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I want to make a figure that marker's size depend on the size of the figure. That way, using square marker size, no matter what resolution or figure size you choose, all the markers will touch each other, masking the backgroud without overlapping. Here is where I am at:
The marker size is specified in pt^2, with 1pt=1/72inch, the resolution in Pixel Per Inches, and the figure size in pixels (also the proportion that main subplot represent out of the main figure size : 0.8). So, if my graph's limits are lim_min and lim_max, I should by able to get the corresponding marker size using :
marker_size=((fig_size*0.8*72/Resolution)/(lim_max-lim_min))**2
because (fig_size*0.8*72/Resolution) is the size of the figure in points, and (lim_max-lim_min) the number of marker I want to fill a line.
And that should do the trick !... Well it doesn't... At all... The marker are so small they are invisible without a zoom. And I don't get why.
I understand this my not be the best way, and the way you would do it, but I see no reason why it wouldn't work, so I want to understand where I am wrong.
PS : both my main figure and my subplot are squares
Edit :
Okay so I found the reason of the problem, not the solution. The problem in the confusion between ppi and dpi. Matplotlib set the resolution in dpi, which is defined as a unit specific to scanner or printer depending on the model (?!?).
Needless to say I am extremely confused on the actual meaning of the resolution in matplotlib. It simply makes absolutely no sens to me. Please someone help. How do i convert this to a meaningful unit ? It seems that matplotlib website is completely silent on the matter.
If you specify the figure size in inches and matplotlib uses a resolution of 72 points per inch (ppi), then for a given number of markers the width of each marker should be size_in_inches * points_per_inch / number_of_markers points (assuming for now that the subplot uses the entire figure)? As I see it, dpi is only used to display or save the figure in a size of size_in_inches * dpi pixels.
If I understand your goal correctly, the code below should reproduce the required behavior:
# Figure settings
fig_size_inch = 3
fig_ppi = 72
margin = 0.12
subplot_fraction = 1 - 2*margin
# Plot settings
lim_max = 10
lim_min = 2
n_markers = lim_max-lim_min
# Centers of each marker
xy = np.arange(lim_min+0.5, lim_max, 1)
# Size of the marker, in points^2
marker_size = (subplot_fraction * fig_size_inch * fig_ppi / n_markers)**2
fig = pl.figure(figsize=(fig_size_inch, fig_size_inch))
fig.subplots_adjust(margin, margin, 1-margin, 1-margin, 0, 0)
# Create n_markers^2 colors
cc = pl.cm.Paired(np.linspace(0,1,n_markers*n_markers))
# Plot each marker (I could/should have left out the loops...)
for i in range(n_markers):
for j in range(n_markers):
ij=i+j*n_markers
pl.scatter(xy[i], xy[j], s=marker_size, marker='s', color=cc[ij])
pl.xlim(lim_min, lim_max)
pl.ylim(lim_min, lim_max)
This is more or less the same as you wrote (in the calculation of marker_size), except the division by Resolution has been left out.
Result:
Or when settings fig_ppi incorrectly to 60:
I'm trying to create a program, using Qt (c++), which can record audio from my microphone using QAudioinput and QIODevice.
Now, I want to visualize my signal
Any help would be appreciated. Thanks
[Edit1] - copied from your comment (by Spektre)
I Have only one Buffer for both channel
I use Qt , the value of channel are interlaced on buffer
this is how I separate values
for ( int i = 0, j = 0; i < countSamples ; ++j)
{
YVectorRight[j]=Samples[i++];
YVectorLeft[j] =Samples[i++];
}
after I plot YvectorRight and YvectorLeft. I don't see how to trigger only one channel
hehe done this few years back for students during class. I hope you know how oscilloscopes works so here are just the basics:
timebase
fsmpl is input signal sampling frequency [Hz]
Try to use as big as possible (44100,48000, ???) so the max frequency detected is then fsmpl/2 this gives you the top of your timebase axis. The low limit is given by your buffer length
draw
Create function that will render your sampling buffer from specified start address (inside buffer) with:
Y-scale ... amplitude setting
Y-offset ... Vertical beam position
X-offset ... Time shift or horizontal position
This can be done by modification of start address or by just X-offsetting the curve
Level
Create function which will emulate Level functionality. So search buffer from start address and stop if amplitude cross Level. You can have more modes but these are basics you should implement:
amplitude: ( < lvl ) -> ( > lvl )
amplitude: ( > lvl ) -> ( < lvl )
There are many other possibilities for level like glitch,relative edge,...
