In grayscale format even though only gray pixels are present, use.Ĭonvert bird.png -type TrueColor bird.jpg For example, to prevent a JPEG from being written Normally, when a format supports different subformats suchĪs grayscale and truecolor, the encoder will try to choose anĮfficient subformat. Palette, PaletteMatte, TrueColor, TrueColorMatte,ĬolorSeparation, or ColorSeparationMatte. The colourmap is defined by the -type option to IM: -type typeĬhoose from: Bilevel, Grayscale, GrayscaleMatte, Note that a PseudoClass will have a colourmap section but this will be the colour table of the PseudoClass not a Palette type (yes, that is very confusing on IM's side). This is very similar to a PseudoClass since it also is a table of colours, the difference is that a PseudoClass will include only the colours present in the image and the colourmap will include all colours in a pallette. The colourmap is an index of colours against a pallette which is stored in the image. DirectClass and PseudoClass are synonyms to DirectColor and PseudoColor) So, what is a Colourmap? Major operations involving image modifications would generally upgrade PsuedoColor images (images using a color table) to a DirectColor (images using separate color values for every pixel) before the operation is applied. And since IM will almost always convert a PseudoClass image into a DirectClass image I was baffled. This was the source of my confusion: a PseudoClass is not a colourmap, they are different things. A PseudoClass uses a colour table and then stores offsets into that table.A DirectClass stores the colour values for every pixel.First of all there is a difference between DirectClass and PseudoClass: Reading the IM forums I finally (more-or-less) understood what is a colourmap in an image and how to deal with it. TL DR: Use -type TrueColor to remove colourmaps, either from Palette types of PseudoClass images. Thanks to for pointing me in the right direction. How can I force IM to perform a more consistent behaviour (preferably not adding colourmaps to anything)?Ĭan I forcefully remove a colourmap? (I'm trying for 5 hours without success.) How IM performs the decisions of (1) changing the colourspace of the image during the convert and (2) the decision of adding a colourmap? Nevertheless, this raises three questions: The colourmap now breaks some of my thumbnail making scripts (the majority of images I use are actually much bigger but these two are the ones I experimented on the most on it is a web game). But one of the images now is in grayscale and another is in sRGB, moreover, IM added a colourmap to one fo the images: identify -verbose image1.jpg | grep -A 2 Colorġ520: (217,217,217) #D9D9D9 identify -verbose image2.jpg | grep -A 2 Color Image2.png PNG 69x102 69x102+0+0 8-bit sRGB 2040B 0.000u identify -verbose image1.png | grep -A 2 Colorġ357: (217,217,217,255) #D9D9D9FF identify -verbose image2.png | grep -A 2 Colorġ: ( 26, 26, 26,255) #1A1A1AFF graya(26,1)īoth have less than 255 colours (needed for a greyscale) so let's try to convert them to JPEGs: convert image1.png -strip -quality 80 convert image2.png -strip -quality 80 image2.jpg Let's have a look at what IM thinks of their colourspaces: identify * I've updated to IM 6.9.9-3 recently and found some very inconsistent behaviour.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |