[cairo] scale without bluring

Michael Gurnett gurnett at glocalnet.net
Sun Sep 28 15:58:32 PDT 2008

This is what I'm getting

----- Original Message ----- 
From: "Antoine Azar" <cairo at antoineazar.com>
To: "'Michael Gurnett'" <gurnett at glocalnet.net>; <cairo at cairographics.org>
Sent: Monday, September 29, 2008 12:31 AM
Subject: RE: [cairo] scale without bluring

> Vlad's correct, I also tried about every mode in Photoshop (which has 
> great
> image scaling) and I get horrible results in every case. Check out the
> attached pictures for 3 different modes. Let us know if this is similar to
> what you're seeing with Cairo.
> I would recommend not scaling your image 99% but rather resampling your
> data. Although that might not work with your CPU and memory requirements.
> Otherwise, you could just append your new data to your original image
> (unscaled), and then rescaling to your desired size. You'd have good
> quality, but your original image would keep on growing in size in memory.
> Cheers,
> Antoine
> -----Original Message-----
> From: cairo-bounces at cairographics.org
> [mailto:cairo-bounces at cairographics.org] On Behalf Of Michael Gurnett
> Sent: Sunday, September 28, 2008 6:13 PM
> To: cairo at cairographics.org
> Subject: Re: [cairo] scale without bluring
> The data is such that individual spikes are not an issue. The graph is
> basically there so that the user can see the general behaviour of the
> currents and voltages of the machines. For a more detailed view the user 
> can
> monitor log files that save every second over a 72hr period (alot of 
> data).
> I have a moving data window that just shows the last lot of data, but 
> users
> do like to see entire data window as well. With the approach as was
> attempting here I get a constant behaviour in regards to how long the data
> processing takes and also a fairly small use of memory..
> Michael
> ----- Original Message ----- 
> From: "Vladimir Vukicevic" <vladimir at pobox.com>
> To: "Michael Gurnett" <gurnett at glocalnet.net>
> Cc: <cairo at cairographics.org>
> Sent: Sunday, September 28, 2008 11:57 PM
> Subject: Re: [cairo] scale without bluring
>> On Sep 28, 2008, at 2:41 PM, Michael Gurnett wrote:
>>>> I have to copy the old picture, To much data to redraw all over  again.
>>>> I'm
>>>> scaling down along the x-axis adding a a bit more data and then 
>>>> scaling
>>>> and
>>>> adding data and so on.
>> That's never going to give you a reasonable result, though -- you're
>> filtering the image each time you add data, and losing tons of data.
>> With either nearest neighbour or bilinear filtering, there'll be
>> something wrong... with nearest, it'll easily hide big spikes in your
>> data graph, if that column happens to be skipped due to rounding.   With
>> bilinear, it'll just blur your graph to nothing useful.
>>> Should I be using patterns instead. I've been using
>>>    cairo_set_source_surface (cr_buffer, surface_current, 0, 0);
>>>  cairo_paint(cr_buffer);
>> Shouldn't matter.  You should probably rethink the way that you're
>> rendering data.. for example, instead of rescaling for each data  point,
>> add in a new chunk at a time... e.g. maybe 25% of your total  width --
>> when you fill it up, compute averages of the previously  received data 
>> and
>> draw it into the first 75%, then start filling up  the new 25% using the
>> same average window.
>>    - Vlad
>>> ----- Original Message -----
>>> From: "Chris Wilson" <chris at chris-wilson.co.uk>
>>> To: "Michael Gurnett" <gurnett at glocalnet.net>
>>> Cc: <cairo at cairographics.org>
>>> Sent: Sunday, September 28, 2008 10:47 PM
>>> Subject: Re: [cairo] scale without bluring
>>>> On Sun, 2008-09-28 at 21:32 +0200, Michael Gurnett wrote:
>>>>> Have been struggleing with this for a while now and could do with 
>>>>> some
>>>>> pointers. I rescaling a graph by 0.99 over and over again in the x
>>>>> directions. When I do this the image blurs out and in the end the 
>>>>> data
>>>>> is lossed. I tried using StretchBlt but this just not seem to be
>>>>> compatible with the format of the cr. It doesn't blur but i doesn't
>>>>> scale correctly. I've tried turning off antialising but that does  not
>>>>> seem to help either. Any hints on how to scale without blurring.Is
>>>>> there a StretchBlt equivalent in cairo that I have missed?
>>>> You haven't mentioned it, so I assume you've not tried setting
>>>> CAIRO_FILTER_NEAREST on the source pattern. Although I have to ask, 
>>>> why
>>>> are you rescaling the graph and not redrawing?
>>>> -- 
>>>> Chris Wilson
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