To achieve a lithographic effect, try one of the following two methods:

Method 1

• Image > Mode > Greyscale
• Filter > Sharpen > Unsharp mask (maximum 500, radius 1 to 2, threshold 0)
• Filter > Artistic > Poster edges (adjust / experiment / play)
• Image > Adjust > Threshold (adjust /experiment /play)

Method 2

• Image > Mode > Greyscale
• Lower contrast to give good detail in both shadows & highlights
• Filter > Sharpen > Unsharp mask (maximum 500, radius 1 to 2, threshold 0)
• Image > Adjust > Threshold (adjust / experiment / play)