Compensation for aspheric and uneven illumination of flat images.

L
Posted By
liaM
Oct 8, 2007
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684
Replies
17
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Closed
Are there photoshop tools or other programs, which compensate for the curving of lines which occur when taking photos of flat images?

I’ve been using a copy stand to do this. Another problem which occurs, is the unevenness of the lighting. I imagine it would be possible to take a first picture of the surface of the copy stand platform using a white mat, and applying the resulting image to correct the unevenness. Is there a way to do this, too ?

liaM
novice learning Photoshop 5

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R
ronviers
Oct 8, 2007
On Oct 8, 6:23 am, liaM wrote:
Are there photoshop tools or other programs, which compensate for the curving of lines which occur when taking photos of flat images?
I’ve been using a copy stand to do this. Another problem which occurs, is the unevenness of the lighting. I imagine it would be possible to take a first picture of the surface of the copy stand platform using a white mat, and applying the resulting image to correct the unevenness. Is there a way to do this, too ?

liaM
novice learning Photoshop 5

Hi,
The Lens Correction filter, Filter>Distort>Lens Correction, may do what you’re looking for but I’m not sure when it was introduced. I only know that it is available in CS2.
You may be able to correct the lighting with a gradient overlay but it would probably be better if you corrected that with the actual lighting.
If you can post a link to a sample image I’m sure someone will give it a try.

Good luck,
Ron
P
pico
Oct 8, 2007
"liaM" wrote in message
Are there photoshop tools or other programs, which compensate for the curving of lines which occur when taking photos of flat images?
I’ve been using a copy stand to do this. Another problem which occurs, is the unevenness of the lighting.

Do it right in the first place and you won’t need Photoshop. We’ve been doing for a hundred years.

Use a slightly long lens (longer than the diagonal of the format). If you still get distortion, get a better lens.

Use even lighting.
Be happy.
L
liaM
Oct 8, 2007
pico wrote:
"liaM" wrote in message
Are there photoshop tools or other programs, which compensate for the curving of lines which occur when taking photos of flat images?
I’ve been using a copy stand to do this. Another problem which occurs, is the unevenness of the lighting.

Do it right in the first place and you won’t need Photoshop. We’ve been doing for a hundred years.

Use a slightly long lens (longer than the diagonal of the format). If you still get distortion, get a better lens.

Use even lighting.
Be happy.

The CCD is a 1/1.8 inch interline transfer CCD
(which I calculate having a 2 inch diagonal = 50mm)
The lens zooms between 8mm – 24mm. (The camera is a Pentax A30)

Now what 😉 ?
L
liaM
Oct 8, 2007
wrote:
On Oct 8, 6:23 am, liaM wrote:
Are there photoshop tools or other programs, which compensate for the curving of lines which occur when taking photos of flat images?
I’ve been using a copy stand to do this. Another problem which occurs, is the unevenness of the lighting. I imagine it would be possible to take a first picture of the surface of the copy stand platform using a white mat, and applying the resulting image to correct the unevenness. Is there a way to do this, too ?

liaM
novice learning Photoshop 5

Hi,
The Lens Correction filter, Filter>Distort>Lens Correction, may do what you’re looking for but I’m not sure when it was introduced. I only know that it is available in CS2.
You may be able to correct the lighting with a gradient overlay but it would probably be better if you corrected that with the actual lighting.
If you can post a link to a sample image I’m sure someone will give it a try.

Good luck,
Ron

Thanks.. I guess I shall have to investigate ($$ shudder) CS2. Is CS2 easier to use than version 5 ? Does it have a batch mode ?
GH
Gernot Hoffmann
Oct 8, 2007
liaM schrieb:

Another problem which occurs, is the unevenness
of the lighting.

Filter > Render > Lighting effects
is a powerful tool for the correction of lighting.

Best regards –Gernot Hoffmann
R
ronviers
Oct 8, 2007
On Oct 8, 8:13 am, liaM wrote:

Thanks.. I guess I shall have to investigate ($$ shudder) CS2. Is CS2 easier to use than version 5 ? Does it have a batch mode ?

I don’t know if it’s any easier since I have only used CS2 – I would guess about the same but more. CS3 is out now so you might want to look at that too. There is probably a plug-in for version five that will do what you are looking for – hopefully someone will tell you about it.
I am sorry to say that I don’t know what batch mode even is.
AM
Andrew Morton
Oct 8, 2007
wrote:
I am sorry to say that I don’t know what batch mode even is.

File->Automate->Batch perhaps?

Andrew
R
ronviers
Oct 8, 2007
On Oct 8, 10:16 am, "Andrew Morton"
wrote:
wrote:
I am sorry to say that I don’t know what batch mode even is.

File->Automate->Batch perhaps?

Andrew

I have noticed that but never looked into it. I have yet to do anything worth keeping much less a whole batch:)
R
Rob
Oct 8, 2007
liaM wrote:
pico wrote:

"liaM" wrote in message

Are there photoshop tools or other programs, which compensate for the curving of lines which occur when taking photos of flat images?
I’ve been using a copy stand to do this. Another problem which occurs, is the unevenness of the lighting.

