Re: batch process jpegs

[Joel Roth <joelz@pobox.com>]

mick crane wrote:
> I've got a bunch of jpgs from the camera where the bits I want are a bit
> underexposed. What I'd like is a GUI that will batch process them.
...
> Any suggestions for available GUI that will batch process jpgs ?

Hi Mick,

I would suggest using the command line utility 'convert'
that belongs to imagemagick. 

Batch processing is generally easier to manage at the
command line, even if it takes you an hour to learn 
how to do it.

cheers and HTH

convert -brightness-contrast <params> input-file output-file

docs from https://imagemagick.org/script/command-line-options.php#brightness-contrast

-brightness-contrast brightness
-brightness-contrast brightness{xcontrast}{%}

Adjust the brightness and/or contrast of the image.

Brightness and Contrast values apply changes to the input image. They are not absolute settings. A brightness or contrast value of zero means no change. The range of values is -100 to +100 on each. Positive values increase the brightness or contrast and negative values decrease the brightness or contrast. To control only contrast, set the brightness=0. To control only brightness, set contrast=0 or just leave it off.

You may also use -channel to control which channels to apply the brightness and/or contrast change. The default is to apply the same transformation to all channels.

Brightness and Contrast arguments are converted to offset and slope of a linear transform and applied using -function polynomial "slope,offset".

The slope varies from 0 at contrast=-100 to almost vertical at contrast=+100. For brightness=0 and contrast=-100, the result are totally midgray. For brightness=0 and contrast=+100, the result will approach but not quite reach a threshold at midgray; that is the linear transformation is a very steep vertical line at mid gray.

Negative slopes, i.e. negating the image, are not possible with this function. All achievable slopes are zero or positive.

The offset varies from -0.5 at brightness=-100 to 0 at brightness=0 to +0.5 at brightness=+100. Thus, when contrast=0 and brightness=100, the result is totally white. Similarly, when contrast=0 and brightness=-100, the result is totally black.

As the range of values for the arguments are -100 to +100, adding the '%' symbol is no different than leaving it off.



> 
> mick
> -- 
> Key ID    4BFEBB31
> 

-- 
Joel Roth