[VmX5]

So I've drawn pixels onto a bitmap using Bitmap.SetPixel() and I've checked the saved file using a photo editor to check if the correct ARGB values were drawn. But now the issue is when I try to read it some values are 1 or 2 off.

This is the function I wrote to translate image to text



These are the 2 pixels, they contain 4 chars each. (Enlarged ofc)


First Pixel : [76, 111, 114, 101]
Second Pixel : [109, 32, 105, 112]

But .Net would read:

First Pixel : [76, 110, 114, 100]
Second Pixel : [109, 32, 105, 112]

So is there something off with my code, or is there some other function I should use? or...? Yeah.

~VmX5

[+Haze]

Why reinvent the wheel? Why not just encode the Image to a base64 string?

[VmX5]

Why reinvent the wheel? Why not just encode the Image to a base64 string?

So in my previous versions of "Imext" I utilized the RGB values in a pixel but now I'm also trying to implement the Alpha value. So I need to be able to translate text into an image and back. But yea I got really stumped on this part :\

+Wheels are boring

[HFDone]

which image format you using
try to add 1 to r and b pixels and see if you still get wrong pixels

[Zilog80]

Point 1

I think you should change this:

PHP Code


<?php 
For Each rgbVal In rgbList
       returnString &= rgbVal.A.ToString & rgbVal.R.ToString & rgbVal.G.ToString & rgbVal.B.ToString
    Next 


for his one:

Code

rgbVal.A.ToString

will return "65" for alpha value = 65

but,

Code

C h r (rgbVal.A)

will retun "A" for alpha value = 65

Point 2

I made a fast bench. Here the results:

Code

...........Image      Marshal.Copy()    GetPixel()
i7-6700     2x1        2 ms              2 ms
i7-6700     200x100    1 ms              216 ms
i7-6700     400x300    6 ms              19352 ms

Code

............Image      Marshal.Copy()    GetPixel()
i5-M520     2x1        4 ms              3 ms
i5-M520     200x100    4 ms              687 ms
i5-M520     400x300    18 ms             38547 ms

The times measured how much time (in milliseconds) takes a a "TranslateImageToText()" function to complete.
As you can see, Marshal.Copy literally out-performs GetPixel() function.

I tried a 800x600 pixel image on my i7. Marshal.Copy() takes 29 ms, but GetPixel() takes ages: 427,287 ms, this is 7 minutes (and with a lot Garbage Collector memory allocations)

Point 3

You are right. I tried 2x1 pixel image with alpha + RGB values you posted. GetPixel() returns:

Code

Lnrdm ip

but, Marshal.Copy returs:

Code

Lorem ip

and i guess this is the correct behaviour.

Point 4

The source (you can check my SteganoNET here: https://github.com/kernelENREK/SteganoNE...Stegano.vb)

Spoiler (Click to View)
https://pastebin.com/1SSri2Sq


Point 5

The Benchs:

Spoiler (Click to View)





Hope it helps!

Edited
https://stackoverflow.com/questions/4124...-png-image

Seems there is a bug on Image.FromFile()
Just tested again like SO post said and GetPixel() return expected values

[VmX5]

Edited
https://stackoverflow.com/questions/4124...-png-image

Seems there is a bug on Image.FromFile()
Just tested again like SO post said and GetPixel() return expected values

Thanks for all the points! Your solution worked! :) Thanks! Would +rep again if could.

I never knew about Marshal.Copy... :\