Re: Can't seem to get -level to work

On 2016-04-16 4:00 PM, Bob Friesenhahn wrote:
> On Sat, 16 Apr 2016, Toby Thain wrote:
>
>> Hi,
>>
>> I don't seem to understand the parameters of -level, or there is a bug?
>>
>> I want to adjust the black and white points by about 10%.
>>
>> Please see this image for the input and output of the parameters I'm
>> trying (I've also tried percentages, floating point, exchanging the
>> values, all to no avail):
>
> The documentation says that the syntax is
>
>     -level <black_point>{,<gamma>}{,<white_point>}{%}
>
> so
>
>     gm mogrify -level '10,1.0,90%' gradient-mod.tif
>
> should do what you want.

Yes, it seems to work.

So there may be a documentation bug, because the manual implies that 
gamma is optional. Based on the manual, as far as I can tell, my usages 
were correct in what if only 2 values are given, they are the black and 
white points. While the program seems to be interpreting the second 
value as gamma. Am I confused, or is the documentation wrong?

Thanks for the hint. I didn't think of trying the 3-value invocation.

>
> This usage seems to be based on a Photoshop dialog.

Yes, indeed I got my basis values from testing with Photoshop Levels.

--Toby

>
> Bob
>


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