Line-by-line dataform readers and methods are enabled to operate with reduced buffer memory capacity. Storage and retention of image data are controlled on an interactive basis by concurrent analysis while lines of image data are coupled from a linear scanner. In a first embodiment lines of image data are analyzed for recognition of a feature unique to a type of dataform. Upon successful feature recognition a series of earlier and later lines of image data adequate to include a complete dataform image are retained in memory for decoding purposes. Prior to successful feature recognition, as lines of image data exceeding a limited memory storage capacity are received the earliest stored lines are discarded on a first-in-first-out basis. In a second embodiment, a buffer memory has a storage capacity adequate to store only a partial dataform image. Upon successful dataform feature recognition the type and size of the dataform are determined and decoding of the earliest lines including dataform image data is initiated, before the full dataform image is stored. As decoding progresses, the earliest lines of dataform image data are discarded as later lines of dataform image data are still being coupled from the scanner. Cost and power usage are lowered by reduction of required memory capacity.