How to save a .GIF - "interlaced" ?

[Mads Aggerholm]

Hello Sirs,

I am having a BMP loadet into a picturebox. This I'd like to save on
my harddisk as a GIF:

picturebox1.Image.Save("C:\\DATA\\PICTURES\\testpi c.gif",
ImageFormat.Gif);

However, this GIF-file is not in very good quality.

Using "Irfanview", I can change a BMP-file to GIF in quite better
quality setting an option called "save interlaced".

How am I going to do that using C#?

I have allready tried:

EncoderParameters encparams = new
EncoderParameters(1);
encparams.Param[0] = new
EncoderParameter(System.Drawing.Imaging.Encoder.Co lorDepth, 256L);
ImageCodecInfo[] imcodecinfo =
ImageCodecInfo.GetImageEncoders();
picturebox1.Image.Save(("C:\\DATA\\PICTURES\
\testpic.gif", imcodecinfo[0], encparams);

and more of the kind: Encoder.Compression, Encoder.Quality, etc.

This actually solves the problem, no matter what value I put after the
Encoder."something": (16L, 32L, 256L - why the "L" by the way??)

The only problem here is, that this GIF-file i about 7 times as big as
nessasary.
The GIF file saved with the "ImageFormat.Gif" is 24 Kb.
The GIF made with Irfanview interlaced is 56 Kb (and this has the
quality I need).
Using these EncoderParameters, the GIF ends up being 359 Kb.

This is a problem! By different reasons it is important that the files
are as small as possible, and I have to use GIF.

The fact that Irfanview can do this, tells me it can be done.

Can anybody in here tell me how?

Thank you very much in advance.

Sincerely / Best regards
Mads Aggerholm

[Peter Duniho]

On Mon, 09 Jun 2008 23:32:58 -0700, Mads Aggerholm
<ma************@gmail.comwrote:

I am having a BMP loadet into a picturebox. This I'd like to save on
my harddisk as a GIF:

picturebox1.Image.Save("C:\\DATA\\PICTURES\\testpi c.gif",
ImageFormat.Gif);

However, this GIF-file is not in very good quality.

Using "Irfanview", I can change a BMP-file to GIF in quite better
quality setting an option called "save interlaced".

How am I going to do that using C#?

Interlaced has nothing to do with image quality. It simply controls
whether the scan lines of the image are stored sequentially or not. When
the image is interlaced, then an image being downloaded can be presented
in a usefully partial way before the entire download has completed.

In theory, you could probably control this with the Encoder.ScanMethod
encoding parameter. But a) it would have no effect on your image quality,
and b) if I read the docs right, it's not currently supported in .NET
anyway.

I admit, it's hard to know whether I'm right about the latter point. The
docs regarding image encoding for .NET are surprisingly useless. :)

[...]
This actually solves the problem, no matter what value I put after the
Encoder."something": (16L, 32L, 256L - why the "L" by the way??)

The only problem here is, that this GIF-file i about 7 times as big as
nessasary.
The GIF file saved with the "ImageFormat.Gif" is 24 Kb.
The GIF made with Irfanview interlaced is 56 Kb (and this has the
quality I need).
Using these EncoderParameters, the GIF ends up being 359 Kb.

Again, hard to say given how impossibly vague the documentation is, but
what happens when you use 24L instead of 256L? A bit-depth of 256 bits
per pixel would certainly result in a much larger file. :)

By the way, the L tells the compiler to make the argument an Int64, aka
"long". Why the color depth encoder parameter needs to be specified as a
"long", I don't know, but I did see other examples doing it that way, so
why rock the boat? Again, if the docs weren't so vague, I'm sure they'd
explain that (or else explain that the argument could in fact just be a
regular "int").

If using a more reasonable color depth doesn't change the behavior, then I
don't know. Without a concise-but-complete code sample, along with a
single image file posted somewhere that it can be downloaded for use with
the code example, it's not really possible to say. For all we know, the
problem is as simple as you not actually emitting an image file of
different pixel dimensions from your program as in the image conversion
program (either because you start with different-sized images, or because
the output is specifically created as different sizes).

Pete

[Mads Aggerholm]

Hi Pete,

Thanks for your reply.

Again, hard to say given how impossibly vague the documentation is, but *
what happens when you use 24L instead of 256L? *A bit-depth of 256 bits *
per pixel would certainly result in a much larger file. *:)

I don't have a "bit-depth". I have colordepth, which I tried to set to
24L. No change in size.

If I look at the proberties of the "interlaced" gif-file, it says it
has a bit-depth of 8.
"My" gif file, saved with the encoding, has a bitdepth of 24. No
matter what I do.

Does my encoding-part do anything at all?? The result is always the
same, no matter what I change??

By the way, the L tells the compiler to make the argument an Int64, aka *
"long". *Why the color depth encoder parameter needs to be specified as a *
"long", I don't know, but I did see other examples doing it that way, so *
why rock the boat?

Thanks for the explanation and you suggestions.

Sincerely / Best regards
Mads Aggerholm

[Mads Aggerholm]

Hello again.

Now it seems to work.
I was a little puzzled about _nothing_ changed whatever I did.
This made me make this change:

picturebox1.Image.Save(("C:\\DATA\\PICTURES\\testp ic.gif",
imcodecinfo[1], encparams);

Please note the number [1] instead of the [0] following the
"imcodecinfo".
Now I have a GIF on 48 Kb with fine quality.

Problem solved!

Sincerely / Best regards
MadsAggerholm

[Peter Duniho]

On Tue, 10 Jun 2008 03:47:39 -0700, Mads Aggerholm
<ma************@gmail.comwrote:

Hello again.

Now it seems to work.
I was a little puzzled about _nothing_ changed whatever I did.
This made me make this change:

picturebox1.Image.Save(("C:\\DATA\\PICTURES\\testp ic.gif",
imcodecinfo[1], encparams);

Please note the number [1] instead of the [0] following the
"imcodecinfo".

Well, yes. It would be imperative that you use the correct encoder. :)

Actually, most code I've seen enumerates that list to find the appropriate
encoder, rather than just picking one at random. You might want to do
that, rather than just assuming that the one you want is in the 1st (or
0th) position.

Sorry I didn't mention that earlier...I got distracted trying to figure
out why MSDN is so lame about documenting all this stuff.

Pete

[Olivier Montiel]

Hello, i carefully read your last post talking about the GIF parameters and I cannot find the right expression to save my picture as a GIF file with good quality.

Could you post your code here ?

Thanks in advance

[Olivier Montiel]

Hello, i carefully read your last post talking about the GIF parameters and I cannot find the right expression to save my picture as a GIF file with good quality.

Could you post your code here ?

Thanks in advance

[Anthony Jones]

"Olivier Montiel" wrote in message news:20*****************@free.fr...

Hello, i carefully read your last post talking about the GIF parameters
and I cannot find the right expression to save my picture as a GIF file
with good quality.

Could you post your code here ?

See:-

http://support.microsoft.com/kb/319061

--
Anthony Jones - MVP ASP/ASP.NET