How to change the y axis scale in ImageView

[S Martin]

Hello,

I am trying to use ImageView to display an image but with axis included and specified y range.  Basically I'm doing something like this:

plt = pg.PlotItem(labels={'bottom':('time',''),'left':('frequency','')})

imv = pg.ImageView(view=plt)

x0, x1 = (0, 500)

y0, y1 = (0, 16)

xscale = (x1-x0)/img.shape[0]

yscale = (y1-y0)/img.shape[1]

imv.setImage(img, pos=[x0,y0], scale=[xscale, yscale])

plt.setAspectLocked(False)

Now the xaxis runs 0 to 500 left to right, but the yaxis runs 0 to 16 top to bottom.  However, I want the yaxis to start at the bottom at 0 and run to 16 at the top (a usual increasing y axis).  I am not sure how to set the axis range within ImageView.

Thanks,

Steve

[Patrick]

Hi,

This is some simplified parts from my code that I think does what you describe:

# Set up the plot and add the ImageItem

self.plot = self.plot_graphicsLayoutWidget.addPlot()

self.plot.showGrid(x=True, y=True)

self.plot.setLabels(bottom="Wavelength (nm)")

self.image = pg.ImageItem(np.zeros((1, 1)))

self.plot.addItem(self.image)

#...

# Acquire image from somewhere and set the ImageItem to use it

self.image.setImage(image)

# x-axis coordinate values are wavelengths (eg, 450--750)

# y-axis coordinates are simply the camera pixel numbers (0--199)

self.xlabels = np.arange(450, 750)

# Translate and scale the ImageItem to match the x-axis labels

self.image.translate(self.xlabels[0], 0)

self.image.scale((self.xlabels[-1] - self.xlabels[0])/len(self.xlabels), 1)

Patrick

[S Martin]

Thanks Patrick.

Your code certainly helps with over plotting an image on a plot region, but I am looking to use ImageView for its built-in functionality (ROI, histogram, etc...).  So, I'd like to reverse the y-axis labels within ImageView.

[Luke Campagnola]

You can use `PlotItem.invertY(False)` to set the direction of the y axis.

You might also need to use the `axes` argument to `ImageView.setImage()`, depending on the order of axes in your image data.

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[S Martin]

Ah, yes, PlotImage.invertY(False) worked!

Thanks!

Steve

On Thursday, May 3, 2018 at 12:10:27 PM UTC-4, Luke Campagnola wrote:

You can use `PlotItem.invertY(False)` to set the direction of the y axis.

You might also need to use the `axes` argument to `ImageView.setImage()`, depending on the order of axes in your image data.

On Wed, May 2, 2018 at 1:53 PM, S Martin <smar...@gmail.com> wrote:

Hello,

I am trying to use ImageView to display an image but with axis included and specified y range.  Basically I'm doing something like this:

plt = pg.PlotItem(labels={'bottom':('time',''),'left':('frequency','')})

imv = pg.ImageView(view=plt)

x0, x1 = (0, 500)

y0, y1 = (0, 16)

xscale = (x1-x0)/img.shape[0]

yscale = (y1-y0)/img.shape[1]

imv.setImage(img, pos=[x0,y0], scale=[xscale, yscale])

plt.setAspectLocked(False)

Now the xaxis runs 0 to 500 left to right, but the yaxis runs 0 to 16 top to bottom.  However, I want the yaxis to start at the bottom at 0 and run to 16 at the top (a usual increasing y axis).  I am not sure how to set the axis range within ImageView.

Thanks,

Steve

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