Preview
You can put all this together for example like this: you have start address variable so sample data to some buffer continuously and on timer call level with start address (and update it). Then call draw with new start address and add timebase period to start address (of course in term of your samples)
multichannel
I use Line IN so I have stereo input (A,B = left,right) therefore I can add some other stuff like:
Level source (A,B,none)
render mode (timebase,Chebyshev (Lissajous curve if closed))
Chebyshev = x axis is A, y axis is B this creates famous Chebyshev images which are good for dependent sinusoidal signals. Usually forming circles,ellipses,distorted loops ...
miscel stuff
You can add filters for channels emulating capacitance or grounding of input and much more
GUI
You need many settings I prefer analog knobs instead of buttons/scrollbars/sliders just like on real Oscilloscope
(semi)Analog values: Amplitude,TimeBase,Level,X-offset,Y-offset
discrete values: level mode(/,),level source(A,B,-),each channel (direct on,ground,off,capacity on)
Here are some screenshots of my oscilloscope:
Here is screenshot of my generator:
And finally after adding some FFT also Spectrum Analyser
PS.
I started with DirectSound but it sucks a lot because of buggy/non-functional buffer callbacks
I use WinAPI WaveIn/Out for all sound in my Apps now. After few quirks with it, is the best for my needs and has the best latency (Directsound is too slow more than 10 times) but for oscilloscope it has no merit (I need low latency mostly for emulators)
Btw. I have these three apps as linkable C++ subwindow classes (Borland)
and last used with my ATMega168 emulator for my sensor-less BLDC driver debugging
here you can try my Oscilloscope,generator and Spectrum analyser If you are confused with download read the comments below this post btw password is: "oscill"
Hope it helps if you need help with anything just comment me
[Edit1] trigger
You trigger all channels at once but the trigger condition is checked usually just from one Now the implementation is simple for example let the trigger condition be the A(left) channel rise above level so:
first make continuous playback with no trigger you wrote it is like this:
for ( int i = 0, j = 0; i < countSamples ; ++j)
{
YVectorRight[j]=Samples[i++];
YVectorLeft[j] =Samples[i++];
}
// here draw or FFT,draw buffers YVectorRight,YVectorLeft
Add trigger
To add trigger condition you just find sample that meets it and start drawing from it so you change it to something like this
// static or global variables
static int i0=0; // actual start for drawing
static bool _copy_data=true; // flag that new samples need to be copied
static int level=35; // trigger level value datatype should be the same as your samples...
int i,j;
for (;;)
{
// copy new samples to buffer if needed
if (_copy_data)
for (_copy_data=false,i=0,j=0;i<countSamples;++j)
{
YVectorRight[j]=Samples[i++];
YVectorLeft[j] =Samples[i++];
}
// now search for new start
for (i=i0+1;i<countSamples>>1;i++)
if (YVectorLeft[i-1]<level) // lower then level before i
if (YVectorLeft[i]>=level) // higher then level after i
{
i0=i;
break;
}
if (i0>=(countSamples>>1)-view_samples) { i0=0; _copy_data=true; continue; }
break;
}
// here draw or FFT,draw buffers YVectorRight,YVectorLeft from i0 position
the view_samples is the viewed/processed size of data (for one or more screens) it should be few times less then the (countSamples>>1)
this code can loose one screen on the border area to avoid that you need to implement cyclic buffers (rings) but for starters is even this OK
just encode all trigger conditions through some if's or switch statement
I'm using DirectWrite to render some text to a window. Everything seems to work except positioning when using different font sizes: I'd expect 2 texts with font size v1 and v2 and both with (x, y) = (0, 0) to be at the top left but as you can see:
neither "Test" nor "X" are really at the top left.
Is there a way to make this work?
Welcome to the world of fonts. Fonts are probably the most difficult thing to use, because there is surprises in font themselves ( there is so many new standards that supposed to solves everything and just confuse more because almost no font support it at 100%, even some 'classic' font have partial/bad information in them) the GDI, GDI+, DirectDraw don't draw font at the same position in pixels because of math, coordinate rounding, anti-aliasing... ( you can have one more bonus if you do the math with freetype ).
