Authors like Graham Greene and JD Salinger were very particular about their book covers.

If you accept the fact that the market is the arbiter of all good taste, the adage 'never judge a book by its cover' no longer holds.  

Graphic design, typography and page layouts have long been considered as 'essentials' for user-friendly books, but book covers got their due only in the mid-1970s, when market forces compelled covers to be both livelier and more intrusive: in other words, to become advertisements.  

'There must be two triggers,' Phil Baines says in Penguin By Design: A Cover Story (1935-2005), 'an initial trigger which will attract the buyer towards the book from the other side of the shop; and then, when he gets to the book, a second trigger which is in some visual and/or literal way intriguing. Then, he actually reaches out and picks the book up.'

With the increasing realisation that book covers were the initial trigger, the visual integrity of Penguin paperbacks was diluted; the insides and outsides of many, if not of most of them, had stopped speaking the same language.  

Integration of this kind is always difficult and rare to achieve but Penguin got around the problem by using plain typography within a specific grid.  

Penguin By Design is the story of how plain typography was replaced by graphics and illustrations that attempted to tell you more about the content than the old-style designs had succeeded in doing.  

Just as truth is never allowed to come in the way of a good story in the popular press, it wasn't faithfulness to the content that inspired designers; their brief was to make covers attractive, or at least unusual so that more copies sold.  

It was the market or the perspectives of publishers who believed there was a nexus between sexual candour/ violence and sales that called the shots. 

Unlike text designs or the insides of books, which mostly follow a small number of set designs, book covers are diverse.

Some books -- for instance, the classics, which are masterpieces of picture research from art galleries around the world, or simple reference books like dictionaries of all kinds -- demanded individual treatment.  

They could not be slotted in a mechanical way within pre-designed formats.

Penguin By Design, divided into five sections that deal with cover designs of different categories of books, begins by showing how Allen Lane, the founder of Penguin, set about producing a branded product.

An original grid was created within which the essential elements or the typeface was 'fitted in'. Identification was an advantage in the lean 1930s and the War years because customers wanted more of exactly the same stuff and didn't have any reasons to try alternatives.

(Readers of Penguin/ Pelican belonged to one class, that is, the top end of the market who were more concerned with content than looks.)

But, by the 1950s, more publishers had pitched into the paperback market and some kind of differentiation became necessary between the staid earlier covers and the others that followed.

The book therefore has two parallel histories: one of changes in the graphic design, the other of changes that were necessitated by making cheap paperbacks, or those meant for down-market mass fiction.

Fiction titles therefore began appearing in different formats, even as heavy publicity was required to promote some of them.

A clear break came with M M Kaye's The Far Pavilions, which showed a couple kissing with the Himalayas in the background, and it went off like a bomb and also spun off into television serials.

The message was loud and clear: Penguin covers were going to change in keeping with what the market wanted.

Yet, the old-style covers continued for some more time. This is because some authors were notoriously sensitive about covers.

J D Salinger, author of bestsellers like The Catcher In The Rye and Fanny And Zooey, wouldn't allow anything but type (he had this written into the contract).

Graham Greene, too, was touchy about what kind of covers were put on his book and eventually settled for a mix of typography and line sketches of his main characters. Certainly, nothing garish was allowed to go through.

But by and large, illustrations became the norm and indeed some covers were far more interesting or attractive than the books they were wrapped around.  

Given the fact that the average buyer doesn't spend more than a few minutes in making up his mind whether to go for the book or not, a visual prod was necessary.  

What makes Penguin By Design a design classic is that it is filled with stunning illustrations with details of individual titles and the designers who created the covers.  

Perhaps, for once the blurb has got it right: 'The inspiring images demonstrate how difficult it is not to judge a book by its cover.'