digital image distortion

  bpzoom 12:17 31 May 2007

Using a compact digital camera to photograph rectangular flat objects such as postcards, paintings or any document type objects, always produces an image where the borders of the image are no longer correctly rectangular. They lean inwards at one end. i.e. the top may be slightly narrower than the bottom or vice versa, or the same horizontally. The originals may be lying flat or propped up before the image is taken.It makes no difference. I have tried various programmes' (including high end programmes on trial) editing tools and none have worked. I believe this distortion is "normal" with digital cameras (?). Is there a cure please?

  Stuartli 13:59 31 May 2007

It's probably caused by the lens - the better the lens quality the superior the end result.

  hssutton 14:35 31 May 2007

This is caused mainly by not having the camera in perfect alignment with the photograph which results in parallax errors. The best way would be to buy a copying stand. click here

However if you're very careful and make sure the front element of your lens is perfectly square to the subject the error will be small and easily corrected

Depending on the degree oe parallax error this can easily be corrected using such as Photoshop.

Create new layer then go to "edit">>"Perspective" and adjust accordingly.

As Stuartli says, lens quality also plays an important part, but usually is easily corrected

  bpzoom 15:34 31 May 2007

Thank you both for your very helpful answers. I will get a copying stand, as I don't think I am capable of getting much better results without one, now that I have read the link. I have really tried with this. The images appear in an auction catalogue and the "leaning" is causing me concern. The camera is a compact Olympic digital, cost about £200. Many thanks again.

  Stuartli 18:26 31 May 2007

Another possibility would be one of the small tripods you can buy from places like 7DayShop for under £3 - I have one, it's beautifully made and cost just £2.50...:-)

You'd still need to have the image being captured square on though.

  David4637 19:08 31 May 2007

If you use Photoshop (version 7 onwards) or Elements you can easliy correct vertical or horizontal distortion. David

  bpzoom 22:08 31 May 2007

David, How? I have tried with the various tools in various programmes as well as Corel Draw free trial of version 11, and the tool which is supposed to correct this distortion made no difference. This was confirmed yesterday by a friend whose expertise is far greater than mine in this field and he has tried on an image I sent, only to admit defeat. One theory he offered is that if the image has already been cropped the tools don't work. Can I ask if a picture is being taken of a 3ft x 2ft painting for example, which is propped up in front of you, how do you know you are square on? The advantage of a framed picture is I can crop the frame and that cures this problem, but if the painting is not framed, then cropping the parallax fault encroaches onto the picture.

  bpzoom 22:18 31 May 2007

David, the tool in Corel Draw version 11 creates a rectangle or square box in the middle of your image. You drag the corners to where you want your corrected verticals and horizontals should be and click OK. Nothing happens. I repeated this with the help feature showing to make sure. Just thought I would say this in case you thought I had not tried properly.

  hssutton 22:34 31 May 2007

"Can I ask if a picture is being taken of a 3ft x 2ft painting for example, which is propped up in front of you, how do you know you are square on?"

Not only does it need to be "square on" the centre of the lens need to be in line with the centre of the painting (subject).

I left you instructions on how to correct perspective in photoshop in my first post, but cropping is then usually required, depending on how much correction you needed to make.

Most tripods have spirit levels built in (even the cheap ones)This will ensure you have the camera level, then you just need to align the centre of the camera lens to the centre of the picture, which you can hang on a wall.

  hssutton 23:12 31 May 2007

Here's a tutorial on how to correct perspective, using photoshop and PSP.
click here

click here

  David4637 18:47 01 Jun 2007

If you view the Photoshop link (I use PS)posted by hssutton, it explains very well how to correct vertical distortion. I have used it a number of times - it works OK. David

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