When you try to print the font there are other pb. So the only way around this is for me. Don't even try to draw font at certain pixel coordinates. Do your job at drawing font, picture, lines on the screen that render well, do your best to convert them to printing coordinate for exports but never expect to control pixel in fonts, everything is round approximates.
PS : Don't trust internal fields in fonts. On Arial they are good on all other fonts some are missing or initialised to zero, but the "fun" part it's not always the same field which are not present it depends of the fonts. You could only use the fields if you try them before by font. Yes fonts are fantastic!
The term #evilruff is referring to is called 'internal leading'. You can use IDWriteFontFace::GetMetrics or possibly IDWriteFontFace::GetDesignGlyphMetrics to get this value (for GetMetrics, the value you're looking for is most likely metrics.ascent - metrics.capHeight).
The values here are in Font Design Units, not pixels (of any sort). You can convert these values to em height by dividing by metrics.designUnitsPerEm; typically, font sizes in DirectWrite are specified by the pixel size of the (lowercase) m; so if you multiply the values in ems by the font size, you should get the values in pixels.
I'm assuming you are using an IDWriteTextLayout in conjunction with DrawTextLayout (rather than creating your own DWRITE_GLYPH_RUN). IDWriteTextLayout aligns glyphs to their layout cell (including the full ascent and line gap), not the glyph ink, and this is true of pretty much all text layouts, be they web browsers or word processors or simple edit controls. If they did not (instead aligning to the top of the letter), then diacritics in words like Ťhis would be clipped.
If you always want to align to the ink, create an IDWriteTextLayout, call IDWriteTextLayout::GetOverhangMetrics, and then call DrawTextLayout with an origin equal to negative DWRITE_OVERHANG_METRICS::left&top. If you want to align to the cap-height always (that way "hello" and "Hello" would both draw at the same vertical coordinate), then Eric's approach will work.
I'm drawing a color selection button and I'm looking for a nice and simple formula to get a good text color (foreground) for a given background color in RGB.
A simple try would be to just take the complement color but this will produce an odd looking button for colors like pure blue or pure red.
Is there something well known that does this?
If it matters at all, I'm using QT.
For maximum legibility, you want maximum brightness contrast without getting into hues which don't work together. The most consistent way to do this is to stick with black or white for the text color. You might be able to come up with more aesthetically pleasing schemes, but none of them will be more legible.
To pick between black or white, you need to know the brightness of the background. This gets a little more complicated, due to two factors:
The perceived brightness of the individual primaries red, green, and blue are not identical. The quickest advice I can give is to use the traditional formula to convert RGB to gray - R*0.299 + G*0.587 + B*0.114. There are lots of other formulas.
The gamma curve applied to displays makes the middle gray value higher than you'd expect. This is easily solved by using 186 as the middle value rather than 128. Anything less than 186 should use white text, anything greater than 186 should use black text.
I'm no expert on programming things related to RGB, but from a designer's perspective, often the most readable color will be just a much lighter (if the background color is dark) or darker (if the background color is light) version of the same shade.
Basically you'd take your RGB values and if they're closer to 0 (dark) you'd push them each up by an equal amount for your foreground color, or vice versa if it's a light BG.
Complement colors can actually be really painful on the eyes for readability.
Leverage an outline for legibility
If by "good text color (foreground)" you intend it for legibility purposes when the user chooses any background colour, you can always produce white text having a black outline. It will be legible on any solid, patterned or gradient background, from black through white and anything in between.
Even if this doesn't hit the mark of your intention, I think it worthwhile posted here because I came looking for similar solutions.
Building on top of Mark's response, here's some Ruby code that'll do the work
rgbval = "8A23C0".hex
r = rgbval >> 16
g = (rgbval & 65280) >> 8
b = rgbval & 255
brightness = r*0.299 + g*0.587 + b*0.114
return (brightness > 160) ? "#000" : "#fff"
You are better off with a high difference in luminosity. In general, colored backgrounds with colored text suck for readability, hurting the eyes over time. Lightly tinted colors (e.g. in HSB, S~10%, B>90%) with black text work fine, or lightly tinted text over a black background. I'd stay away from coloring both. Dark text (b~30%, s>50%) with a subtle coloration over a white background can also be fine. Yellow (amber) text on a deep blue background has excellent readability, as does amber or green on black. This is why old dumbterms (vt100, vt52, etc.) went for these colors.
