RawImage data + Questions
lazarus / 39-Graphics

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benohb · 2011-09-27 01:48

Hello
Thanks to forum members

Question1:
Why always holds the first pixel value  183 In the 4 bytes ( Alpha) 
of bitmap..?



Code: [Select]procedure TForm1.Button1Click(Sender: TObject);

var FPixelsData: Pbyte;
ox :Integer;
bitm:tbitmap;
begin
   bitm:= tbitmap.Create;
   bitm.LoadFromFile('whiteImage.bmp');// 


  // PixelFormat from (any) to pf32bit //I did not find a way to
convert to 32 .. I used canvas
  bitm.Canvas.Rectangle(200,200,200,200);
  FPixelsData:=bitm.RawImage.Data;



 for  ox := 1 to  8 do begin  //rgba
       writeln('bayt[',ox,']',Byte(FPixelsData^));
       Inc(PByte(FPixelsData),1);
 end;




end;

Quote
bayt[1]255
bayt[2]255
bayt[3]255
bayt[4]183 <------------this Problem
bayt[5]255
bayt[6]255
bayt[7]255
bayt[8]0     <------------Correct value here, and all the remaining
bits...?


Note:
 I used  Image To read information only, without change it, to copy
data to  TFastBitmap
http://wiki.freepascal.org/Fast_direct_pixel_access


Question2:

When used ReAllocMem for size  largest memory 'Why does not the data
is saved in swap partition (linux)

If  i'am wrong in my information
Please .. How can I use (swap partition)

Question3:

 Is it possible to save a piece of memory , Example (RawImage.Data)
,and load it ,Without the use  other areas in the memory...?
Example;
pchar := pchar(RawImage.Data)
ReAllocMem(pchar,RawImage.sizeData); ///I know that this is
impossible(other pointer local ) only to clarify
Write(File.bak,pchar);


Note:
sys : linux
gui  : gtk2
cpu : i386
fpc  : 2.4.2-0 [2010/11/11]
lazarus :0.9.30

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User137 · 2011-09-27 11:18

Who says colors go from 0..255   If i recall the data for each R, G,
B, A has 65536 values, meaning it takes 8 bytes per pixel. (If you ask
me, color channel should always be 1 byte...) There are also some
functions that you can propably use to get detailed format info about
the rawimage. Actually something like
RawImage.Description.BitsPerPixel, RawImage.ReadChannels(rp,r,g,b,a)

When it comes to rawimages and BMP format, with my game engine i went
with just Canvas.Colors[]. BMP didn't follow the same rules that i
could use with JPG and PNG for rawimage.

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benohb · 2011-09-27 22:45

Code: [Select]Who says colors go from 0..255

Thanks for the answer..But in the my code Print each byte alone


Quotebayt[1]255 <- Red
bayt[2]255 <-Green
bayt[3]255 <-Blue
bayt[4]183 <-Alpha

in 32bit color Each channel color = 1 byte Means 4 byte (rgba)=
2^(8*4) = 4294967295 Probability And not 65536

Quotemeaning it takes 8 bytes per pixel

If the 8 bytes in each pixel will be a disaster 

I suppose you want to say in every 1 byte = 8-bit 
http://en.wikipedia.org/wiki/RGBA

QuoteActually something like RawImage.Description.BitsPerPixel,
RawImage.ReadChannels(rp,r,g,b,a)

is Always 32bit/4byte in pixel .......LCL  convert bitmap to 32 bit 
If you use canvas

General  .. problem Alpha in the first pixel does not stop my work..
Just to know is intended or bug

QuoteWhen it comes to rawimages and BMP format, with my game engine i
went with just Canvas.Colors[]. BMP didn't follow the same rules that
i could use with JPG and PNG for rawimage.
There is no JPG or PNG  Or even BMP in Memory image  ,only ...array or
Stringlist or  Block Memory
all data is Uncompressed ....   I speak to deal with the image ,as
especially LCL lazarus

Thank you