Image data processing apparatus

An image data processing process for producing image data to be applied to image outputting means which is capable of producing pixels of a plurality of density gradation levels on the basis of inputted image data having values within a range between a lower limit value and an upper limit value, the image data processing process comprising the steps of:

• comparing a minimum value of the inputted image data with a first threshold which is higher than a lower limit input value and lower than an upper limit input image data value;
• comparing a maximum value of the inputted image data with a second threshold which is higher than the first threshold and lower than the upper limit input image data value;
• adopting the minimum value of the inputted image data as a minimum input value if the minimum value of the inputted image data is not higher than the first threshold;
• adopting the lower limit input image data value as the minimum input value if the minimum value of the inputted image data is higher than the first threshold;
• adopting the maximum value of the inputted image data as a maximum input value if the maximum value of the inputted image data is not lower than the second threshold;
• adopting the upper limit input image data value as the maximum input value if the maximum value of the inputted image data is lower than the second threshold;
• and
• correcting the inputted image data so that inputted image data within a range between the minimum input value and the maximum input value thus determined correspond to data within a range between the lower limit value and the upper limit value for input to the image outputting means, to prepare image data to be applied to the image outputting means.

An image outputting apparatus for outputting an image on the basis of inputted image data having values within a range between a lower limit value and an upper limit value, the image outputting apparatus comprising:

• image outputting means capable of producing pixels of a plurality of density gradation levels;
• first comparison means for comparing a minimum value of the inputted image data with a first threshold which is higher than a lower limit input image data value and lower than an upper limit input image data value;
• second comparison means for comparing a maximum value of the inputted image data with a second threshold which is higher than the first threshold and lower than the upper limit input image data value;
• minimum input value determining means for adopting the minimum value of the inputted image data as a minimum input value if the minimum value of the inputted image data is not higher than the first threshold, and adopting the lower limit input image data value as the minimum input value if the minimum value of the inputted image data is higher than the first threshold, on the basis of the comparison by the first comparison means;
• maximum input value determining means for adopting the maximum value of the inputted image data as a maximum input value if the maximum value of the inputted image data is not lower than the second threshold, and adopting the upper limit input image data value as the maximum input value if the maximum value of the inputted image data is lower than the second threshold, on the basis of the comparison by the second comparison means;
• and
• data correction means for correcting the inputted image data so that inputted image data within a range between the minimum input value and the maximum input value thus determined correspond to data within a range between the lower limit value and the upper limit value for input to the image outputting means, to prepare image data to be applied to the image outputting means.