[gdal-dev] Contrast, Brightness and Gamma

[Chaitanya kumar CH]

Saâd,

Can you provide the vrt file and the commands you used?

On Thu, Mar 22, 2012 at 11:22 PM, Saâd HESSANE <saad.hessane at gmail.com>wrote:

> Hy Chaitanya,
>
> I applied a LUT to the VRT. It's work fine, and all pixel are between
> dst_min and dst_max.
> But why this is not work with the -scale parameter? The doc is clear :
> http://www.gdal.org/gdal_translate.html.
> "Rescale the input pixels values from the range *src_min* to *src_max* to
> the range *dst_min* to *dst_max*."
> Is it a bug?
>
>
>
> 2012/3/22 Chaitanya kumar CH <chaitanya.ch at gmail.com>
>
>> Saâd,
>>
>> It is better to have a combined LUT. It will save processing time and
>> data degradation.
>> Be informed that GDAL VRT is not specialized for this work. To get a
>> smooth curve as LUT, use some other graphics application that can handle
>> 16bit rasters.
>>
>>
>> On Wed, Mar 21, 2012 at 6:00 AM, Saâd HESSANE <saad.hessane at gmail.com>wrote:
>>
>>> Thank's all for your answers.
>>> I will use the LUT method, cause is the most right for me.
>>>
>>> Chaitanya said : "Gamma correction is more related to displaying the
>>> data than the data itself".
>>> Not in my case. I have to do this correction. But how to do that? Do i
>>> embed a VRT with a contrast correction LUT, in another VRT with a gamma
>>> correction LUT ? Or there is a method to declare LUTs in order to execute
>>> in the same vrt ?
>>>
>>> Thank's again !
>>>
>>>
>>>
>>> 2012/3/20 Brent Fraser <bfraser at geoanalytic.com>
>>>
>>>>  I like to use gdal_contrast_stretch from
>>>> http://www.gina.alaska.edu/projects/gina-tools/
>>>>
>>>> Usage: gdal_contrast_stretch <src.tif> <dst.tif>
>>>>   { { -linear-stretch <target_avg> <target_stddev> } |
>>>>     { -percentile-range <from: 0.0-1.0> <to: 0.0-1.0> } |
>>>>     { -histeq <target_stddev> } }
>>>>   [ -ndv <no_data_val> ]
>>>> Input must be either 8-bit or 16-bit.  Output is 8-bit.
>>>>
>>>> For example:
>>>>
>>>> gdal_contrast_stretch -percentile-range 0.02 0.98 input16bit.tif
>>>> output8bit.tif
>>>>
>>>> Best Regards,
>>>> Brent Fraser
>>>>
>>>>
>>>> On 3/20/2012 9:55 AM, Saâd HESSANE wrote:
>>>>
>>>> Hi list,
>>>>
>>>> I use gdal_translate to convert 16bits images to 8bits images. The
>>>> gdal_translate have the -scale argument to specify the convertion range
>>>> (source->destination).
>>>> If I change the destination range (dst_min and dst_max), I can do
>>>> manually a brightness correction (also a contrast correction).
>>>>
>>>> But is there any way to do that with a Photoshop like method?
>>>> For example set a brightness to -50, a contrast to +8 and let
>>>> gdal_translate do the job ?
>>>>
>>>> Also can I apply a gamma correction?
>>>>
>>>> I saw the VRT format and there's a way to apply a LUT. But I don't
>>>> think a LUT of 65536 values is the best way to apply the correction.
>>>>
>>>> Also the VRT have the scale ratio and scale offset elements. I think it
>>>> can be useful but I don't understand how use it...
>>>>
>>>> So simply put, my question : can I do a contrast, brightness or gamma
>>>> correction to a raster with gdal?
>>>>
>>>> Thank you !
>>>>
>>>> PS : I apologize for my broken English !
>>>>
>>>>
>>>> _______________________________________________
>>>> gdal-dev mailing listgdal-dev at lists.osgeo.orghttp://lists.osgeo.org/mailman/listinfo/gdal-dev
>>>>
>>>>
>>>
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>>
>>
>>
>> --
>> Best regards,
>> Chaitanya kumar CH.
>>
>> +91-9494447584
>> 17.2416N 80.1426E
>>
>
>


-- 
Best regards,
Chaitanya kumar CH.

+91-9494447584
17.2416N 80.1426E
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