[SOLVED] Getting colour of an image?
lazarus / 39-Graphics

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Jishaxe · 2012-03-14 14:00

I have a square image that consists of one colour. Using
Lazarus/Pascal, how could I get the colour of said image in RGB format
(255;255;255)? A chunk of code I can steal/alter slightly would be
great, along with an explanation

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User137 · 2012-03-14 15:24

I suppose the wiki page answers to your question:
http://wiki.freepascal.org/Colors

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Jishaxe · 2012-03-15 06:39

Quote from: User137 on March 14, 2012, 04:24:52 pmI suppose the wiki
page answers to your question:
http://wiki.freepascal.org/Colors
I'm sorry, I may not have explained myself properly. I have an image
that i will load into my software. The image will be a square filled
in with a random colour. I wish to be able to "scan" the image from
within my program and have it detect what colour the square is filled
in with. If I need to pick a colour from a single pixel that is fine
because the whole square wil be the same colour.
Thanks!

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felipemdc · 2012-03-15 06:52

Just saying "Image" is far too generic. An image can be anything, it
could be a simple double array of colors, or it could be an object of
the class TBitmap, or an object of another class, or even TImage ...
you should specify what type you are using.

But suposing that you have a normal TGraphic descendent such as
TBitmap then you can use MyBitmap.Canvas.Pixels

See also the docs on TCanvas: http://lazarus-
ccr.sourceforge.net/docs/lcl/graphics/tcanvas.html

This will give you the color in the format TColor which can be
decomposed in the 3 channels using the routine RegGreenBlue:
http://lazarus-ccr.sourceforge.net/docs/lcl/graphics/redgreenblue.html

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Jishaxe · 2012-03-15 07:08

I'm sorry, I meant a non programmatic image. A file typically with an
extenion of .png or .jpg that contains a series of coloured pixels
that create a picture. Like an icon for an application, or a desktop
wallpaper.
I believe the class for this is TImage. I think this is a descendant
of TGraphic, so will I be able to use MyImage.Canvas.Pixels? (Can't
try, not on PC ATM) If so, does the image have to be drawn on the GUI?
Can I specify which pixel has the colour read from it?

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User137 · 2012-03-15 08:31

There is also Canvas.Colors[] array which in record format, giving you
r,g,b without using separate functions for it.

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felipemdc · 2012-03-15 09:12

TImage is a control to display static images, I don't recommend using
it for other tasks, although it will work. TImage does not descend
from TGraphic

If you just want to load a image from the disk and read it's colors,
use the appropriate reader class. I documented this here:

http://wiki.lazarus.freepascal.org/Developing_with_Graphics#Loading.2F
Saving_an_image_from.2Fto_the_disk

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User137 · 2012-03-15 09:43

(offtopic)
Would be nice to move Wiki focus to other formats more (PNG, JPG).
Nobody really uses BMP format anymore. Assuming that PNG's should be
first converted to TBitmap, makes them lose alpha channel.

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felipemdc · 2012-03-15 10:47

I did some changes to show that one can switch the classes at will

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Jishaxe · 2012-03-15 14:04

Okay, this is nice. So I can just load the image from file, call
MyBM.Canvas.Pixels.GetPixel(2,2), then get the colour with
RedGreenBlue(MyColor) and there we go? Asking for confirmation on here
again because I'm not on a computer and would like it sorted before I
get home

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felipemdc · 2012-03-15 14:28

Yes, only correction is that the syntax is:

var
  MyColor: TColor;
  lRed, lGreen, lBlue: Byte;
begin
  // ....
  MyColor := MyBMP.Canvas.Pixels[2,2]
  RedGreenBlue(MyColor, lRed, lGreen, lBlue);

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Jishaxe · 2012-03-15 15:42

Ah thanks a lot, this is great
Solved