I represent a single component of color in JPEG YCbCr color space. I can accept a list of blocks in my component from the current MCU, then stream the samples from this block for use in color conversion. I also store the running DC sample value for my component, used by the Huffman decoder.

The following layout is fixed for the JPEG primitives to work:
currentX <SmallInteger>
currentY <SmallInteger>
hSampleFactor <SmallInteger>
vSampleFactor <SmallInteger>
mcuBlocks <Array of: <IntegerArray of: DCTSize2 * Integer>>
widthInBlocks <SmallInteger>
heightInBlocks <SmallInteger>
dctSize <SmallInteger>
mcuWidth <SmallInteger>
mcuHeight <SmallInteger>
priorDCValue <SmallInteger>

	sample streaming
	initializeSampleStreamBlocks: nextSample resetSampleStream

	accessing	top
	acTableIndex
	acTableIndex:
	dcTableIndex
	dcTableIndex:
	heightInBlocks
	heightInBlocks:
	id
	id:
	mcuWidth:mcuHeight:dctSize:
	priorDCValue:
	qTableIndex
	qTableIndex:
	totalMcuBlocks
	updateDCValue:
	widthInBlocks
	widthInBlocks:

	sample streaming	top
	initializeSampleStreamBlocks:
	nextSample
	resetSampleStream