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08.29.2007 at 12:51AM PDT, ID: 22793602

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6.6

Transparent watermark with Delphi 6

Zones: Graphics and Delphi Programming, Delphi Programming

Tags: delphi, watermark, transparent

Hi, Experts!

I have a JPG file and i want to add some watermarked text on it with transparent effect. I know how to work with JPG canvas and how to add some simple text, but i want to add trasnparent text (or maybe graphic object) on it and to control the visibility of it. Which methods are the best to do so?

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Question Stats

Zone: Programming

Question Asked By: Alexander_Savenko

Solution Provided By: ZhaawZ

Participating Experts: 2

Solution Grade: A

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08.29.2007 at 12:54AM PDT, ID: 19789397

Rank: Wizard

MerijnB:

use this: http://www.graphics32.org/wiki/

it has a little steep learning curve, but is very powerful and can achieve what you want.

08.29.2007 at 01:00AM PDT, ID: 19789415

Alexander_Savenko:

Thanks, but maybe there is any special lib/comp for that action?

08.29.2007 at 06:08AM PDT, ID: 19790777

Rank: Guru

ZhaawZ:

Here's how I would do it...

procedure AddWatermark(bmp: TBitmap; alpha: single; txt: string);
type
TLine = array [0..1023] of TRGBTriple;
var
wm : TBitmap;
src_x, src_y, dst_x, dst_y : integer;
dst, src : ^TLine;
begin
// create a watermark
wm := TBitmap.Create;
with wm, Canvas, Font do begin
PixelFormat := pf24bit;
Name := 'Courier New';
Size := 11;
Style := [fsBold];
wm.Width := TextWidth(txt) + 20;
wm.Height := TextHeight(txt) + 5;
TextOut(10, 5, txt);
end;
// put watermark on bmp
dst_y := bmp.Height - wm.Height - 10;
for src_y := 0 to wm.Height - 1 do begin
src := wm.ScanLine[src_y];
dst := bmp.ScanLine[dst_y];
dst_x := bmp.Width - wm.Width - 10;
for src_x := 0 to wm.Width - 1 do begin
dst[dst_x].rgbtRed := trunc(dst[dst_x].rgbtRed * (1 - alpha) + src[src_x].rgbtRed * alpha);
dst[dst_x].rgbtGreen := trunc(dst[dst_x].rgbtGreen * (1 - alpha) + src[src_x].rgbtGreen * alpha);
dst[dst_x].rgbtBlue := trunc(dst[dst_x].rgbtBlue * (1 - alpha) + src[src_x].rgbtBlue * alpha);
inc(dst_x);
end;
dst_y := dst_y + 1;
end;
wm.Destroy;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
jpg : TJPEGImage;
bmp : TBitmap;
begin
bmp := TBitmap.Create;
jpg := TJPEGImage.Create;
jpg.LoadFromFile('E:\05-28-07_1820370.jpg');
bmp.Assign(jpg);
jpg.Destroy;
bmp.PixelFormat := pf24bit;
AddWatermark(bmp, 0.5, 'i was here');
Canvas.Draw(0, 0, bmp);
bmp.Destroy;
end;

Accepted Solution

08.29.2007 at 06:18AM PDT, ID: 19790852

Alexander_Savenko:

ZhaawZ, thanks a lot, but please explain how to modify this to add watermark as multilines, another word, how to make it by line?

08.29.2007 at 07:07AM PDT, ID: 19791379

Rank: Guru

ZhaawZ:

>> please explain how to modify this to add watermark as multilines

Have a look at these lines:
with wm, Canvas, Font do begin
PixelFormat := pf24bit;
Name := 'Courier New';
Size := 11;
Style := [fsBold];
wm.Width := TextWidth(txt) + 20;
wm.Height := TextHeight(txt) + 5;
TextOut(10, 5, txt);
end;

This is where you "create" a watermark, i.e., a bitmap that will be placed on another bitmap. If you need multiple lines there, just make the height bigger and draw multiple lines. You may also load a bitmap from HDD instead of drawig text:
wm.LoadFromFile('E:\watermark.bmp');
wm.PixelFormat := pf24bit;

>> another word, how to make it by line?

Didn't get this one...

08.29.2007 at 07:14AM PDT, ID: 19791464

Rank: Guru

ZhaawZ:

If you replace

wm.Width := TextWidth(txt) + 20;
wm.Height := TextHeight(txt) + 5;
TextOut(10, 5, txt);

with

rect := ClipRect; // add "rect : TRect;" to variables
DrawText(Canvas.Handle, pchar(txt), length(txt), rect, DT_CENTER or DT_CALCRECT);
wm.Width := rect.Right + 20;
wm.Height := rect.Bottom + 10;
OffsetRect(rect, 10, 5);
DrawText(Canvas.Handle, pchar(txt), length(txt), rect, DT_CENTER);

you will be able to draw multiline text by calling

AddWatermark(bmp, 0.5, 'i was'#10'here');

08.29.2007 at 09:51AM PDT, ID: 19793055

Alexander_Savenko:

Thanks again, your gave most valueable example and comments!

08.29.2007 at 09:54AM PDT, ID: 19793091

Rank: Guru

ZhaawZ:

Glad to help ;)

08.30.2007 at 12:50AM PDT, ID: 19798127

Alexander_Savenko:

ZhaawZ, please help again! When i am trying to insert a picture as watermark i receive ScanLine index out of range!

08.30.2007 at 02:16AM PDT, ID: 19798486

Rank: Guru

ZhaawZ:

how big is the image you're trying to use as a watermark? and how big is the original image?

08.30.2007 at 03:14AM PDT, ID: 19798723

Alexander_Savenko:

i have different images to be watermarked with different sizes. Also it would be wonderfull if the watermarked image should be located in like "chess board" order!

08.30.2007 at 03:34AM PDT, ID: 19798784

Rank: Guru

ZhaawZ:

>> When i am trying to insert a picture as watermark i receive ScanLine index out of range!

This happens when you try to access the line with index less than 0 or more (or equal) than height of image. If all you can answer on my question is "I have different images to be watermarked with different sizes", this is all I can say about "index out of range" problem. It's like a general rule - if you have array of elements with indexes 0, 1, 2, 3, 4, you can't access an element with index 9, because there is no such element. Same with ScanLine. If you have lines with indexes 0, 1, 2, 3, 4, you can't access a line with index -1 or +9, because there is no such line.

>> Also it would be wonderfull if the watermarked image should be located in like "chess board" order!

Didn't get this one...

08.30.2007 at 03:55AM PDT, ID: 19798846

Alexander_Savenko:

Ok, thanks a lot

20080236-EE-VQP-29 / EE_QW_2_20070628