#Xnconvert multipage software
So, what about other digicams / software editors that didn't use the IJG scaling method? People always love to make comparisons, and comparing multiple 64-element matrices is not intuitive to the average person. If we know that a given program has used the IJG scaling method, then we can indeed make a comparison, because all numbers in the matrices will move according to the algorithm in a similar manner. That said, many software programs and some digicams are indeed using scaled versions of this standard table. A quality factor of 100 does not mean Lossless compression! Instead, it generally represents the quality factor that will generate the highest quality compressed image with the provided scaling algorithm. This is NOT a percentage! It is merely a number from 1-100 representing the scaling factor used in generating the table. The IJG group has proposed a method of scaling these coefficients according to a “quality factor” scale. So, then why are “quality” numbers listed for each camera/software source? Many programs encode their JPEG images using quantization tables that are generated by scaling the coefficients in a “standard“ table that is provided in the ITU-T specification. Trying to make a comparison between a pair of matrices is not at all straightforward (or always possible).
JPEG compression quality is actually defined by a pair of quantization tables (each with an array of 64 values). Calvin Hass (Comparing JPEG Quality » Important note about Quality Factors) wrote:It is extremely important that the reader understand that compression quality cannot truly be represented by a single value.
0 kommentar(er)
