CODEWITHSUNDEEP
phpcssimagegraphicsimagemagick
Epsiloncool
Epsiloncool

Reputation: 1473

CSS brightness/contrast at the server side

Looking for answer for 2 weeks. I have a tool which allows to adjust images' contrast and brightness directly in the web browser and use CSS3 properties to show result. But I should also apply these modification to original JPG at the server-side and output it back to user.

How can I do it? I am using PHP+Imagemagick, but can not find a way to do this conversion. Please help me.

Upvotes: 1

Views: 1101

Answers (3)

user2949702
user2949702

Reputation:

The CSS3 brightness filter simply multiplies the color values by the given constant.[1][2] To achieve the same effect with Imagemagick, use -evaluate Multiply[3]. Alternatively, -function Polynomial[4] can be used for the same effect. Other features such as -level[5][6] and -brightness-contrast[7][8] are less appropriate, because they multiply the color by the inverse of the given constant.

The CSS property filter: brightness(80%) corresponds to the Imagemagick option -evaluate Multiply .8.

The CSS property filter: brightness(120%) corresponds to the Imagemagick option -evaluate Multiply 1.2.

Setting options for Imagemagick in PHP (or migrating from PHP to something better) is an exercise for the reader.

Upvotes: 1

Epsiloncool
Epsiloncool

Reputation: 1473

I found a great function of ImageMagick which allows us to do anything with brightness and contrast. It is "-level".

But it doesn't allow to apply CSS3 brightness and contrast values directly. Thus I made a great investigation and calculate special formula to transfer CSS brightness and contrast values to "black point" and "white point" parameters of "-level" option. Please check this page (sorry, russian language, but you can use google translate). Roll to the bottom of page if you don't want to read all these equations.

Upvotes: 1

BaBL86
BaBL86

Reputation: 2622

You need to transfer your client brightness settings and then apply them to original JPG with

bool Imagick::modulateImage ( float $brightness , float $saturation , float $hue )

function. More this

Upvotes: -1

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