[magick-users] smooter gradients

[Bob Meetin]

Sorry but I'm not familiar with what banding means.  I looked at your 
gradient. It looks good but if it were a little wider it would be easier 
to tell.  The version I'm running is whatever is available on the 
hosting server; the hosting company has it locked down so I cannot 
run/check convert via a shell command. 

For what it's worth, I made up a php script to create gradients.  See 
and compare results at:

www.dottedi.biz/tools/gradient_generator.php

What is being generated is/was not impeccably smooth.  I'm viewing it on 
a standard widescreen monitor at 1280x768 res.  However, I changed the 
monitor setting color quality from 16 to 32 bit and that makes a world 
of difference.  I'm not a hardware type - what would be the default 
setting of most monitors coming from the factory?

The .gif version which I'm seeing now is 'fair' quality but the .jpg and 
.png are much better.

-Bob


Ross Presser wrote:
> I think I spoke too soon.  While it's true that there is a 256 color
> limitation to GIF and that puts an upper limit on the smoothness, your
> result has definite banding. Like someone else who responded, I ran
> your command myself today with IM 6.3.3 04/20/07 Q16 and got this
> gradient:
>
> http://rpresser.googlepages.com/gradient.gif
>
> (yikes! Google says my site's bandwidth is exceeded. Oh well....
> suffice to say that the gradient is smooth to the limits of
> visibility.)
>
> Anthony's answer about color quantization is more likely correct. What
> version of IM are you using?
>
> On 7/18/07, Bob Meetin <ontheroad at frii.com> wrote:
>> Ross, That makes perfect sense. Here's a sort of related question.  I
>> was messing around this afternoon.  If I create a gradient from
>> white/black, white/red, they work fine, but if I do something extreme
>> like black/red, I end up with an almost rainbow-ish transition
>> sandwiched in between the black/red.  Any idea?  I can post to the group
>> list tomorrow.  -Bob
>>
>> Ross Presser wrote:
>> > GIF is limited to 256 colors (8 bits per pixel). You've specified a
>> > height of 600 rows. There is no way to get any smoother than what
>> > you've got.
>> >
>> > Try using PNG, or another 24 bits per pixel image format.
>> >
>> > On 7/17/07, Bob Meetin <ontheroad at frii.com> wrote:
>> >> I'm using the following to create a gradient:
>> >>
>> >> convert -size 10x600 gradient:#000-#fff gradient.gif
>> >>
>> >> It creates the image fine, but the transition is not smooth  See
>> >> sample at:
>> >>
>> >> http://dottedi.biz/codesamples/themes2/graphics/img.gif
>> >>
>> >> I used 100x600 in this sample to make it easier to visualize the
>> >> problem.  What option do I use to make this a smoother transition
>> >> gradient?
>> >>
>> >> -Bob
>> >>
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>> >>
>> >
>> >
>>
>>
>>
>
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