Adjust varying brightness locally

S
Posted By
samkut
Mar 31, 2007
Views
331
Replies
3
Status
Closed
Hi there

After some searching on the web, I have not found the solution to the following problem:

I have some photographic images of paper documents with text on it (due to size, it has to taken by camera). As the paper is old and a little faded by the light, the paper is whitish to brownish: the color and brightness is changing depending on the position (darker where the paper was hit by light). The text is dark grey, almost black.

Ideally, I would like to convert the images into pure black and white images (not greyscale: black text on white background).

Is there a good tutorial how to achieve this? The procedure has to account for the changing local brightness and contrast. (Using a simple threshold will render some parts of the image black or white; you cannot find a appropriate threshold for the whole image.)

Help is very much appreciated

samkut at web.de

How to Master Sharpening in Photoshop

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LL
Lewis Lorton
Apr 1, 2007
wrote:
Hi there

After some searching on the web, I have not found the solution to the following problem:

I have some photographic images of paper documents with text on it (due to size, it has to taken by camera). As the paper is old and a little faded by the light, the paper is whitish to brownish: the color and brightness is changing depending on the position (darker where the paper was hit by light). The text is dark grey, almost black.
Ideally, I would like to convert the images into pure black and white images (not greyscale: black text on white background).

Is there a good tutorial how to achieve this? The procedure has to account for the changing local brightness and contrast. (Using a simple threshold will render some parts of the image black or white; you cannot find a appropriate threshold for the whole image.)
Help is very much appreciated

samkut at web.de
Why not post a link to a sample so viewers can try different techniques?
EH
Eugene Hurwitz
Apr 2, 2007
Experiment with filters. For example, a yellow filter will lighten yellowish to brownish areas on the paper, improving the contrast with the text. If you can, photograph in black & white.

"Lewis Lorton" wrote in message
wrote:
Hi there

After some searching on the web, I have not found the solution to the following problem:

I have some photographic images of paper documents with text on it (due to size, it has to taken by camera). As the paper is old and a little faded by the light, the paper is whitish to brownish: the color and brightness is changing depending on the position (darker where the paper was hit by light). The text is dark grey, almost black.
Ideally, I would like to convert the images into pure black and white images (not greyscale: black text on white background).

Is there a good tutorial how to achieve this? The procedure has to account for the changing local brightness and contrast. (Using a simple threshold will render some parts of the image black or white; you cannot find a appropriate threshold for the whole image.)
Help is very much appreciated

samkut at web.de
Why not post a link to a sample so viewers can try different techniques?
S
samkut
Apr 2, 2007
Why not post a link to a sample so viewers can try different techniques?

bw image (picture taken by camera in bw modus)
http://docs.google.com/Doc?id=dc6sj683_2f97825

color image
http://docs.google.com/Doc?id=dc6sj683_4gbmgwj

Sure, I will be able to fiddle with the light conditions; this will help a little. But still, the basic problem of locally varying brightness and contrasts remains….

Thanks for any help

sam

How to Master Sharpening in Photoshop

Give your photos a professional finish with sharpening in Photoshop. Learn to enhance details, create contrast, and prepare your images for print, web, and social media.

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