What is the difference between "by contrast" and "in contrast?"

Can anyone explain the difference between by contrast and in contrast?

Solution 1:

I don't think there is a difference in meaning, only in usage.
This blog post details it:

“In contrast” and “by contrast” mean the same thing: the act of comparing in order to show differences.
The difference lies in the way the words are used.

• “In contrast” is usually followed by “to” or “with” and requires a noun to follow it.
• “By contrast” is usually followed or preceded by the subject of the sentence.

Examples:

In contrast to the diligent bee, the butterfly flies hither and yon with no apparent purpose.
In contrast with the chorus of birdsongs in my backyard, my front yard is serenaded by the sound of rumbling buses flying down the street.

By contrast, the Picasso is more vibrant and full of life.
The cats will often sleep the day away. The dogs, by contrast, never settle down.

Solution 2:

There is no difference in meaning. But usually:

In contrast + to/with + noun

By Contrast + subject of the sentence

Note: According to Longman Dictionary you can use "in contrast" + "(with/to)"

Example For "in contrast":

The stock lost 60 cents a share, in contrast to last year, when it gained 21 cents.

Examples For "by contrast":

The birth rate for older women has declined, but, by contrast, births to teenage mothers have increased.

Solution 3:

The English make a distinction: in contrast is simply unlike; by contrast is unlike by comparison. Economist March 27th 1993, p. 92.