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Date Posted: 07:43:53 05/03/00 Wed
Author: Michel
Subject: Re: Size of selection in Cms with zoom
In reply to: Jorge Neudorfer 's message, "Re: Size of selection in Cms with zoom" on 14:44:25 05/02/00 Tue


Hi Jorge,

It depends what you are trying to do.

Using,

GetDeviceCaps(ImageScrollBox.Graphic.DC,LOGPIXELSX)

gives the pixels per inch of the image on the screen. This will also be the same value even if the zoom is different. It is your screen resolution which depends on your video mode.

Using,

ImageScrollBox.Graphic.XDotsPerInch,

gives the pixels per inch of the image when it was probably scannned. This does not afect the way the image is displayed on screen. This is useful when printing an image, to print an image in its original size.

I think in your case what you need to do is use,

GetDeviceCaps(ImageScrollBox.Graphic.DC,LOGPIXELSX))

but also scale the value using your zoom percentage value.

Best regards,

Michel

> Can you helpme again.
>
> I do this now
> AnchoCms := 2.54 * (AnchoPixels /
> GetDeviceCaps(ImageScrollBox.Graphic.DC,LOGPIXELSX));
>
> I do this Before
> AnchoCms := 2.54 * (AnchoPixels /
> ImageScrollBox.Graphic.XDotsPerInch);
>
> I need to know cms when I make Zoom lens + or Zoom
> lens -
> on the image
>
> This an example with false data
>
> Zoom lens 100 %
> PixelsX = 160
> PixelsY = 180
> Width = 3.2
> Height = 3,6
>
> Zoom lens 120 % More pixels, same size
> Pixelxs = 180
> PixelsY = 200
> Width = 3.2
> Height = 3,6
>
> Zoom lens 80 % Less pixels, same size
> PixelsX= 140
> PixelsY = 160
> Width = 3.2
> Height = 3,6
>
> Why dont work ?
>
> >
> > Hi Jorge,
> >
> > What you are doing is correct. I guess what you are
> > missing is the "Resolution" to obtain physical
> > dimension.
> >
> > The window api calls,
> >
> > GetDeviceCaps(DeviceContext, LOGPIXELSX);
> > GetDeviceCaps(DeviceContext, LOGPIXELSY);
> >
> > Allow obtaining the resolution in pixels per inch for
> > a device context.
> >
> > If you are using a TDibGraphic, you can use the DC
> > property as the device context.
> >
> > Best regards,
> >
> > Michel
> >
> > > Hello to all, I need to know the size of a
> selection
> > > that I make on an image having in account the
> > > percentage of Zoom lens that exists on the image.
> > When
> > > the percentage is in 100 percent I do it of the
> > > following way
> > >
> > > Inches = pixels/ Resolution
> > > Cms = 2.54 * Inches
> > >
> > > Thanks for your help
> > >
> > > Please a need do this

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