Do it right in the first place and you won’t need Photoshop. We’ve been doing for a hundred years.

Use a slightly long lens (longer than the diagonal of the format). If you still get distortion, get a better lens.

Use even lighting.
Be happy.

The CCD is a 1/1.8 inch interline transfer CCD
(which I calculate having a 2 inch diagonal = 50mm)
The lens zooms between 8mm – 24mm. (The camera is a Pentax A30)
Now what 😉 ?

Its still not ideal to use a curved field lens to copy flat surfaces.
P
pico
Oct 8, 2007
"liaM" wrote in message

The CCD is a 1/1.8 inch interline transfer CCD
(which I calculate having a 2 inch diagonal = 50mm)
The lens zooms between 8mm – 24mm. (The camera is a Pentax A30)
Now what 😉 ?

Unless you have a ‘full frame’ digital camera it’s more likely your nominal-normal lens is 12mm. Use the 24mm setting. If you still get pincushion or barrel distortion (vertical lines bend in or out), then you might want to borrow a single-focal length lens (incorrectly referred to as a ‘prime’ lens.)

(Even so-called full-frame digitals aren’t quite that size because a peripheral area of the sensor is used for support circuits.)

So, rack it in to 24mm. Keep the focal plane parallel with the flat surface being copied. Use two lights, each at 45 degree angles and equal distance from the subject. That will get you there.
P
pico
Oct 8, 2007
"Rob" wrote in message

Its still not ideal to use a curved field lens to copy flat surfaces.

🙂 All lenses are curved. He should do okay without such.
L
liaM
Oct 8, 2007
pico wrote:
"liaM" wrote in message

The CCD is a 1/1.8 inch interline transfer CCD
(which I calculate having a 2 inch diagonal = 50mm)
The lens zooms between 8mm – 24mm. (The camera is a Pentax A30)
Now what 😉 ?

Unless you have a ‘full frame’ digital camera it’s more likely your nominal-normal lens is 12mm. Use the 24mm setting. If you still get pincushion or barrel distortion (vertical lines bend in or out), then you might want to borrow a single-focal length lens (incorrectly referred to as a ‘prime’ lens.)

(Even so-called full-frame digitals aren’t quite that size because a peripheral area of the sensor is used for support circuits.)
So, rack it in to 24mm. Keep the focal plane parallel with the flat surface being copied. Use two lights, each at 45 degree angles and equal distance from the subject. That will get you there.

Mega Thanks, Pico !
R
Rob
Oct 8, 2007
pico wrote:
"Rob" wrote in message

Its still not ideal to use a curved field lens to copy flat surfaces.

🙂 All lenses are curved. He should do okay without such.

I’m talking about fields.
U
usenet
Oct 9, 2007
liaM wrote:

Are there photoshop tools or other programs, which compensate for the curving of lines which occur when taking photos of flat images?
I’ve been using a copy stand to do this. Another problem which occurs, is the unevenness of the lighting. I imagine it would be possible to take a first picture of the surface of the copy stand platform using a white mat, and applying the resulting image to correct the unevenness. Is there a way to do this, too ?

Take a better picture in the first place: Use the longest zoom setting that produces the least pincushion effect. Put the material on a stand. Put the camera on a tripod. Get some better lighting, even just work lights, and experiment with angles, though straight-on will work best for the lights. I’d say use a flash gun, if it’s at all possible. Use the histogram to get a good exposure (using manual mode, or EV compensation if that’s not available.)

To get rid of the lens distortion: Hugin. It’s free. Take an image of graph paper or a brick wall or some other flat surface with lot of straight lines. Tweak it in Hugin to get the lines straight again and undistorted. Now process the pictures you took using the same settings in Hugin.

HTH.


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P
pico
Oct 9, 2007
"Rob" wrote in message
pico wrote:
"Rob" wrote in message

Its still not ideal to use a curved field lens to copy flat surfaces.

🙂 All lenses are curved. He should do okay without such.
I’m talking about fields.

Just giving you grief. Fields it is!
P
pico
Oct 9, 2007
Can’t you use a scanner for this? Or is the object too large?
L
liaM
Oct 9, 2007
Paul Mitchum wrote:

To get rid of the lens distortion: Hugin. It’s free. Take an image of graph paper or a brick wall or some other flat surface with lot of straight lines. Tweak it in Hugin to get the lines straight again and undistorted. Now process the pictures you took using the same settings in Hugin.

Very interesting.. Hugin would seem ideal for copy stand photography of flat pages (with a vacuum table.. which I have rigged up) in front of a bay window facing north for the light..

What would you think if, when using Hugin, I use a wide angle.. the advantage of which is depth of field tight focus?

Hugin would correct the spherical distorsion and I’d get the best focus available from my camera. There must be a catch 😉 !

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