aesthetics.  Seems to be working since across agencies I sell well.

 

Usually when I make persective corrections I bring the image in at the bottom, rather than pull out at the top.  That helps to preserve quality.

[Bill Brooks]

 

When shooting straight upwards, the buildings can be so tilted that no correction is possible, but I'm OK with that because the intention is clear. I just hate it when buildings' walls (or trees) look a little slanting. As I said numerous times before: A "little bit" will always look like a flaw in photography.   

 

 

If you are using a perspective control lens on camera there is some image degradation as well. When shifted, a perspective control lens uses the edges of the lens image circle. The lens image circle edges are not as sharp as the centre. In addition you have to stop down below optimum sharpness aperture to avoid one sided vignetting on only the top part of your image. Circular objects near the image corners tend to go oval.

 

If you use the panorama technique the image degradation is tolerable because you are only using the sharper centre of the lens in each component shot. You then crop out the bad soft oval corners and downsize from a much larger final image.

 

Perspective control by any means will make tall buildings and mountains loom over the viewer. More majestic. Tilt the camera upwards with a wide angle lens to get everything in in one shot, and they tend to flatten and diminish in height.

 

 

I think Philippe said it well