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BOOK: Visual Basic 2010 Programmer's Reference
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Old February 4th, 2012, 05:22 PM
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Question Changing selected pixels to a specific color

Hi Rod,

I've continued working on a project that you have helped me with before. I was wondering if you could give me some advice on a particular problem I'm having using pixels. I am working with images that will be a single solid color. They may be drawn and scanned or created in an image editing program. The files would be JPG files. I need to automatically change the single color to RGB (256,0,0,0). The back ground should not be changed. It will generally be white, but must not be the same color as the foreground image.

Perhaps code that would loop through all of the pixels and determine which ones would be a darker color and then change them to RGB(256,0,0,0) would work. Pure white would be RBG(256,256,256,256) I believe. Can you give me some insight on this one? As always, thank you for all of your great help. I've made a lot of progress on my application with you good advice and suggestions.


Old February 4th, 2012, 05:37 PM
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Note that if you have a jpg then the colors probably aren't exactly what you expect. Two pixels right next to each other may have RGB values 128, 128, 128 and 127, 129, 130. They'll look the same to you but if you're looking for exact color values, they won't match.

I think you'll need to loop through the image and examine each pixel to see if it is close enough to the target value and, if it is, replace it with a new value. To decide whether it is "close enough," you may want to add up the absolute values of the differences in the R, G, B components. (You could square them, add, and take the square root to get a Euclidean distance in RGB space but just adding should work and will be quicker and easier.

Yes 256,0,0,0 is black and 256,256,256,256 is white.

Rod Stephens, Microsoft MVP

Essential Algorithms: A Practical Approach to Computer Algorithms

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