If you really need to do color-on-color for the 'look', you could reverse both H and B, while pinning saturation at a moderate to low level.
And one last note: if you have a 50% gray background, rethink your interface. You're robbing yourself of half your dynamic range! You're alienating low-visibility users, including anyone over 35...
Color combinations often look terrible when not carefully chosen. Why not use either white or black for the text, depending on the Brightness of the color. (Will need to convert to HSB first.)
Or let the user choose either black or white text.
Or use pre-defined combinations. This is what Google does in their calendar product.
I've been looking for a simailr answer and came across this post and some others that I thought I'd share. According to http://juicystudio.com/services/luminositycontrastratio.php#specify the "Success Criterion 1.4.3 of WCAG 2.0 requires the visual presentation of text and images of text has a contrast ratio of at least 4.5:1" with some exceptions. That site lets you put in foreground and background colors to compute their contrast, although it would be helpful if it would suggest alternatives or ranges.
One of the best sites I've found for visualizing color contrast is http://colorizer.org/ It lets you adjust almost all manner of color scales (RGB, CMYK, etc.) at the same time and then shows you the result on the screen, such as white text on a yellow background.
I usually look at color complements, they also have color complement wheels to help
http://www.makart.com/resources/artclass/cwheel.html
If your color is HSL, flip the Hue by 180 degrees for a decent calculation
I wanted to put #MarkRansom's answer into use and managed to create this snippet:
I got the values From seeing how sRGB converts to CIE XYZ and built upon that.
The script simply tracks the position of the foreground item and it's position regarding the colored background items.
Then based on background luminosity it gradually changes the foreground text color to either black or white.
Open the codepen for full example
https://codepen.io/AndrewKnife/pen/XWBggQq
const calculateLight = (colorItem: number) => {
let c = colorItem / 255.0;
if (c <= 0.03928) {
c /= 12.92;
} else {
c = Math.pow((c + 0.055) / 1.055, 2.4);
}
return c;
};
const calculateLuminosity = (color: RGBColor) => {
return (
0.2126 * calculateLight(color.r) +
0.7152 * calculateLight(color.g) +
0.0722 * calculateLight(color.b)
);
};
const getContrastColor = (color: RGBColor) => {
if (calculateLuminosity(color) > LUMINOSITY_LIMIT) {
return FONT_COLOR_DARK;
}
return FONT_COLOR_LIGHT;
};
I thing that converting to HSV might be the way, but IMO changing hue would look weird. I'd try keeping the hue and fiddling with value and maybe saturation (light red buttons with dark red text ... hm sounds scary :-) ).
I am creating text editor using C. Can you explain these macros?
#define Ad (unsigned char far *)0xb8000000
#define Pos(y,x) (2*((y)*80+x))
#define Write(y,x,ch) *(Ad+Pos(y,x))=ch
#define WriteA(y,x,fb) *(Ad+1+Pos(y,x))=fb
Back in the dark ages of console programs, people used to output text by writing directly to the screen buffer.
The console screen buffer is organized as a continuous array of pairs of bytes, describing the displayed character and its attributes (color, background color, and eventually blinking).
In your case, the screen buffer seems to be at 0xb800000 (Ad). Pos translates a screen position (y,x) to a memory offset in the screen buffer, assuming a screen width of 80.
Write changes the displayed character at the specified position, while WriteA changes the character's color.
My goodness, it's like 1990 all over again...
Ad is the address of the section of memory which the video card (in text mode) maps onto its character generator. So if you write an ASCII 'A' to *Ad, then you'll get an 'A' at the top left of the screen.
Pos is a macro which calculates an offset from the top left of the screen for an x,y position. (It's a dangerously broken macro, because there are no () around the 'x'.)
Write writes a char to an (x,y) position
WriteA writes character attributes (color, etc) to an (x,y) position.
I don't want to be harsh, but you're going to struggle to write a text editor if you're struggling at this level.
You do not want to use them.
Those macros are for old hardware, where the screen could be accessed directly.
the first macro just specifies the base address of the screen (and far is not recognized by the Standard C)
the second macro converts a screen position to an offset
the 3rd one writes a character to the screen
the 4th one writes a colour to the screen
Again, you do not want to use those macros.
Ad return the address of the beginning of the video memory
Pos translate a x, y position into an absolute position in memory (assuming 80 chars width)
Write put the character ch at the x,y position
WriteA set the font color at the x,y position