"NutsAboutVB" <d**@sms-networks.com> schreef in bericht
news:1146429789.090447.59650@j33g2000cwa.googlegroups.com...
> Hello,
>
> I am a VB.NET programmer and I have a JPEG image file (from digital
> camera) of about 109 KB's in size, when I open it and save it
> (without making any alterations at all, just going to File --> Save) in
> MS Photo Editor, the file is automatically shrunk in size to 81 KB's.
> When doing the same thing in MS Paint, the file is shrunk to 54 KB's.
> The file has the same number of pixels after both saves (as expected).
> My question follows...
>
> What are the 'automatic' changes that typical image editing
> software products perform to our images APART from any changes or
> alterations that we may make ourselves?
>
> I understand that one of these would be some form of compression (say,
> at 90) but I am unfamiliar with the other types of alterations that are
> made. When I compare the pixels in the original file and the new saved
> file (even without making changes, just opening & saving the file) I
> get completely different RGB values in each pixel. This is really bad,
> since (in my application) I need to be able to predict all typical (non
> explicit) changes made by graphics programs to normal images. So I have
> tried compressing the images via .NET code (EncoderParameters etc) at
> all possible values, 100, 99, 98 etc all the way down to 0 and I can
> not reproduce the exact pixel arrangements imposed by MS Photo Editor.
>
> My question is, why can't I, and what other types of transformations
> do I need to look into in order to try to replicate (and predict) such
> different pixel RGB values/arrangements imposed by various graphics
> programs? I don't know much about JPEG so not sure what
> ChrominanceTables and Luminance values are. The only thing I've tried
> altering is the Encoder.Quality parameter, and this accepts only
> parameter values between 0 and 100 of Long (Int64) data type. So in
> addition, can't I specify 89.5 or 94.3 (non integer) type values? Is
> this not in the JPEG spec to accept decimal values or is the .NET
> framework just limited in this way? Because I'm wondering, maybe
> these other software applications are specifying decimal fractions for
> the Quality setting of the encoder.
>
> So, in summary, just need to know...
> 1). What types of 'automatic changes' typically occur when an image
> is opened & saved using typical graphics programs?
> 2). If it is possible to pass non integer values floating point values
> (Single/Double/Decimal etc) for the Quality setting in the
> EncoderParameter object?
>
> I've had too many headaches because of this, Microsoft documentation
> is really bad, I understand my purposes may sound uncommon but I really
> need to be able to understand the types of automatic changes that are
> occurring, thank you in advance. I will respond promptly to all input,
> anything would be appreciated at this stage since I'm really empty
> direction wise.
>
> Thank you.
>